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OpenVMS Glossary
Order Number: AA-PV5UA-TK
May 1993
This document contains definitions for commonly used terms in
documentation of the OpenVMS operating system.

Revision/Update Information:

This manual supersedes the VMS
Glossary, Version 5.5.

Software Version:

OpenVMS AXP Version 1.5
OpenVMS VAX Version 6.0

Digital Equipment Corporation
Maynard, Massachusetts

May 1993
Digital Equipment Corporation makes no representations that the use of its products in the
manner described in this publication will not infringe on existing or future patent rights, nor do
the descriptions contained in this publication imply the granting of licenses to make, use, or sell
equipment or software in accordance with the description.
Possession, use, or copying of the software described in this publication is authorized only pursuant
to a valid written license from Digital or an authorized sublicensor.
© Digital Equipment Corporation 1993. All rights reserved.
The postpaid Reader’s Comments forms at the end of this document request your critical evaluation
to assist in preparing future documentation.
The following are trademarks of Digital Equipment Corporation: Alpha AXP, AXP, CI, CMI,
DECdtm, DECmigrate, DECnet, DECwindows, DECwriter, Digital, DNA, Ethernet, HSC, IAS,
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DOCUMENT, VAX FORTRAN, VAXft, VAX MACRO, VMS, VMScluster, VT100, the AXP logo, and
the DIGITAL logo.
ZK4507

This document was prepared using VAX DOCUMENT Version 2.1.

Preface
Intended Audience
This document is intended for all users of OpenVMS documentation.

Document Structure
The terms are presented in alphabetical order. They have not been grouped into
categories.

Conventions
In this manual, every use of OpenVMS AXP means the OpenVMS AXP operating
system, every use of OpenVMS VAX means the OpenVMS VAX operating system,
and every use of OpenVMS means both the OpenVMS AXP operating system and
the OpenVMS VAX operating system.
Note
In this document, discussions that refer to VMScluster environments
apply to both VAXcluster systems that include only VAX nodes and
VMScluster systems that include at least one AXP node unless indicated
otherwise.

iii

Glossary
$allocation-class$
Part of a naming convention for physical devices. This convention is described in
the OpenVMS Cluster Systems manual.
‘‘a’’ character
The subset of ASCII characters that are allowed in the labels of ANSI-labeled
magnetic tape.
abort
An exception occurring in the middle of an instruction that sometimes leaves the
registers and memory in an indeterminate state such that the instruction cannot
necessarily be restarted.
absolute time
A value expressing a specific date (month, day, and year) and time of day.
Absolute time values are always expressed in the system as positive numbers.
access control
(1) Restrictions on the ability of a subject (user or process) to use the system
or an object in the computing system. Authentication of the user name and
password controls access to the system, while protection codes and access control
lists regulate access to protected objects in that system.
(2) In DECnet for OpenVMS, the process of screening inbound connect requests
and verifying them against a local system account file.
access control entry (ACE)
An entry in an access control list. ACEs may specify identifiers and the access
rights to be granted or denied the holders of the identifiers, default protection for
directories, or security alarm details. ACLs for each object can hold numerous
entries, limited only by overall space and performance considerations.
access control list (ACL)
A list that defines the kinds of access to be granted or denied to users of an
object. Access control lists can be created for objects such as files, devices, and
mailboxes. Each ACL consists of one or more entries known as access control list
entries.
access control string
A series of 0 to 42 characters that contains login information to be sent to a
remote node. An access control string usually consists of a username, spaces or
tabs, and a password.

Glossary–1

access mode
A processing mode that determines which instructions a processor can execute
and which locations in memory it can read and write. The four processor access
modes (in order from most to least privileged and protected) are: kernel (mode
0), executive (mode 1), supervisor (mode 2), and user (mode 3). When the
processor is in kernel mode, the executing software has complete control of,
and responsibility for, the system. The processor status longword contains the
current access mode field. The operating system uses access modes to define
protection levels for software executing in the context of a process. For example,
the executive service and most system services run in kernel mode and are most
protected. OpenVMS Record Management Services (RMS) and some system
services run in executive mode. The command interpreter is less protected
and runs in supervisor mode. The debugger runs in user mode with the same
privileges and protection as normal user programs. See record access mode.
access type
(1) The way a procedure accesses its arguments. See record access type
(2) The right to perform an operation on a protected object. A security policy
can require multiple access rights to complete an operation. A file, the most
commonly accessed object, can require read, write, execute, delete, or control
access.
access violation
An exception that takes place on an attempt to reference an address that is either
not mapped into virtual memory or not accessible by the current access mode.
account
Every user must have an account to use the system. The account is identified by
the user’s username. Different accounts allow different levels of service from the
system (for example, the privileges users hold, the times during which they can
log in, and so on).
accounting file
A file that contains information about system resource use. The information is
stored in binary format: you cannot print it with the PRINT command or type
it with the TYPE command. To process the accounting file, use the Accounting
utility. See current accounting file.
account name
The string in the account field of the user authorization file (UAF) that shows the
name of the user’s accounting group.
ACE
See access control list entry.
ACL
See access control list.
ACP
See ancillary control process.

Glossary–2

active component
A network component whose operational state is other than OFF. The ACTIVE
keyword can be used with the Network Control Program (NCP) commands SHOW
or LIST to display information about active lines, circuits, nodes, and logging.
active member
A shadow set member that is fully consistent with all other active members of
the shadow set.
active set
In a symmetric multiprocessing system, those processors that have been
bootstrapped into the system, have undergone initialization, and are capable
of scheduling and executing processes. Together, the primary processor and all
secondary processors make up a system’s active set. See available set.
adapter control block (ADP)
A structure in the I/O database that describes an adapter or device controller and
the I/O interconnect to which it is attached.
address
A number used by the operating system and user software to identify a storage
location in memory. See virtual address and physical address.
address access type
A type of access in which the specified operand of an instruction is not accessed
directly by the instruction. The address of the specified operand is the actual
instruction operand, and the context of the address calculation is determined by
the data type of the operand.
address space
The set of all possible addresses available to a process. Virtual address space
refers to the set of all possible virtual addresses. Physical address space refers to
the set of all possible physical addresses transmitted on the processor-to-memory
interconnect.
adjacent node
A network node connected to the local node by a single physical line.
ADP
See adapter control block.
affinity
In a symmetric multiprocessing system, a close association of a device or a
process with a specific processor or set of processors in the system. See device
affinity and process affinity.
alarm
See security alarm.
alert
A mechanism by which a thread informs either itself or another thread to
terminate as soon as possible. Alert and cancel have the same meaning.

Glossary–3

alertable
A routine in which synchronous alert delivery can occur only at specific,
well-defined points. These points are DECthreads routines that determine if an
alert is pending and, if so, deliver the alert.
alertsafe
A routine that can be called without risk of triggering an alert while
asynchronous delivery of alerts is enabled.
alignment
Placement of a data item at an address in memory that is an even multiple of
some machine-dependent unit, such as a longword or quadword. See natural
alignment.
allocating
Reserving a particular device unit for exclusive use. A user process can allocate a
device only when that device is not allocated by any other process.
allocation class
A unique number between 0 and 255 that the system manager assigns to a pair
of hosts and to the dual-pathed devices that the hosts make available to other
nodes in the VMScluster configuration. (Allocation class 0 is used to denote that
the node is not a member of any allocation class.) The allocation class provides
a way for users to access dual-pathed devices through either of the hosts. In
this way, if one host of an allocation class set is not available, the user can gain
access to a device specified by that allocation class through the other host of the
allocation class.
Alpha Primary Bootstrap (APB)
The primary bootstrap program that initializes an AXP system with OpenVMS
AXP. The program is located in the boot block of physical memory and is the first
program read by the CPU when a processor is booted after it has been halted.
alphanumeric character
An uppercase or lowercase letter, a dollar sign, an underscore, or a decimal digit.
alphanumeric UIC
A format of user identification code (UIC) that specifies the user’s group (optional)
and member in alphanumeric form rather than numeric form.
alternate key
An optional key within the data records in an indexed file; used by OpenVMS
Record Management Services (RMS) to build an alternate index. See key indexed
files and primary key.
American Standard Code for Information Interchange (ASCII)
A set of 8-bit binary numbers representing the alphabet, punctuation, numerals,
and other special symbols used in text representation and communications
protocol.

Glossary–4

ancillary control process (ACP)
A process that acts as an interface between user software and an I/O driver. An
ACP provides functions supplemental to those performed in the driver, such as
file and directory management. Two examples of ACPs are the magnetic tape
ACP and the network ACP.
AP
See argument pointer.
APB
See Alpha Primary Bootstrap.
application
A set of tasks related by the business activity they support and controlled as a
single unit. See transaction processing.
area
(1) A region of an indexed file maintained by OpenVMS Record Management
Services (RMS) that allows a user to specify placement or specific bucket sizes or
both for particular portions of a file. An area consists of any number of buckets;
there may be from 1 to 255 areas in a file.
(2) A group of nodes in a network that can run independently as a subnetwork.
area router
See level 2 router.
area routing
A technique for grouping the nodes in a network into areas for routing purposes.
Routing in a multiple-area network is on two levels, with one level of routing
within an area (called level 1 routing) and a second, higher level of routing
between areas (called level 2 routing). Area routing permits a DECnet for
OpenVMS network to support the configuration of very large networks.
argument information register
On AXP systems, integer register 25 (R25). In a standard call this register
describes the argument list.
argument list
A vector of entries (longwords on VAX systems and quadwords on AXP systems)
that represent a procedure parameter list and possibly a function value.
argument pointer (AP)
General register 12 on VAX systems. By convention, AP contains the address of
the base of the argument list for procedures initiated using CALL instructions.
ASCII
See American Standard Code for Information Interchange.
ASMP
See asymmetric multiprocessing.

Glossary–5

assembler
A language processor that translates a source program containing assembly
language directives and machine instructions into an object module.
assembly language
A machine-oriented programming language. VAX MACRO is the assembly
language for the VAX computer. MACRO–64 for OpenVMS AXP systems is the
assembly language for the Alpha AXP computer. See binary machine code.
assigning a channel
Establishing the necessary software link between a user process and a device
unit that allows a user process to communicate with the device.
assignment statement
In DIGITAL Command Language (DCL), the association of a symbol name to
use with a character string or numeric value. Symbols can define synonyms for
system commands or can be used for variables in command procedures.
AST
See asynchronous system trap.
ASTLVL
See asynchronous system trap level.
ASTSR
See asynchronous system trap summary register.
asymmetric multiprocessing (ASMP)
A multiprocessing configuration in which the processors are not equal in their
ability to execute operating system code. In general, a single processor is
designated as the primary, or master, processor; other processors are the slaves.
The slave processors are limited to performing certain tasks, whereas the master
processor can perform all system tasks. See symmetric multiprocessing.
asynchronous record operation
A mode of record processing in which a user program can continue to execute
after issuing a record retrieval or storage request without having to wait for the
request to be fulfilled.
asynchronous software interrupt
An asynchronous interruption of normal code flow caused by some software event.
This interruption shares many of the properties of hardware exceptions that
include forcing some out-of-line code to execute.
asynchronous system trap (AST)
A software-simulated interrupt to a user-defined service routine. ASTs enable a
user process to be notified asynchronously, with respect to that process, of the
occurrence of a specific event. If a user process has defined an AST routine for an
event, the system interrupts the process and executes the AST routine when that
event occurs. When the AST routine exits, the system resumes execution of the
process at the point where it was interrupted.

Glossary–6

asynchronous system trap level (ASTLVL)
On VAX systems, a value kept in an internal processor register that is the most
privileged access mode for which an AST is pending. The AST does not occur
until the current access mode drops in privilege (rises in numeric value) to a
value greater than or equal to ASTLVL. Thus, an AST for an access mode is not
serviced while the processor is executing in a more privileged access mode.
asynchronous system trap summary register (ASTSR)
On AXP systems, the register that contains a bitmask of the access modes for
which an asynchronous system trap, or AST, is pending. An AST for a given
access mode represented by a bit set in this register does not occur while the
current access mode is more privileged than the access mode of the AST.
atomic instruction
An instruction that consists of one or more discrete operations that are handled
by the hardware as a single operation, without interruption.
atomicity
A requirement that either all operations of a transaction are made permanent or
none of them are made permanent.
atomic operation
An operation that cannot be interrupted by other system events, such as an
asynchronous system trap (AST) service routine. An atomic operation appears
to other processes to be a single operation. Once an atomic operation starts, it
always completes without interruption.
Read-modify-write operations are typically not atomic at an instruction level on a
RISC machine.
attached processor
See secondary processor.
attribute
(1) In the security context, a characteristic of an identifier or the holder of an
identifier. Attributes can enhance or limit the rights granted with an identifier.
For example, a user holding an identifier with the resource attribute can charge
disk space to the identifier.
(2) In threads, the individual components of the attributes object. Attributes
specify detailed properties about the objects to be created.
attributes object
An object that holds the individual attribute values to be used when creating
threads, mutexes, or condition variables. An attributes object is analogous to a
type definition in a programming language. It describes details of the objects to
be created.
audit
See security audit.

Glossary–7

auditing
To record the occurrence of events with security implications as they occur on the
system and, later, to examine system activity for possible security violations or
improper use of the system. Security-relevant events include activities such as
logins, breakins, changes to the authorization database, and access to protected
objects. Event messages can be sent as alarms to an operator terminal or written
as audit records to a log file.
authentication
The act of establishing the identity of users when they start to use the system.
OpenVMS (and most other commercial operating systems) uses passwords as the
primary authentication mechanism.
authorization file
See user authorization file.
automatic record locking
A OpenVMS Record Management Services (RMS) capability that allows a user to
lock only one record in a specific shared file at any given time. The lock occurs
on every execution of a $FIND or $GET macroinstruction (unless the NLK bit
is set in the record processing field). The lock is released when the next record
is accessed, when the current record is updated or deleted, when the record
stream is disconnected, or when the file is closed. OpenVMS Record Management
Services (RMS) maintains locks on modified records during a recovery unit.
availability
The percentage or amount of scheduled time that a computing system provides
application service.
available set
In a symmetric multiprocessing system, those processors that have passed the
system’s power-on hardware diagnostics and may or may not be actively involved
in the system. The available set includes the active set. See active set.
backplane interconnect
On VAX systems, an internal processor bus that allows I/O device controllers to
communicate with main memory and the central processor. These I/O controllers
may reside on the same bus as memory and the central processor (for instance,
in VAX 8200, VAX 8250, VAX 8300, VAX 8350 systems), or they may be on a
separate bus entirely (for instance, in a VAX–11/780 or VAX 8600/8650 system).
In the latter case, an I/O adapter enables and controls the communications
between the I/O bus and the processor and memory.
The backplane interconnect is called the synchronous backplane interconnect, or
SBI, in the VAX–11/780 and VAX 8600 family of systems; the CPU-to-memory
interconnect, or CMI, on the VAX–11/750 processor; and the VAXBI in the VAX
8500 family of systems, the VAX 8700, the VAX 8800, the VAX 8200 family of
systems, the VAX 8300 family of systems, the VAX 6200 family of systems, and
the VAX 6300 family of systems. The MicroVAX 3000 series and MicroVAX II
processors use the Q22–bus as a backplane. See processor-memory interconnect.

Glossary–8

backup switching
When a second computing system or component picks up processing in the event
that the primary computing system or component fails.
balance set
The collection of all process working sets currently resident in physical memory.
The balance set is maintained by the system’s swapper process.
bandwidth
The range of frequencies assigned to a channel or system; that is, the difference
expressed in Hertz between the highest and lowest frequencies of a band.
base priority
The priority that the system assigns to a process when it is created. A base
priority generally comes from the authorization file. The scheduler never
schedules a process below its base priority. The base priority can be modified
only by the system manager or the process itself. The base priority of a running
process can be altered by any user with ALTPRI privilege.
batch job
A program that is scheduled and executed under the control of the batch
processing subsystem. Control input for a batch job comes from a command
procedure stored on disk, and output is directed to a disk file.
batch processing
A mode of processing in which all commands to be executed by the operating
system (and, optionally, data to be used as input to the commands) are placed in
a file or punched onto cards and submitted to the system for execution as a single
unit. See command procedure.
baud rate
The speed at which a terminal transmits or receives characters.
BCUG
See bilateral closed user group.
bilateral closed user group (BCUG)
An optional packet switching data network facility that restricts pairs of data
terminal equipment (DTE) on communicating with each other.
binary machine code
The internal instruction format used by the computer. It is called binary
because only two characters—0 and 1—are used in this code. Programmers use
languages, compilers, and the assembler to generate the binary code.
binding
See linking.
bits per inch (bpi or bits/in)
The recording density of a magnetic tape; indicating how much data can fit on 1
inch of the recording surface. See density.

Glossary–9

bit string
See variable-length bit field.
block
(1) The smallest logically addressable unit of data that a specified device can
transfer in an I/O operation (512 contiguous bytes for most disk devices).
(2) An arbitrary number of contiguous bytes used to store logically related status,
control, or other processing information.
(3) To prevent a thread from executing.
blocking AST
An AST that can be requested by a process using the lock management system
services. A blocking AST is delivered to the requesting process when it is
preventing another process from accessing a resource.
block I/O
A data-accessing technique in which the program manipulates the blocks
(physical records) that make up a file, instead of its logical records; allows for
the direct access to the blocks in a file without regard for the file organization or
record format.
boot
Short for bootstrap. A bootstrap is a technique or device by which the system
brings itself into a desired state by means of its own action, such as a routine
whose first few instructions are sufficient to bring the rest of the routine into
memory from an input device. Bringing a fresh operating system into memory is
called booting.
boot name
The abbreviated name of the device being used to boot software. For example,
DU0 is the boot name for device DU0.
boot server
The management center for a VMScluster system and its major source provider.
The boot server provides disk access and downline loads satellite nodes.
bootstrap block
A block in the index file of a system disk. It can contain a program that loads the
operating system into memory.
bound procedure
A type of procedure that requires knowledge (at run-time) of a dynamically
determined larger enclosing scope to function correctly.
bpi or bpi/in
See bits per inch.
breach
A break in the system security that results in admitting a person or program to
an object.

Glossary–10

break-in attempt
An effort made by an unauthorized source to gain access to the system. Since the
first system access is achieved through logging in, break-in attempts primarily
refer to attempts to log in illegally. These attempts focus on supplying passwords
for users known to have accounts on the system through informed guesses or
other trial-and-error methods.
broadcast
In threads, a mechanism to wake all threads waiting on a condition variable. See
signal.
broadcast addressing
In an Ethernet network, a special type of multicast addressing in which all nodes
are to receive a message.
broadcast circuit
A circuit having multiple nodes connected to it and having a method for
transmitting a message that will be received by multiple receivers.
bucket
A storage structure of 1 to 32 blocks used for building and processing files of
relative and indexed organization. A bucket contains one or more records or
record cells. Buckets are the unit of contiguous transfer between OpenVMS
Record Management Services (RMS) buffers and the disk.
bucket locking
A facility that prevents access to any record in a bucket by more than one user
until that user releases the bucket.
bucket split
The result of inserting records into a full bucket. To minimize bucket splits,
OpenVMS Record Management Services (RMS) attempts to keep half of the
records in the original bucket and transfers the remaining records to a newly
created bucket.
buffer
An internal memory area used for temporary storage of data records during input
or output operations.
buffered data path
A UNIBUS adapter data path that transfers 32 or 64 bits of data in a single
synchronous backplane interconnect, or SBI, transfer.
buffered I/O
An I/O operation, such as terminal or mailbox I/O, in which an intermediate
buffer from the system buffer pool is used instead of a process-specified buffer.
See direct I/O.
bugcheck
An internal inconsistency that the operating system cannot resolve. If a nonfatal
bugcheck is declared, an error log entry is made. If the system cannot continue to
run, a fatal bugcheck is declared and the system produces a crash dump.

Glossary–11

busywait
See spin wait.
byte
Eight contiguous bits starting on any addressable boundary. Bits are numbered 0
to 7 from right to left. Bit 0 is the low-order bit. When interpreted arithmetically,
a byte is a two’s complement integer with significance increasing from bits 0
through 6. Bit 7 is the sign bit. The value of the signed integer is in the range
–128 to +127 decimal. When interpreted as an unsigned integer, significance
increases from bits 0 through 7 and the value of the unsigned integer is in the
range 0 to 255 decimal. A byte can be used to store one ASCII character.
byte granularity
A property of memory systems in which adjacent bytes can be written
concurrently and independently by different processes or processors.
cache memory
A small, high-speed memory placed between slower main memory and the
processor. A cache increases effective memory transfer rates and processor speed.
It contains copies of data recently used by the processor and fetches several
bytes of data from memory in anticipation that the processor will access the next
sequential series of bytes.
call
To transfer control to a specified routine.
call frame
The body of information that a procedure must save to allow it to properly return
to its caller. A call frame may exist on the stack or in registers. A call frame may
optionally contain additional information required by the called procedure. See
stack frame.
call instructions
The VAX processor instructions CALLG (call procedure with general argument
list) and CALLS (call procedure with stack argument list).
call stack
The stack and the conventional stack structure used during a procedure call.
Each access mode of each process context (user, supervisor, executive, and kernel)
has one call stack and, on VAX systems, the interrupt service context has one call
stack.
cancel
A mechanism by which a thread informs either itself or another thread to
terminate as soon as possible. Cancel and alert have the same meaning.
capability
In a symmetric multiprocessing environment, an attribute of a single processor
or set of processors. The capabilities required by a given process determine
the set of processors on which it can be scheduled. For instance, the routine
that maintains the system time can execute only on the processor that has the
timekeeper capability.

Glossary–12

captive account
A type of account that limits the activities of the user. Typically, the user is
restricted to using certain command procedures and commands. For example,
the user may not be allowed to use the Ctrl/Y key. This type of account is
synonymous with a turnkey or tied account.
carrier sense
A signal provided by the Physical layer of the DECnet for OpenVMS architecture
to indicate that one or more stations (nodes) are currently transmitting on the
Ethernet channel.
Carrier Sense, Multiple Access with Collision Detect (CSMA/CD)
A link management procedure used by the Ethernet. Allows multiple stations
to access the broadcast channel at will, avoids contention by means of carrier
sense and deference, and resolves contention by means of collision detection and
retransmission.
CCB
See channel control block.
CCITT
Comité Consultatif International Télégraphique et Téléphonique (International
Telegraph and Telephone Consultative Committee). An international consultative
committee that sets international communications usage standards.
central processing unit (CPU)
The hardware that handles all calculating and routing of input and output as
well as executing programs. In short, the CPU is the part of the computer that
actually computes.
channel
(1) A logical path connecting a user process to a physical device unit. A user
process requests the operating system to assign a channel to a device so the
process can communicate with that device. See controller data channel.
(2) A means of transmission over a packet switching data network. For the
VAX Packetnet System Interface (PSI), a logical path between data terminal
equipment (DTE) and data circuit-terminating equipment (DCE) over which data
is transmitted. Each channel is identified by a unique reference number called a
logical channel number (LCN).
channel control block (CCB)
A structure in the I/O database created by the Assign I/O Channel system service
to describe the device unit to which a channel is assigned.
channel request block (CRB)
A structure in the I/O database that describes the activity on a particular
controller. The channel request block for a controller contains pointers to the
wait queue of drivers ready to access a device through the controller.
character
A symbol represented by an ASCII code. See alphanumeric character.

Glossary–13

character buffer
A temporary storage area used to store the last character deleted by an EDT
delete character operation.
characteristics
A display type for the Network Control Program (NCP) commands SHOW and
LIST. It refers to static information about a component that is kept in either
the volatile or permanent database. Such information may include parameters
defined for that component by either the SET or DEFINE command.
character string
A contiguous set of bytes. A character string is identified by two attributes: an
address and a length. Its address is the address of the byte containing the first
character of the string. Subsequent characters are stored in bytes of increasing
addresses. The length is the number of characters in the string.
character string descriptor
A quadword data structure used for passing character data (strings). The first
word of the quadword contains the length of the character string. The second
word can contain type information. The remaining longword contains the address
of the string.
CI
See computer interconnect.
CI only VMScluster configuration
A type of VMScluster configuration in which the computer interconnect, or CI,
device is used for most interprocessor communication. In these configurations, a
node may be a VAX processor or a hierarchical storage controller, or HSC.
circuit
Virtual communication paths between nodes or data terminal equipment (DTE).
Circuits operate over physical lines and are the media on which all I/O occurs.
X.25 circuits are virtual circuits.
CISC
See Complex Instruction Set Computer.
client
A computing system entity that uses the services of other system entities called
servers.
client/server
A style of computing in which a server system provides common database access,
performs computations, and assumes system management tasks for its clients.
close
To terminate all operations on a file.

Glossary–14

closed user group (CUG)
An optional packet switching data network facility that restricts two or more
DTEs in the same group to communicating with each other. The basic CUG also
prevents these DTEs from accessing or being accessed by other DTEs outside the
group. Additions to the basic CUG facility allow one or more DTEs to access or
be accessed by DTEs outside the group.
cluster
(1) A set of contiguous blocks that is the basic unit of space allocation on a
Files–11 disk volume.
(2) A set of pages brought into memory in one paging operation (page fault
cluster).
(3) An event flag cluster.
CMI
See computer memory interconnect.
CMP
See compatibility mode bit.
collating sequence
An order assigned to the characters of a character set (for example, ASCII,
multinational, or EBCDIC) used for sequencing purposes.
collision
Multiple network transmissions overlapping in the physical channel, resulting in
garbled data and necessitating retransmission.
collision detect
A signal provided by the Physical layer of the DECnet for OpenVMS architecture
to its Data Link layer to indicate that one or more stations (nodes) are contending
with the local station’s transmission.
command
In DIGITAL Command Language (DCL), an instruction, generally an English
word, entered by the user at a terminal or included in a command procedure. A
command requests the software monitoring a terminal or reading a command
procedure to perform some well-defined activity. For example, entering the COPY
command requests the system to copy the contents of one file into another file.
command file
See command procedure.
command image
A program associated with and invoked by a DCL command.
command interpreter
A procedure-based system code that executes in supervisor mode in the context of
a process to receive, to check the syntax of, and to parse commands entered by
the user at a terminal or submitted in a command file.

Glossary–15

command language interpreter
See command interpreter.
command level
Input stream for the command interpreter. The initial input stream is always
command level 0. An interactive command procedure begins executing at
command level 1. A batch job command procedure begins executing at command
level 0. You can use the execute procedure (@) command or the CALL command
in a command procedure to create up to 32 nested command levels.
command node
The node from which a Network Control Program (NCP) command is issued.
command parameter
The positional operand of a command delimited by spaces, such as a file
specification, option, or constant.
command procedure
A file containing commands and data that the command interpreter can accept
in lieu of the user’s entering the commands individually on a terminal. Thus,
command procedures provide a means of automatically passing commands to the
operating system. In addition, they permit users to employ such programming
techniques as loops, counters, labels, and symbol substitution to set up elaborate
command sequences that can be altered through user interaction. Command
procedures can also be submitted to the system for processing as batch jobs.
command string
A line (or set of continued lines) containing a command and, optionally,
information modifying the command. A complete command string consists of
a command, its qualifiers, if any, and its parameters (file specifications, for
example), if any, and their qualifiers, if any. A command string is normally
terminated by pressing the Return key.
common
A VAX FORTRAN term for a program section that contains only data.
common event flag cluster
A set of 32 event flags that enables cooperating processes to post event
notification to each other. Common event flag clusters are created as they are
needed. A process can associate with up to two common event flag clusters.
compatibility
The ability of programs written for one type of computer system (such as VAX) to
execute on another type of system (such as AXP).
compatibility mode
A mode of execution that enables the central processor to execute nonprivileged
PDP–11 instructions. The operating system supports compatibility mode
execution by providing an RSX–11M execution environment for an RSX–11M
task image. The operating system compatibility mode procedures intercept
calls to the RSX–11M executive and convert them to the appropriate operating
system functions. Note that a layered product, VAX–11 RSX, is required for the
RSX–11M environment.
Glossary–16

compatibility mode bit (CMP)
The compatibility mode bit in the VAX processor status longword.
compiler
A system component that translates a program written in a high-level language
into an object module in binary machine code.
complete crash dump
A crash dump that contains the complete contents of all of physical memory.
Complex Instruction Set Computer (CISC)
A computer that has individual instructions that perform complex operations,
including complex operations performed directly on locations in memory.
Examples of such operations include instructions that do multibyte data moves
or substring searches. CISC computers are typically contrasted with Reduced
Instruction Set Computer (RISC) computers.
component
An element in a network that can be controlled and monitored. Components
include lines, circuits, nodes, modules, logging, and objects. Components form
part of the Network Control Program (NCP) command syntax.
computer interconnect, CI
A high-speed, fault-tolerant, dual-path bus, which has a bandwidth of 70
megabits per second. With the CI, any combination of processor nodes and
intelligent I/O subsystem nodes — up to 16 in number — can be loosely coupled
in a computer-room environment.
computer memory interconnect, CMI
The part of the VAX–11/750 hardware that connects the processor, memory
controllers, MASSBUS adapters, and the UNIBUS interconnect.
computing component
Part of the total computing system around which an arbitrary boundary has been
defined. The boundary can be defined at any level.
concatenate
To link together in a series.
concealed device
An I/O device that has a logical name associated with it; users thus see the
logical name, rather than the device name, displayed in most system responses.
concurrency
Simultaneous operations by multiple agents on a shared object.
condition
An error state that exists when an exception occurs. See exception and condition
handler.

Glossary–17

condition codes
The 4 bits in the VAX processor status word that indicate the results of previously
executed instructions.
condition handler
A procedure that the system executes when a process exception occurs. When
an exception occurs, the operating system searches for a condition handler and,
if found, initiates the handler immediately. The condition handler may perform
some action to change the situation that caused the exception and continue
execution for the process that incurred the exception. Condition handlers execute
in the context of the process at the access mode of the code that incurred the
exception.
condition value
A 32-bit value (sign-extended to a 64-bit value on AXP systems) used to uniquely
identify an exception condition. A condition value can be returned to a calling
program as a function value or signaled using the signaling mechanism.
condition variable
A synchronization object used in conjunction with a mutex. A condition variable
allows a thread to be blocked until some event happens.
configuration database
A database containing files that provide information about network components.
Specifically, the files contain information about the local node, and all nodes,
modules, circuits, lines, logging, and objects in the network. See permanent
database and volatile database.
configuration register
A control and status register (CSR) for an adapter; for example, a UNIBUS
adapter. It resides in the adapter’s I/O space.
congestion loss
A condition in which data packets transmitted over a network are lost when the
DECnet for OpenVMS Routing layer is unable to buffer them.
connection
The logical path in system communications architecture by which two processes
communicate.
connector node
A node that serves as an X.25 gateway to permit host nodes to access a packet
switching data network.
connect-to-interrupt
A function by which a process connects to a device interrupt vector. To perform a
connect-to-interrupt, the process must map to the program I/O space containing
the vector. See page frame number mapping.
consistent
A shadow set is consistent when every logical block on a member unit contains
exactly the same data as the same logical block on the other members.

Glossary–18

console
The manual control unit integrated into the central processor. The console
enables the operator to start and stop the system, monitor system operation, and
run diagnostics.
console terminal
The video or hardcopy terminal connected to the central processor console.
context
See process context.
context indexing
The ability to index through a data structure automatically because the size of
the data type is known and used to determine the offset factor.
context switching
On VAX systems, interrupting the activity in progress and switching to another
activity. Context switching occurs as one process after another is scheduled for
execution. The operating system saves the hardware context of the interrupted
process in its hardware process control block (PCB) using the Save Process
Context instruction, and loads the hardware PCB of another process into the
hardware context using the Load Process Context instruction, thus scheduling
that process for execution.
On AXP systems, the operating system saves the hardware context of the
interrupted process in its hardware privileged context block (HWPCB) using the
swap privileged context instruction, and loads the HWPCB in the same operation.
contiguous area
A group of physically adjacent blocks on a device or in memory.
continuation character
A hyphen placed at the end of a command line, which allows the user to continue
the command string on the next line after the Return key is pressed.
control and status register (CSR)
A device or controller register residing in the processor’s I/O space. The CSR
initiates device activity and records its status.
control key
The keyboard character that causes a control action. A control key is usually the
combination of the Ctrl key and an alphabetic key, for example, Ctrl/Y.
controller
The part of a mass storage subsystem responsible for interfacing between drives
and computers. Controllers usually multiplex the services of one or more drives
among the demands of one or more host computers.
controller data channel
A logical path to which a driver for a device on a multidevice controller must be
granted access before it can activate a device.

Glossary–19

control region
The highest-addressed half of per-process space (the P1 region). Control region
virtual addresses refer to the process-related information used by the system
to control the process, such as the kernel, executive, and supervisor stacks;
the permanent I/O channels; exception vectors; and dynamically used system
procedures (such as the command interpreter). The user stack is also normally
found in the control region.
control region base register (P1BR)
On VAX systems, the processor register, or its equivalent in a hardware process
control block, that contains the base virtual address of a process control region
page table.
control region length register (P1LR)
On VAX systems, the processor register, or its equivalent in a hardware process
control block, that contains the number of nonexistent page table entries for
virtual pages in a process control region.
control region page table (P1PT)
The page table that maps the control region of virtual address space.
control station
The network node at the controlling end of a multipoint circuit. The control
station controls the tributaries for that circuit.
cooperating tasks
Two tasks that communicate with each other in a task-to-task communication
environment. In particular, cooperating tasks must agree on optional user data
to be passed, how they will send and receive messages to ensure that there is one
transmit for each receive, and which task will disconnect the link.
copy-on-reference
A method used in memory management for sharing data until a process
accesses it, in which case it is copied and made private before the access.
Copy-on-reference allows sharing of the initial values of a global section whose
pages have read/write access but contain preinitialized data available to many
processes.
copy thread
In terms of volume shadowing, a copy thread is a single stream of I/O that is part
of a full copy or merge operation.
cost
An numeric value assigned to a circuit that exists between two adjacent nodes.
In the DECnet for OpenVMS network, data packets are routed on paths with the
lowest cost.
counted string
A character-string data structure consisting of a byte-sized length followed by the
string. Although a counted string is not used as a procedure argument, it is a
convenient representation in memory.

Glossary–20

counters
Performance and error statistics kept for a network component, such as lines or
nodes.
CPU
See central processing unit.
crash
The system’s response to an unstable condition, particularly if the system is
corrupted. Rather than continuing to operate and possibly damaging itself, the
system stops functioning. If the system has crashed, users will be unable to use
their terminals. See hanging.
crash dump
The action the operating system takes, when it crashes, to preserve information
for future analysis. See complete crash dump and selective crash dump.
CRB
See channel request block.
CRC
See cyclic redundancy check.
CRT
Cathode-ray tube. See terminal.
cross development
The process of creating software using tools running on one system, but targeted
for another type of system. For example: creating AXP code using tools running
on a VAX VMS system.
CSMA/CD
See Carrier Sense, Multiple Access with Collision Detect.
CSR
See control and status register.
CUG
See closed user group.
current access mode
The processor access mode of the currently executing software indicated in the
current mode field of the processor status.
current accounting file
The accounting file in which the local node is currently storing information
about resource use. By default, it is SYS$MANAGER:ACCOUNTNG.DAT. See
accounting file.
cursor
An indicator used on a video terminal to point to the screen position where the
next character will appear.

Glossary–21

cyclic redundancy check (CRC)
An error detection scheme in which the receiver checks each block of data for
errors. The check character is generated by taking the remainder after dividing
all the serialized bits in a block of data by a predetermined binary number. The
check character is compared with the transmitter-generated check character.
If the check characters do not match, retransmission of the block of data is
requested.
cylinder
The tracks at the same radius on all recording surfaces of a disk.
data
A general term referring to any representation of facts, concepts, or instructions
in a form suitable for communication, interpretation, or processing.
database
(1) All the occurrences of data described by a database management system.
(2) A collection of related data structures.
data check
An operation that consists of first performing the derived physical, logical, or
mutual read or write function successfully and then comparing the data in
memory with the data on disk to make sure they match.
data circuit-terminating equipment (DCE)
A CCITT X.25 term referring to the network equipment that establishes,
maintains, and terminates a connection and handles the signal conversion and
coding between the data terminal equipment and the network. The switching
exchange of the network to which data terminal equipment (DTEs) are connected.
In non-X.25 usage, the term is synonymous with ‘‘modem.’’
datagram
A unit of data sent over the network that is handled independently of all other
units of data so far as the network is concerned. When a route header is added, a
datagram becomes a packet.
data integrity
The ability of a system to maintain its information in a consistent state.
data link mapping (DLM)
Capability of using an X.25 virtual circuit as a DECnet for OpenVMS data link.
data terminal equipment (DTE)
An X.25 term referring to the user’s equipment (computer or terminal) connected
to a data circuit-terminating equipment (DCE) on a packet switching data
network (PSDN) for the purpose of sending and receiving data.
data structure
Any table, list, array, queue, or tree whose format and access conventions are
well defined for reference by one or more images.

Glossary–22

data type
In general, the way in which bits are grouped and interpreted. In reference to
the processor instructions, the data type of an operand identifies the size of the
operand and the significance of the bits in the operand. Operand data types
include byte, word, longword, and quadword integer; floating and double-floating
character string; packed decimal string; and variable-length bit field.
DCE
See data circuit-terminating equipment.
DCL
See DIGITAL Command Language.
DDB
See device data block.
DDT
See driver dispatch table.
debugger
A program that aids a programmer in finding errors in other programs.
debug symbol table
The portion of the symbol table that is created by the compiler or assembler.
decryption
The process that restores encrypted information to its original unencoded form.
dedicated resource
A system resource—an I/O device, image, or the entire system—that is assigned
to a single application or purpose.
default
A value or operation that is automatically included in a command, unless the
user specifies otherwise. In most cases, default settings will be what is ‘‘normal’’
or ‘‘expected’’.
default directory
The directory that the operating system assumes when a directory specification
has not been supplied by the user.
default disk
The disk from which the system reads and to which the system writes; by default,
all files that you create. The default disk is used whenever a file specification in
a command does not explicitly name a device.
deferred echo
Refers to the fact that terminal echoing does not occur until a process is ready to
accept input entered by type-ahead.

Glossary–23

degraded performance
Performance in which service continues, but response time is extended or the
number of users that can be served is reduced, or both.
delimiter
A character that separates, terminates, or organizes elements of a character
string, statement, or program.
delta time
A time value expressing an offset from the current date and time. Delta times
are always expressed in the system as negative numbers whose absolute value is
used as an offset from the current time.
demand-zero page
A page, typically of an image stack or buffer area, that is initialized to contain
all zeros when dynamically created in memory as a result of a page fault. This
feature eliminates the waste of disk space that would otherwise be required to
store blocks (pages) that contain only zeros.
density
The number of bits per inch (bpi or bpi/in) of magnetic tape. Typical values are
800 bpi and 1600 bpi. See bits per inch.
dependable computing system
One that can be counted on to provide services to its users when those services
are needed, and with sufficient performance. The computing components are
created and combined in the manner necessary to provide a required level of
dependability.
descriptor
A data structure used in calling sequences for passing argument types, addresses,
and other optional information. See character string descriptor.
designated router
A routing node on the Ethernet selected to perform routing services on behalf of
end nodes.
destructor
A user-supplied routine that finalizes and then deallocates a per-thread context
value.
detached process
A process that has no owner. The job controller creates a detached process when
a user logs in to the system. It also creates a detached process each time it
initiates a batch job or services a request for a logical link connect. Because the
job controller does not own the processes it creates, these processes are referred
to as detached. The DCL command RUN/UIC and the Create Process system
service (specifying a UIC) allow a suitably privileged process to request creation
of a detached process.

Glossary–24

device
The general name for any peripheral connected to the processor that is capable
of receiving, storing, or transmitting data. Card readers, line printers, and
terminals are examples of record-oriented devices. Magnetic tape devices and
disk devices are examples of mass storage devices. Terminal line interfaces and
interprocessor links are examples of communications devices. Devices are not
necessarily hardware (see pseudodevice).
device affinity
In a symmetric multiprocessing system, a close association of a device with a
specific processor or set of processors in the system. There are three dimensions
to device affinity in the operating system. First, physical connectivity describes
those devices that are directly accessible only to the primary processor or
to all processors. Secondly, affinity is a software mechanism that defines
those processors that can initiate an I/O operation on the device. Finally,
interruptibility describes the set of processors that can receive interrupts from a
device.
device allocation
See allocating.
device controller
The electronic circuits associated with each physical device in the system that
serve as the interface between the processor and the device hardware.
device data block (DDB)
A structure in the I/O database that identifies the generic device or controller
name and driver name for a set of devices attached to the same controller.
device driver
The software associated with each physical device in the system that serves as
the interface between the operating system and the device controller.
Device driver code is divided into two sections: device-dependent logic that drives
a particular kind of device unit, and device-independent support routines that
perform functions common to all devices. Each unit of a particular type has a
driver process, but there is only one set of driver code.
device interrupt
An interrupt received on interrupt priority levels (IPLs) 20 through 23. Device
interrupts can be requested only by devices, controllers, and memories.
device lock
In a symmetric multiprocessing system, a dynamic spin lock, the ownership of
which synchronizes device-specific code that executes at device interrupt priority
level (IPL). A device lock is associated with each adapter or controller in the
system. See spin lock.

Glossary–25

device name
The field in a file specification that identifies the device unit on which a file is
stored. Device names also include the mnemonics that identify an I/O peripheral
device in a data transfer request. A device name consists of a mnemonic followed
by a controller identification letter (if applicable), followed by a unit number (if
applicable), and ends with a colon.
device queue
See spool queue.
device register
A location in device controller logic used to request device functions (such as I/O
transfers) or report status.
device unit
An I/O device and its controlling logic; for example, a disk drive or terminal.
Some controllers can have several device units connected to a single controller;
for example, mass storage controllers.
D_floating point data
See double floating data.
diagnostic
A program that tests hardware, firmware, peripheral operation, logic, or memory
and reports any faults it detects.
DIGITAL Command Language (DCL)
A command interpreter in the operating system. It provides a means of
communication between the user and the operating system. See monitor console
routine.
DIGITAL Network Architecture, DNA
A set of protocols (rules) governing the format, control, and sequencing of
message-exchange for all Digital network implementations. The protocols are
layered, and they define rules for data exchange from the physical link level up
through the user interface level. DNA controls all data that travels throughout a
Digital network. DNA also defines standard network management and network
generation procedures.
Digital Storage Architecture (DSA)
The specifications from Digital governing the design of and interface to mass
storage products. DSA defines the functions to be performed by host computers,
controllers, and drives, and specifies how they interact to manage mass storage.
Digital Storage Systems Interconnect (DSSI)
A data bus that uses the System Communication Architecture (SCA) protocols for
direct host-to-storage communications. The DSSI cable can extend to 6 meters
and has a peak bandwidth of 4 megabytes.
direct data path
A UNIBUS adapter data path that transfers 16 bits of data in a single
synchronous backplane interconnect (SBI) transfer.

Glossary–26

direct I/O
An I/O operation in which the system locks the pages containing the associated
buffer in physical memory for the duration of the I/O operation. The I/O transfer
takes place directly from the process buffer. See buffered I/O.
direct mapping cache
A cache organization in which only one address comparison is needed to locate
any data in the cache because any block of main memory data can be placed in
only one possible position in the cache. See fully associative cache.
direct memory access (DMA)
The method by which a device driver transfers a large amount of data without
requesting an interrupt after transferring each of the smaller amounts.
directory
A file that briefly catalogs a set of files stored on disk or tape. The directory
includes the name, type, and version number of each file in the set, as well as a
unique number that identifies the file’s actual location and points to a list of its
attributes. See master file directory and subdirectory.
directory name
The field in a file specification that identifies the directory in which a file is listed.
The directory name begins with a left bracket ([ or <) and ends with a right
bracket (] or >).
disconnect abort
A form of disconnection by which nontransparent tasks can deaccess a logical
link without deassigning the channel. A disconnect abort indicates that not all
messages sent have necessarily been received.
discretionary controls
Security controls that are applied at the user’s option; that is, they are not
required. Access control lists are typical of such optional security features.
disk
High-speed, random-access devices. There are several kinds of disks. Floppy
disks are small, flexible disks. Hard disks are either fixed in place or removable.
Removable disk types include a single hard disk enclosed in a protective case and
a stacked set of disks enclosed in a protective case.
disk scavenging
Any method of obtaining information from a disk that the owner intended to
discard. The information, although no longer accessible by normal means, retains
a sufficient amount of its original magnetic encoding so that it can be retrieved
and used by one of the scavenging methods.
distributed transaction processing
The processing of transactions on remote nodes. A user logged in to a transaction
processing system on one node can select tasks in an application on a transaction
processing system on another node.

Glossary–27

DLM
See data link mapping.
DMA
See direct memory access.
DNA
See DIGITAL Network Architecture.
double floating data
A double precision floating-point number, eight bytes long, having a range of
62:9 3 10037 to 61:7 3 1038 and a precision of approximately 16 decimal digits. See
G_floating data.
downline system load
A DECnet for OpenVMS function that allows an unattended target node to
receive an operating system file image or terminal server image from another
node.
downline task load
A DECnet for OpenVMS function that allows a remote target node to receive an
RSX–11S task from another node.
down time
The percentage or amount of time a computing system does not provide
application service as scheduled.
DPT
See driver prolog table.
drive
The electromechanical unit of a mass storage device system on which a recording
media (disk cartridge, disk pack, or magnetic tape reel) is mounted.
driver
See device driver.
driver code
See device driver.
driver dispatch table (DDT)
A table in a driver that lists the entry point addresses of standard driver routines
and the sizes or diagnostic and error logging buffers for the device type.
driver fork level
The interrupt priority levels (IPLs) at which a driver fork processes executes,
that is, IPLs 8 through 11. Every unit control block indicates the address of a
fork lock that synchronizes driver resources. The fork lock structure indicates the
fork level or driver.

Glossary–28

driver prolog table (DPT)
A table in the driver that describes the driver and the device type to the
procedure that loads drivers into the system.
driver start I/O routine
See start I/O routine.
DSA
See Digital Storage Architecture.
DSSI
See Digital Storage Systems Interconnect.
DST
See debug symbol table.
DTE
See data terminal equipment.
DV
The bit in the processor status word that indicates that decimal overflow traps
are enabled.
dynamic access
A technique in which a program switches from one record access mode to another
while processing a file.
dynamic load balancing
A method of work distribution in which the operating system ensures that
the system work load is evenly distributed among the processors. Dynamic
load balancing in a symmetric multiprocessing system is a direct effect of
the implementation of the scheduler. In a multiprocessing system, processors
independently and continually look for processes to execute from a common pool
of processes.
EBCDIC
See Extended Binary Coded Decimal Interchange Code.
ECB
See exit control block.
ECC
See error correction code.
echo
A terminal handling characteristic in which the characters typed by the user on
the terminal keyboard are also displayed on the screen or printer.
editor
A system image used for creating and altering text files.

Glossary–29

effective address
The address obtained after deferred or indexing modifications are calculated.
encryption
A process of encoding information so that its content is no longer immediately
obvious to anyone who obtains a copy of it.
end node
A node that can receive packets addressed to it and send packets to other nodes,
but cannot route packets through from other nodes. Also called a nonrouting
node.
entry mask
On VAX systems, a word whose bits represent the registers to be saved when a
procedure is called with a CALLS or CALLG instruction, and restored when the
procedure executes a RET instruction.
entry point
A location that can be specified as the object of a call.
environmental identifier
One of four classes of identifiers. Environmental identifiers are provided by
the system to identify groups of users according to their usage of the system.
For example, all users who access the system by dialing up receive the Dialup
identifier. See identifier.
equivalence name
The string associated with a logical name in a logical name table. An equivalence
name can be, for example, a device name, another logical name, or a logical name
concatenated with a portion of a file specification. See search list.
erase-on-allocate
A technique that applies an erasure pattern whenever a new area is allocated
for a file’s extent. The new area is erased with the erasure pattern so that
subsequent attempts to read the area can only yield the erasure pattern and
not some valuable remaining data. This technique is used to discourage disk
scavenging.
erase-on-delete
A technique that applies an erasure pattern whenever a file is deleted or purged.
This technique is used to discourage disk scavenging.
erasure pattern
A character string that can be used to overwrite magnetic media for the purpose
of erasing the information that was previously stored in that area.
error
An event during the operation of a computing component that produces incorrect
results due to one or more faults. Errors are observed as incorrect responses
within a specific computing component.

Glossary–30

error correction
The action necessary to isolate the effects of faults to a specific computing
component. The goal is to contain the impact of the problem.
error correction code (ECC)
Code that carries out automatic error correction by performing an exclusive OR
operation on the transferred data and applying a correction mask.
error logger
A system process that empties the error log buffers and writes the error messages
into the error file. Errors logged by the system include memory system errors,
device errors and timeouts, and interrupts with invalid vector addresses.
error message
Sent by the system when some action you have requested fails. Each error
message identifies the particular part that detected the error. Most error
messages result from typing mistakes or syntax mistakes. Often, you can correct
the error by retyping the command.
escape sequence
An escape is a transition from the normal mode of operation to a mode outside
the normal mode. An ASCII escape character is the code that indicates the
transition from normal to escape mode. An escape sequence refers to the set
of character combinations starting with an escape character that the terminal
transmits without interpretation to the software set up to handle escape
sequences.
ESP
See executive-mode stack pointer.
ESR
See exception service routine.
Ethernet
A communications concept for local communication networks that employs
coaxial cable as a passive communications media to interconnect different kinds
of computers, information processing products, and office equipment at a local
business site. Ethernet does not require switching logic or control by a central
computer.
evasive action
A responsive behavior by the system to discourage break-in attempts whenever
they seem to be in progress. The system has a set of criteria it uses to detect the
fact that break-in attempts may be underway. Typically, once the system suspects
that an unauthorized user is attempting to log in, the evasive action consists of
locking out all login attempts by the offender for a limited period of time.

Glossary–31

event
(1) A change in process status or an indication of the occurrence of some activity
that concerns an individual process or cooperating processes; an incident
reported to the scheduler that affects a process’s ability to execute. Events
can be synchronous with the process’s execution (a wait request), or they can
be asynchronous (I/O completion). Some other events include swapping, wake
request, and page fault.
(2) A network or system-specific occurrence for which the logging component
maintains a record.
(3) An exception or interrupt.
event class
A particular classification of events. Generally, this classification follows the
DIGITAL Network Architecture, or DNA architectural layers; some layers
may contain more than one class. Class also includes the identification of
system-specific events.
event flag
A bit in an event-flag cluster that can be set or cleared to indicate the occurrence
of the event associated with that flag. Event flags are used to synchronize
activities in a process or among many processes.
event-flag cluster
A set of 32 event flags used for event posting. Four clusters are defined for each
process: two process-local clusters and two common event flag clusters. Of the
process-local flags, eight are reserved for system use.
event type
A particular form of event that is unique within an event class.
exception
An event detected by the hardware or software (other than an interrupt
or jump, branch, case, or call instruction) that changes the normal flow of
instruction execution. An exception is always caused by the execution of an
instruction or set of instructions (whereas an interrupt is caused by an activity
in the system independent of the current instruction). There are three types
of hardware exceptions: traps, faults, and aborts. Examples are attempts to
execute a privileged or reserved instruction, trace traps, compatibility mode
faults, breakpoint instruction execution, and arithmetic traps such as overflow,
underflow, and division by zero.
exception dispatcher
An operating system procedure that searches for a condition handler when an
exception condition occurs. If no exception handler is found for the exception or
condition, the image that incurred the exception is terminated.
exception enables
See trap enables.

Glossary–32

exception service routine (ESR)
The routine by which VAX and AXP hardware initially pass control to service
an exception. An exception service routine passes control to a general exception
dispatcher that attempts to locate a condition handler to further service the
exception.
exception vector
See vector.
executable image
An image that can be run in a process. When run, an executable image is read
from a file for execution in a process.
executive
The generic name for the collection of procedures included in the operating
system software that provides the operating system’s basic control and monitoring
functions.
executive mode
The second most privileged processor access mode (mode 1). The OpenVMS
Record Management Services (RMS) and many of the operating system’s system
service procedures execute in executive mode.
executive-mode stack pointer (ESP)
The process context stack pointer for executive mode.
executor node
The node at which a Network Control Program (NCP) command actually
executes.
exit
An image rundown activity that occurs when image execution terminates
either normally or abnormally. Image rundown activities include deassigning
I/O channels and disassociating common event flag clusters. Any user- or
system-specified exit handlers are called.
exit control block (ECB)
A data structure that describes an exit handling routine declared by the Declare
Exit Handler system service, $DCLEXH.
exit handler
A procedure executed when an image exits. An exit handler enables a procedure
that is not on the call stack to gain control and clean up procedure-owned
databases before the actual image exit occurs.
expression
Any combination of variables and/or constants with operators that the computer
can evaluate to produce a result.

Glossary–33

extended attribute block (XAB)
A OpenVMS Record Management Services (RMS) user data structure that
contains additional file attributes beyond those expressed in the file access block
(FAB), such as boundary types (aligned on cylinder, logical block number, and
virtual block number) and file protection information.
Extended Binary Coded Decimal Interchange Code (EBCDIC)
A set of 8-bit characters used for representing data. See ASCII.
extended QIO processor (XQP)
A facility that supplements the QIO driver’s functions when performing virtual
I/O operations on file-structured devices (Files–11 On-Disk Structure Level 2).
The XQP executes in kernel mode in the context of the process of its caller.
extension
The amount of space allocated at the end of a file each time a sequential write
exceeds the allocated length of the file.
extent
The contiguous area on a disk containing a file or a portion of a file. An extent
consists of one or more clusters.
F11ACP
See Files–11 ancillary control process.
FAB
See file access block.
failover
(1) The process of reconfiguration after a hard fault or for planned maintenance.
(2) The ability of a system or component to reconfigure itself.
failure
The inability of a computing component to perform its function correctly due
to one or more internal faults whose effects cannot be contained. Failures are
observed as incorrect behavior by the consumers of the computing component’s
services.
failure exception mode
A mode of execution selected by a process that instructs the system to declare
an exception condition if an error occurs as the result of a system service call.
The normal mode is for the system service to return a status code for which the
process must test.
failure recovery
The action necessary to restore the failed computing component to a correctly
functioning condition. The goal is prompt return to zero defects.

Glossary–34

fallback
A function that the Terminal Fallback Facility (TFF) performs when an
application program sends a character that a terminal cannot display. In this
case, TFF replaces the character with the closest possible visual character that
the terminal can display.
fault
(1) A hardware exception condition that occurs in the middle of an instruction
and leaves the registers and memory in a consistent state so that eliminating the
fault and restarting the instruction gives correct results.
(2) A defect in some component of a computing system.
fault management
The discipline used to engineer systems with a cost-effective balance of fault
prevention qualities, error correction capabilities, and failure recovery facilities.
Fault management is realized in the implementation of a dependable computing
system. It is also a philosophy that is followed during the implementation.
fault prevention
The process of designing and constructing computing components to be free from
faults. The goal is zero defects.
fault tolerance
(1) The ability of a computing system to sustain a single operational fault while it
continues to provide service without user intervention, with no significant delay
in service, without loss of work in progress, and with complete data integrity.
(2) The ability of a computing system to withstand faults and errors while
continuing to provide the required services. See hardware-based fault tolerance
and software-based fault tolerance.
FCB
See file control block.
FCS
See file control system.
FDL
See file definition language.
FDT
See function decision table.
FDT routine
A driver routine called by the Queue I/O Request system service to perform
device-dependent preprocessing of an I/O request.
F_floating-point data
See floating (point) data.
FID
See file identifier.

Glossary–35

field
A set of contiguous bytes in a logical record. See variable-length bit field.
FIFO
First-in/first-out; the order in which processing is performed. For example,
processing on a FIFO queue would be on a first-come, first-served basis. See
LIFO.
file
A set of data elements arranged in a structure significant to the user. A file is
any named, stored program or data, or both, to which the system has access.
Access can be of two types: read-only, meaning the file is not to be altered, and
read-write, meaning the contents of the file can be altered. See volume.
OpenVMS security policy protects files from improper access. An operation can
require read, write, execute, delete, or control access.
file access block (FAB)
A OpenVMS Record Management Services (RMS) user data structure that
describes a particular file and contains file-related information needed for data
operations, such as OPEN, CLOSE, or CREATE.
file control block (FCB)
A memory-resident structure used by the operating system to coordinate access to
a file that is opened by an active task.
file control system (FCS)
A generic term for the file control services that control the file services for disks
and tapes. These services include adding, opening, closing, and renaming files.
file definition language (FDL)
A special-purpose language used to write specifications for data files. These
specifications are written in text files called FDL files; they are then used by
OpenVMS Record Management Services (RMS) utilities and library routines to
create the actual data files.
file header
A block in the index file describing a file on a Files–11 disk structure. The file
header contains information needed by the file system to find and use the file.
Some of this information is displayed when the DCL command DIRECTORY is
entered. There is at least one file header for every file on the disk.
file identifier (FID)
A 6-byte value used to uniquely identify a file on a Files–11 disk volume. The file
number, file sequence number, and relative volume number are contained in the
file identifier.
file name
The field containing a 1- to 39-character name for a file that precedes a file type
in a file specification.
file name extension
See file type.

Glossary–36

file organization
The particular file structure used as the physical arrangement of the data
comprising a file on a mass storage media. The OpenVMS Record Management
Services (RMS) file organizations are sequential, relative, and indexed.
Files–11
The name of the disk structure used by the RSX–11, IAS, and OpenVMS
operating systems. See Files–11 On-Disk Structure Level 1 and Files–11 On-Disk
Structure Level 2.
Files–11 ancillary control process (F11ACP)
The interface process that is the files manager for the Files–11 on-disk structure.
Files–11 On-Disk Structure Level 1
The original Files–11 structure used by IAS, RSX–11M, and RSX–11S for disk
volumes. VAX systems support structure level 1 to ensure compatibility among
systems. AXP systems do not support structure level 1.
Files–11 On-Disk Structure Level 2
The second-generation disk file structure supported by The operating system.
The Files–11 data structure prepares a volume to receive and store data in a way
recognized by the operating system.
file section
The part of a file that contains the user data and that is delimited by the header
and trailer labels. Only one section of a given file can be written on any one
volume. Multiple sections of a file or other file sections cannot be interspersed
within a file section.
file sharing
The capability of a particular relative or indexed file to allow access to more than
one process.
file specification
A unique name for a file on mass storage media. It identifies the node, the device,
the directory name, the file name, the file type, and the version number under
which a file is stored.
file structure
The way in which the blocks forming a file are distributed on a disk or magnetic
tape.
file system
A method of recording, cataloging, and accessing files on a volume.
file type
The field in a file specification that consists of a period followed by a 0- to
39-character identification. By convention, this field identifies a generic class of
files that have the same use or characteristics, such as compiler and assembler
listing files, binary object files, and so on.

Glossary–37

first part of an instruction done (FPD)
On VAX systems, a bit in the processor status longword. If the FPD is set, when
the processor returns from an exception or interrupt, it resumes the interrupted
operation where it left off, rather than restarting the instruction.
fixed-length control area
An area, prefixed to a variable-length record, containing additional information
about the record that may have no bearing on the other contents of the record.
The fixed-length control area may be used, for example, to contain line numbering
or carriage control information.
fixed-length record format
A file format in which all records have the same length.
fixed line number
A number fixed to a line of text in a file. The EDT text editor maintains a record
of line numbers during the editing sessions in which the files are used; they are
copied to the file when the editing session ends.
flag
A bit that can be set to invoke the execution of a particular sequence of
instructions; frequently, an indicator used to tell some later part of a program
that a certain condition occurred earlier.
floating (point) data
A single precision floating-point number, 4 bytes long, having a range of
62:9 3 10037 to 61:7 3 1038 and a precision of approximately seven decimal digits.
floating point register
On AXP systems, any of the 32 32-bit registers used to manipulate a floatingpoint operand, to pass a floating-point argument, or to return a floating-point
function value.
floating underflow (FU)
On VAX systems, a trap enable bit in the processor status word (PSW).
folder
A subdivision of a file in which you can store mail messages.
foreign command
A symbol that executes an image whose name is not recognized by the command
interpreter as a DCL command.
foreign file specification
A file whose specification does not conform to the OpenVMS oerating system
syntax.
foreign volume
Any volume other than a Files–11 formatted volume. A foreign volume may or
may not be file-structured.

Glossary–38

fork block
The portion of a unit control block that contains a driver’s context while the
driver is waiting for a resource, or the portion of another structure used as a fork
block to enable the driver to synchronize events at a lower interrupt priority level
(IPL). A driver awaiting a processor or adapter resource has its fork block linked
into a fork queue.
fork dispatcher
An interrupt service routine that is activated by a software interrupt at a fork
interrupt priority level (IPL). Once activated, it dispatches driver fork processes
from a processor-specific fork queue until no processes remain in the queue for
that IPL.
fork lock
In a OpenVMS symmetric multiprocessing system, a static spin lock, the
ownership of which synchronizes the right of a driver’s fork process to execute at
its associated fork interrupt priority level (IPL). See spin lock.
fork process
A minimal context process that executes code under a series of constraints: it
executes at raised interrupt priority levels; it uses R0 through R5 only (other
registers must be saved and restored); it executes in system virtual address
space; it is only allowed to refer to and modify static storage that is never
modified by higher interrupt priority level code. The operating system uses
software interrupts and fork processes to synchronize executive operations.
fork queue
A processor-specific queue of driver fork blocks that is awaiting activation, at a
particular interrupt priority level, by the fork dispatcher.
form feed
The movement of the cursor position to the start of a new page.
FP
See frame pointer and stack frame base register.
FPD
See first part of an instruction done.
frame
A unit, which is delimited by flags and includes a header, used by the link level
to exchange data packets as well as control and error information between data
terminal equipment (DTE) and data circuit-terminating equipment (DCE) on a
packet switching data network. See stack frame.
frame pointer (FP)
On VAX systems, general register 13 (R13); on AXP systems, integer register
(R29). By convention, it contains the base address of the most recent call frame
on the stack.

Glossary–39

front-end
The part of a computing system that typically handles data capture, terminal
displays, communications, and validation functions.
FU
See floating underflow.
full copy assist
Optimizes performance during a volume shadowing full copy operation. The full
copy assist decreases the impact on the system, the I/O bandwidth consumption,
and the time required for full copy operations by allowing the host node to control
a direct disk-to-disk transfer of data.
full copy member
A device that is not yet a member of the shadow set, but that is being added
to the shadow set and requires a full copy operation because it is completely
inconsistent with respect to the other members in the shadow set.
full copy operation
Copies data from an active shadow set member to a new, specified volume
in order to make the new device consistent and bring it into full shadow set
membership. The specified volume should be a blank volume or a former shadow
set member that is not consistent with the other shadow set members.
fully associative cache
A cache organization in which any block of data from main memory can be placed
anywhere in the cache. Address comparison must take place against each block
in the cache to find any particular block. See direct mapping cache.
function code
See I/O function code.
function decision table (FDT)
A table in a device driver that lists all valid function codes for the device and the
addresses of I/O preprocessing routines associated with each valid function.
function keys
Keyboard keys that send special signals to the operating system. Function
keys are referred to as Fx, where x is the number associated with that key. For
example, when you enter a DCL command and press F12, you are telling the
system to move the cursor to the beginning of the line.
function modifier
See I/O function modifier.
general identifier
One of three possible types of identifiers that specify one or more groups of
users. The general identifier is alphanumeric and typically is a convenient term
that symbolizes the nature of the group of users. For example, a typical general
identifier might be PAYROLL for all users allowed to run payroll applications.

Glossary–40

general purpose register
Any of the registers designated by the processor architecture to be used as the
primary operands of native-mode instructions. The general registers include
general-purpose registers, which can be used as accumulators, as counters, and
as pointers to locations in main memory.
The VAX architecture provides 16 32-bit general purpose registers, R0 through
R12, including the frame pointer, argument pointer, stack pointer, and program
counter.
The 32 32-bit AXP integer registers, R0 through R31, include registers with
designated special purposes like the stack pointer, frame pointer, argument info
register, return address register, and procedure value register.
generic device name
A device name that identifies the type of device but not a particular unit; a device
name in which the specific controller or unit number is omitted.
G_floating data
An extended-range floating-point number, 8 bytes long, having a range of
60:56 3 100308 to 60:9 3 10308 and a precision of approximately 15 decimal digits.
global
Affecting the entire file, the entire system, or the entire image, depending on
context. A global substitution in a text file would be the changing of all instances
of a particular string to something else, for example, changing ‘‘dog’’ to ‘‘cat.’’
global page table
The page table containing the master page table entries for global sections.
global section
A shared memory area (for example, FORTRAN global common) potentially
available to all processes in the system. Access is protected by standard access
control mechanisms.
global symbol
(1) A symbol defined in a module of a program that is potentially available
for reference by another module. The linker resolves (matches references with
definitions) global symbols. See local symbol.
(2) A command language symbol accessible at all command levels.
global symbol table (GST)
In a library, an index of strongly defined global symbols used to access the
modules defining the global symbols. The linker also puts global symbol tables
into an image. For example, the linker appends a global symbol table to
executable images that are intended to run under the symbolic debugger, and it
appends a global symbol table to all shareable images.
Gold key
The upper-left key on the VT100 series terminal keypad, which enables alternate
keypad functions.

Glossary–41

granularity
A characteristic of storage systems that defines the amount of data that can be
read or written with a single instruction, or read or written independently. VAX
systems have byte or multibyte granularities while disk systems typically have
512-byte or greater granularities. AXP systems have longword and quadword
granularities.
group
(1) A set of users in a system. The group name appears as the first field of
a user identification code (UIC): [group,member]. The access rights accorded
the group member appear in the third field of an object’s protection code:
(System:access,Owner:access,Group:access,World:access).
(2) A set of jobs (processes and their subprocesses) with access to a group’s
common event flags and logical name tables.
group number
The number or its alphanumeric equivalent in the first field of a user
identification code (UIC).
GST
See global symbol table.
handshaking sequence
The exchange of logical link connection information between two tasks. This
exchange takes place to enable the successful completion of a logical link
connection.
hanging
The extremely slow response of the system. During an interactive session, when
the terminal fails to respond, it is said to be hanging. When the system hangs,
users might think that it has crashed.
hardcopy terminal
Terminals that print output on paper. See terminal.
hardware
The physical computer equipment, including such mechanical devices as the line
printer, the terminals, the mass-storage devices, and so forth.
hardware address
For an Ethernet device, the unique Ethernet physical address associated with a
particular Ethernet communications controller (usually in read-only memory) by
the manufacturer.
hardware-based fault tolerance
The ability to detect, isolate, and bypass a fault that has been engineered into
and executed through hardware.

Glossary–42

hardware context
The values contained in the processor registers while a process is executing.
When a process is executing, its hardware context is continually being updated by
the processor. When a process is not executing, its hardware context is stored in
its hardware process control block (PCB) on the VAX system, and the hardware
privileged context block (HWPCB) and other software data structures on AXP
systems.
hardware exception
A particular category of exceptions that directly reflect an exceptional condition
in the current hardware state that should be noted or fixed by the software.
Hardware exceptions may occur synchronously or asynchronously with respect to
the normal program flow.
hardware privileged context block (HWPCB)
On AXP systems, a data structure known to the processor that contains the saved
privileged context when a process is not executing. A process’s HWPCB resides in
its process header.
hardware process control block (hardware PCB)
On VAX systems, a data structure known to the processor that contains the saved
hardware context when a process is not executing. A process’s hardware PCB
resides in its process header.
header page
Printed page at the beginning of a listing that identifies the printed file.
help file
A text file in a format suitable for use with the HELP command. Help files can
provide up to nine levels of search.
H_floating data
An extended range floating-point number, 16 bytes long, having a range of
60:84 3 1004932 to 60:59 3 104932 and a precision of approximately 33 decimal
digits.
hibernation
A state in which a process is inactive, but known to the system. A hibernating
process becomes active again when a wake request is issued. It can schedule a
wake request before hibernating, or another process can issue its wake request.
A hibernating process can also become active long enough to service any AST it
may receive while it is hibernating. See suspension.
hierarchical directory structure
A structure of directories that has several levels arranged in a tree-like structure,
based on a one-to-many relationship.
hierarchical storage controller, HSC
A self-contained, intelligent, mass-storage controller that communicates with VAX
processors and implements volume shadowing on Digital Storage Architecture
(DSA) disks.

Glossary–43

high-level language
A language for specifying computing procedures or organization of data within
a digital computer. High-level languages are distinguished from assembly and
machine languages by the omission of machine-specific details required for direct
execution on a given computer.
highwater marking
A technique for discouraging disk scavenging. The system tracks the furthest
extent that the owner of a file has written into the file’s allocated area. It then
prohibits any attempts at reading beyond the written area on the premise that
any information that exists beyond the currently written limit is information
some user had intended to discard. The operating system accomplishes the goals
of highwater marking with its erase-on-allocate strategy.
holder
A user who possesses a particular identifier. Users and the identifiers they hold
are recorded in the rights database. Whenever an object requires an accessor to
hold an identifier, the system checks the process rights list (which is built from
the rights database) in processing the access request.
home block
A block in the index file that contains the volume identification, such as volume
label and protection.
hop
The logical distance between two nodes. One hop is the distance from one node to
an adjacent node.
host node
(1) For a DECnet for OpenVMS network, a node that provides services for
another node (for example, the host node supplies program image files for a
downline load). For the VAX Packetnet System Interface (PSI), a node that
accesses a packet switching data network by means of an X.25 multihost
connector node.
(2) The node that makes a device available to other nodes in a VMScluster
configuration. A host node can be either a processor that adds the device to the
mass storage control protocol (MSCP) server database or a hierarchical storage
controller (HSC) server.
hot standby
A second running computing system that is ready to pick up application
processing in the event the primary computing system fails.
HSC
See hierarchical storage controller.
HWPCB
See hardware privileged context block.
IDB
See interrupt dispatch block.

Glossary–44

identifier
An alphanumeric string representing a user or group of users that is stored in the
rights database and used by the system in checking access requests. There are
four types of identifiers: user identification code (UIC) identifiers, environmental
identifiers, general identifiers, and facility identifiers.
image
Procedures and data bound together by the linker to form an executable program.
This executable program is executed by the process. There are three types of
images: executable, shareable, and system.
image activator
A set of system procedures that prepares an image for execution. The image
activator establishes the memory management data structures required both to
map the image’s virtual pages to physical pages and to perform paging.
image exit
See exit.
image information file (IIF)
An ASCII file that contains information about the interface between VAX system
images. VAX Environment Software Translator (VEST) uses IIFs to resolve
references to other images and to generate the appropriate linkages. VEST is
part of the DECmigrate tool set.
image I/O segment
That portion of the control region that contains the OpenVMS Record
Management Services (RMS) internal file access blocks (IFAB) and I/O buffers for
the image currently being executed by a process.
image name
The name of the file in which an image is stored.
image privileges
The privileges assigned to an image when it is installed. See process privileges.
image section
A group of program sections with the same attributes (such as read-only access,
read/write access, absolute, relocatable, and so on) that is the unit of virtual
memory allocation for an image.
immediate value
A mechanism for passing input parameters where the actual value is provided in
the argument list entry by the calling program.
inbound connection
Logical link connection requests that a task receives.
increment
(1) To add one quantity to another.
(2) The quantity added.

Glossary–45

index
The structure that allows retrieval of records in an indexed file by key value. See
key (indexed files).
indexed file organization
A file organization in which a file contains records and a primary key index
(and optionally one or more alternate key indexes) used to process the records
sequentially by index or randomly by index.
indexed sequential file
A record file in which each record has one or more data keys embedded in it.
Records in the file are individually accessible by specifying a key associated with
the record.
index file
The file on a Files–11 volume that contains the access information for all files on
the volume and enables the operating system to identify and access the volume.
index file bitmap
A table in the index file of a Files–11 volume that indicates which file headers are
in use.
indirect command file
See command procedure.
input file
File containing data to be transferred into the computer.
Often input and output files are confused. DCL usually prompts for these files,
but most system utilities require you to identify your input and output files by
position in a command line. Be sure of the syntax for the command you are
using.
input stream
The source of commands and data—the user’s terminal, the batch stream, or a
command procedure.
integer register
See general purpose register.
integrated storage element (ISE)
A disk or tape device that contains a dedicated controller for the device in a
combined package. The ISE contains fully functional MSCP/TMSCP server
components, SCS, and port interface logic. ISEs are intelligent multi-host
controllers, and work in parallel with other ISEs on the interconnect.
interactive
Mode of communication with the operating system in which you enter a
command, and the system executes it and responds. One command has to finish
executing before you can enter another.

Glossary–46

interactive system
A computer system in which the user and the operating system communicate
directly by means of a terminal. The operating system immediately acknowledges
and acts upon requests entered by the user at the terminal.
interactive utility
A computer program, invoked with a DCL command, that provides a special
environment from which you can perform a specific set of tasks. You work
interactively with these utilities by entering subcommands and other information
in response to the utility’s prompt.
interleaving
Assigning consecutive physical memory addresses alternately between two
memory controllers.
interlocked instruction
A VAX instruction that performs some action in a way that guarantees the
complete result as a single, uninterruptible operation in a multiprocessing
environment. Since other potentially conflicting operations can be blocked
while the interlocked instruction completes, interlocked instructions can have a
negative performance impact.
interprocess communication facility
A common event flag cluster, mailbox, or global section used to pass information
between two or more processes.
interrecord gap (IRG)
A blank space deliberately placed between data records on the recording surface
of a magnetic tape.
interrupt
(1) An event other than an exception or a branch, jump, case, or call instruction
that changes the normal flow of instruction execution. Interrupts are generally
external to the process executing when the interrupt occurs. See device interrupt,
software interrupt, and urgent interrupt.
(2) A packet, sent through a packet switching data network, that bypasses normal
flow control procedures used by data packets.
interrupt dispatch block (IDB)
A structure in the I/O database that describes the characteristics of a particular
controller and points to devices attached to that controller.
interrupt message
A user-generated message sent outside the normal exchange of data messages
during nontransparent DECnet for OpenVMS task-to-task communication.
This use of the term interrupt is contrary to the normal usage, which means to
designate a software or hardware interrupt mechanism.

Glossary–47

interrupt priority level (IPL)
The interrupt level at which a software or hardware interrupt is generated.
There are 31 possible interrupt priority levels: IPL 1 is lowest, 31 is highest. The
levels arbitrate contention for processor service. For example, a device cannot
interrupt a processor if the processor is currently executing at an interrupt
priority level equal to or greater than the interrupt priority level of the device’s
interrupt service routine.
interrupt service routine (ISR)
The routine executed when an interrupt occurs.
interrupt stack (IS)
On VAX systems, the processor-specific stack used when executing in interrupt
service context. At any time, the processor is either in a process context executing
in user, supervisor, executive, or kernel mode, or in interrupt service context
operating in kernel mode, as indicated by the interrupt stack and current mode
bits in the processor status longword. The context of the interrupt stack is not
switched.
interrupt stack pointer (ISP)
On VAX systems, the stack pointer for the systemwide interrupt stack.
interrupt vector
See vector.
I/O database
A collection of data structures that describes I/O requests, controllers, device
units, volumes, and device drivers in a system. Examples are the driver dispatch
table, driver prolog table, device data table, unit control block, channel request
block, I/O request packet, and interrupt dispatch block.
I/O driver
See device driver.
I/O function
An I/O operation interpreted by the operating system and typically resulting in
one or more physical I/O operations.
I/O function code
A 6-bit value specified in a Queue I/O Request system service that describes the
particular I/O operation to be performed (for example, read, write, rewind).
I/O function modifier
A 10-bit value specified in a Queue I/O Request system service that modifies an
I/O function code (for example, read terminal input no echo).
I/O lockdown
The state of a page when it cannot be paged or swapped out of memory.

Glossary–48

I/O request packet (IRP)
A structure in the I/O database that describes an individual I/O request. The
Queue I/O Request system service creates an I/O request packet for each I/O
request. The operating system and the driver of the target device use information
in the I/O request packet to process the request.
I/O rundown
An operating system function in which the system cleans up any I/O in progress
when an image exits.
I/O space
The region of physical address space that contains the configuration registers,
and device control and status and data registers. These regions are not physically
contiguous.
I/O status block (IOSB)
A data structure associated with the Queue I/O Request system service. This
service optionally returns a status code, number of bytes transferred, and deviceand function-dependent information in an IOSB. An IOSB is not returned from
the service call, but filled in when the I/O request completes.
IPL
See interrupt priority level.
IRG
See interrecord gap.
IRP
See I/O request packet.
IS
See interrupt stack.
ISE
See integrated storage element.
ISECT
See image section.
ISP
See interrupt stack pointer.
ISR
See interrupt service routine.
iterative translation
Repetitive translation of a logical name that occurs when a logical name’s
definition includes another logical name.
IV
Integer overflow trap enable bit in the processor status word.

Glossary–49

jacket routine
A procedure that converts procedure calls from one calling standard to another,
for example, calls between translated OpenVMS VAX images, which use the VAX
calling semantics, and native AXP images, which use the AXP calling semantics.
JIB
See job information block.
job
The accounting unit equivalent to a process and its subprocesses, if any, and all
subprocesses that they create. Jobs are classified as batch and interactive. For
example, the job controller creates an interactive job to handle a user’s requests
when the user logs in to the system, and it creates a batch job when the symbiont
manager passes a command input file to it.
job controller
The system process that establishes a job’s process context, starts a process
running the LOGIN image for the job, maintains the accounting record for the
job, manages symbionts, and terminates a process and its subprocesses.
job information block (JIB)
A data structure associated with a job that contains the quotas pooled by all
processes in the job.
job tree
A hierarchy of all processes and subprocesses, with the main process at the top.
journal
Name of the auditing log file where the system records events with security
implications, such as logins, breakins, or changes to the authorization database.
journal file
A file containing the data input to the terminal for one editing session.
journaling
The recording of input during an editing session.
K
A unit for measuring the size of memory or similar resources. K is short for kilo
and is used to mean roughly 1000, although K is equal to 210 , or 1024.
kernel mode
The most privileged processor access mode (mode 0). The operating system’s most
privileged services, such as I/O drivers and the pager, run in kernel mode.
kernel-mode stack pointer (KSP)
The process context stack pointer for kernel mode.

Glossary–50

key
(1) In indexed files, a character string, a packed decimal number, a 2- or 4-byte
unsigned binary number, or a 2- or 4-byte signed integer within each data record
in an indexed file. The user defines the length and location within the records;
RMS uses the key to build an index. See primary key, alternate key, and random
access by key value.
(2) In relative files, the relative record number of each data record in a data file;
OpenVMS Record Management Services (RMS) uses the relative record numbers
to identify and access data records in a relative file in random access mode. See
relative record number.
(3) In the Sort utility, the data field in a record that contains the information
required to sort the records.
keyboard
An input device that can be operated similarly to a typewriter.
keypad
The small set of keys next to the main keyboard on a terminal.
keyword
A word reserved for use in certain specified syntax formats, usually in a command
string or a statement.
known component
The classification for one or more of the same DECnet for OpenVMS components.
This classification includes all active and inactive occurrences of the component
type. For example, known nodes include all active and inactive nodes in the
network.
KSP
See kernel-mode stack pointer.
label
A record that identifies and delimits a magnetic tape volume or file section.
label group
A collection of one or more contiguous label sets.
label identifier
The first three characters of a label name, which identify one or more labels
within a label set. These characters will always be the same; for example, a file
identifier of HDR will always be used to identify header labels within a header
label set.
label number
A number that indicates the position of a label within a label set. For ANSI
labels, label number 1 is always present if the label set exists.
label set
One or more contiguous labels on a magnetic tape volume or file section with the
same label identifier.

Glossary–51

language support procedure
A procedure implicitly called to implement higher-level language constructs.
Such procedures are not intended to be explicitly called from user programs.
LAP
See link access protocol.
LAT
See local area transport.
LBN
See logical block number.
LCN
See logical channel number.
level 1 router
A DECnet for OpenVMS node that can send and receive packets, and route
packets from one node to another node within a single area.
level 2 router
A DECnet for OpenVMS node that can send and receive packets, and route
packets from one node to another within its own area and between areas. See
area router.
lexical function
A command language construct that the DIGITAL Command Language (DCL)
command interpreter evaluates and substitutes before it parses a command
string. Lexical functions return information about the current process (the user
identification code [UIC] or default directory, for example) and about character
strings, (their length or the location of substrings, for example).
librarian
A program that allows the user to create, update, modify, list, and maintain
object library, help library, text library, and assembler macro library files.
library file
A direct access file containing one or more modules of the same module type.
library procedure
A procedure explicitly called using the equivalent of a call statement or function
reference. Such procedures are usually language independent.
LIFO
Last-in/first-out; the order in which processing is performed. For example, a
LIFO queue would process data on a last-come, first-served basis. See FIFO.
limit
The size or number of given items requiring system resources (such as mailboxes,
locked pages, I/O requests, open files, and so on) that a job is allowed to have at
any one time during execution, as specified by the system manager in the user
authorization file. See quota.

Glossary–52

line
The network management component that provides a distinct physical data path.
line buffer
A storage area used to store the last line deleted by an EDT delete line operation.
line feed
The ASCII command character that moves the cursor position down one line.
line number
A number used to identify a line of text in a file processed by a text editor.
line printer
An output device that prints files one line at a time. It is used for printing large
amounts of output that would otherwise tie up a slower device. Almost every
system has a device designated as the line printer. In some cases, the ‘‘line
printer’’ is actually a high-speed terminal.
link access protocol (LAP)
A set of procedures used for link control on a packet switching data network.
X.25 defines two sets of procedures:
•

LAP—The data terminal equipment/data circuit-terminating equipment
(DTE/DCE) interface is defined as operating in two-way simultaneous
asynchronous response mode (ARM) with the DTE and DCE containing a
primary and secondary function.

•

LAPB—The DTE/DCE interface is defined as operating in two-way
asynchronous balanced mode (ABM).

linker
A system program that creates an executable program, called an image, from one
or more object modules produced by a language compiler or assembler. Programs
must be linked before they can be executed.
linking
The resolution of external references between the object modules used to create
an image; the acquisition of referenced library routines, service entry points, and
data for the image; and the assignment of virtual addresses to components of an
image.
LMB
See logical memory block.
load assist agent
An image that provides additional data required to perform a downline system
load to a node in a local area VMScluster configuration.
load balancing
A function of the operating system by which work is distributed equally among
all processors in a system. For more information, see static load balancing and
dynamic load balancing.

Glossary–53

load device
The drive that holds the distribution media during software installation.
load/store architecture
A machine architecture in which data items are first loaded into a processor
register, then operated on, and finally stored back to memory. No operations on
memory other than load and store are provided by the instruction set.
local area transport, LAT
A communications protocol that the operating system uses within a local area
network to communicate with terminal servers.
local area VAXcluster system
A type of VAXcluster configuration in which cluster communication is carried out
over the Ethernet by software that emulates certain computer interconnect, or
CI, port functions. A VAXcluster node can be a VAX or a MicroVAX processor;
hierarchical storage controllers, or HSCs, are not used.
local disk
A disk drive in a computer interconnect, or CI, environment that is independent
of the hierarchical storage controller, or HSC.
local drive
Any drive that is connected directly to a computer.
locality
See program locality.
local node
The network node at which the user is physically located.
local symbol
(1) A symbol meaningful only to the module that defines it. Symbols not
identified to a language processor as global symbols are considered to be local
symbols. A language processor resolves (matches references with definitions)
local symbols. They are not known to the linker and cannot be made available to
another object module. They can, however, be passed through the linker to the
symbolic debugger. See global symbol.
(2) A command language symbol name that is accessible only at the current
command level and subsequently invoked levels. It is deleted when the command
level at which it is defined exits.
locate mode
A OpenVMS Record Management Services (RMS) record access technique in
which a program accesses records in a OpenVMS RMS I/O buffer area to reduce
overhead. See move mode.
lock
An association between a job and a resource maintained by the OpenVMS Lock
Manager. A lock is normally used to synchronize access by multiple processes to
shared objects.

Glossary–54

locked password
A password that cannot be changed by the account’s owner. Only system
managers or users with the SYSPRV privilege can change locked passwords.
locking a page in memory
Making a page in a process ineligible for either paging or swapping. A page stays
locked in physical memory until the operating system specifically unlocks it.
locking a page in the working set
Making a page within a process ineligible for paging out of the working set for
the process. The page can be swapped when the process is swapped. A page
stays locked in a working set until it is specifically unlocked.
lock manager
A facility that mediates lock requests.
lock mode
A value associated with a request to the lock management system services,
indicating the compatibility of the requested lock with other locks.
lock status block
Location containing the lock identification, final completion status, and optionally,
a lock value block.
lock step
When two or more CPUs execute exactly the same operations at exactly the same
time.
lock value block
An optional block of data associated with a lock-status block. The lock value block
can be used to communicate information among processes sharing a resource.
log
A record of performance or system-relevant events.
logging
The network management component that routes event data to logging sinks
such as a console or file.
logging file
The destination to which a machine-readable record of events is sent for later
retrieval. The logging file is user defined.
logging in
The identification of a user to the system. When users log in, they type a user
name and password in response to prompts from the system. If the user name
and the password match an account on the system, the user is allowed access to
the system.

Glossary–55

logging console
The destination to which a record of events is sent in a form that is
comprehensible to system users. Typically, a logging console is a terminal or a
user-specified file.
logging monitor
The destination to which a machine-readable record of events is sent for possible
real-time decision making. Typically, the logging monitor is a user-defined
program.
logging out
Entering the DIGITAL Command Language (DCL) command LOGOUT, which
informs the operating system that the user has finished using a particular
terminal.
logical block number (LBN)
A volume-relative address of a block on a mass storage device. The blocks that
form the volume are labeled sequentially starting with logical block 0. Volume
shadowing duplicates data by writing it to identical logical blocks on multiple
disks. See physical block number and virtual block number.
logical channel
A logical link between data terminal equipment (DTE) and its data circuitterminating equipment (DCE). The physical communications line between a DTE
and DCE is divided into a set of logical channels.
logical channel number (LCN)
A unique reference number that identifies a logical channel. Data terminal
equipment (DTE) recognizes a virtual circuit by its associated LCN.
logical device name
Equate a somewhat cryptic device name to a short, meaningful name.
logical expression
An expression that has a true or false value.
logical I/O access
Right to perform a set of I/O operations that allow restricted direct access to
device level I/O operations using logical block addresses.
logical I/O function
A set of I/O operations (for example, read and write logical block) that allow
restricted direct access to device level I/O operations using logical block addresses.
logical link
(1) A communication path between programs on two network nodes. See physical
link.
(2) A carrier of a single stream of full-duplex traffic between two user-level
processes.

Glossary–56

logical memory block (LMB)
The portion of information written to the dump file during a selective crash
dump. Each LMB includes a header block describing the data structure, blocks
describing the parts of the address space that could not be dumped, and the
dumpable parts of virtual address space.
LMBs exist for system and global page tables, system space, global pages in use
by a process or processes, and for individual processes.
logical name
A user-specified name for any portion or all of a file specification. For example,
the logical name INPUT can be assigned to a terminal device from which a
program reads data entered by a user. Logical name assignments are maintained
in logical name tables for each process, each group, and the system. Logical
names can be assigned translation attributes, such as terminal and concealed.
See search list.
logical name table
A table that contains a set of logical names and their equivalence names for a
particular process, a particular group, or the system.
logical record
A group of related fields treated as a unit.
login command procedure
A command procedure that is automatically executed at login and at the
beginning of a batch job
login directory
The default directory established by LOGINOUT when a when a user logs in.
login file
A command procedure that is automatically executed at login and at the
beginning of a batch job.
log manager
Software that provides a mechanism for storing a permanent record of transaction
states in log files. A log file is a sequence of transaction records.
longword
Four contiguous bytes (32 bits) starting on any addressable byte boundary. Bits
are numbered from right to left, 0 to 31. The address of the longword is the
address of the byte containing the low-order bit (bit 0). A longword is naturally
aligned if its address is evenly divisible by 4.
loop node
A local node associated with a particular line and treated as if it were a remote
node. All traffic to the loop node is sent over the associated line.
loosely coupled system
A multiprocessing system configuration consisting of separate operating systems
that communicate through some message transfer mechanism. See tightly
coupled system.

Glossary–57

macro
A statement that requests a language processor to generate a predefined set of
instructions.
magnetic tape
Medium on which data can be stored and accessed.
magnetic tape ancillary control process (MTACP)
The internal software process of the operating system that interprets the logical
format of ANSI-labeled volumes.
mailbox
A software data structure that is treated as a record-oriented device for general
interprocess communication. Communication using a mailbox is similar to other
forms of device-independent I/O. Senders write to a mailbox, the receiver reads
from that mailbox. Some systemwide mailboxes are defined; the error logger and
operator communication manager (OPCOM) read from systemwide mailboxes.
main memory
See physical memory.
main text buffer
In a text editor, the default text buffer for keyboard input and for input files, and
the source for output files.
manual record unlocking
A OpenVMS Record Management Services (RMS) capability that allows users to
lock multiple records in a file simultaneously. The user has explicit control over
the unlocking of records. A lock occurs when the RAB$V_ULK bit is set in the
record processing options field on the execution of a Get, Find, or Put service.
Once a record is locked when record unlocking is enabled, it will remain locked
until it is explicitly unlocked by either the Free or Release service, or until the
stream terminates.
mapping window
A subset of file retrieval information used to translate virtual block numbers to
logical block numbers.
marginal vector consumer
A process executing an image that has issued VAX vector instructions, but
has not issued any instructions in the amount of time determined by the
VECTOR_MARGIN system parameter. A marginal vector consumer relinquishes
its need for the VECTOR capability and, thus, need no longer be scheduled on an
available scalar-vector processor pair. A marginal vector consumer is eligible for
execution on any processor in the system. See vector consumer.
MASSBUS adapter (MBA)
An interface device between the backplane interconnect and the MASSBUS
device.
mass storage control protocol, MSCP
The software protocol used to communicate I/O commands between a VAX
processor and DSA-compliant devices on the system.
Glossary–58

mass storage device
An input/output device on which data and other types of files are stored while
they are not being used. Typical mass-storage devices include disks, magnetic
tapes, and floppy disks.
master file directory (MFD)
The file directory on a disk volume that contains the name of all user file
directories (UFDs) on a disk, including its own.
maximum visits
The maximum number of nodes through which a packet can be routed before
reaching its destination.
MBA
See MASSBUS adapter.
MBZ
See must be zero.
MCR
See monitor console routine.
mean-time-between-failures (MTBF)
The average time that passes before a computing component fails such that
remedial action is required.
member number
The second number or its alphanumeric equivalent in a user identification code
(UIC) that uniquely identifies that code.
member unit
See shadow set member.
memory
A series of physical locations into which data or instructions can be placed in the
form of binary words. Each location in memory can be addressed and its contents
can be altered. Memory should not be confused with mass-storage devices.
memory management
The operating system functions that include the hardware’s page mapping and
protection and the operating system’s image activator and pager.
merge member
A shadow set member that is partially consistent with all other merge members
of the shadow set. Only partial inconsistencies exist among the merge members
so that some number of blocks were written and some were not at the time of a
hardware failure.

Glossary–59

merge operation
An operation that brings shadow set members, which are in a partially consistent
state, into a fully consistent state while also permitting I/O operations to occur
on the shadow set. A merge operation also attempts to correct blocks that are
inconsistent on disk devices that were once members of the same shadow set. For
a merge operation to occur, the shadowing software recognizes that the shadow
set members are all former members of the same shadow set and the data on one
member is just as correct as the data on any other member.
MFD
See master file directory.
Mixed Interconnect VMScluster System
Any VMScluster system that utilizes more than one interconnect (CI, DSSI,
Ethernet, LAN) for SCA traffic. Mixed interconnect VMScluster systems provide
maximum flexibility in combining CPUs, storage, and workstations into highly
available configurations.
minimerge assist
Provides more efficient volume shadowing merge operation processing by logging
information about write operations in the controller’s memory. These write logs
are used to locate exactly the LBNs in the shadow set that had write I/O requests
outstanding when a node failed. The remaining nodes merge those LBNs that are
inconsistent across the shadow set.
modem
Contraction of modulator/demodulator. A device that modulates signals for
sending over communications facilities and demodulates signals being received.
modify access type
A type of access in which the specified operand of a VAX instruction or procedure
is read and potentially modified and written during execution.
module
(1) A portion of a program or program library, as in a source module, object
module, or image module.
(2) A board, usually made of plastic covered with an electrical conductor, on which
logic devices (such as transistors, resistors, and memory chips) are mounted, and
circuits connecting these devices are etched, as in a logic module.
(3) A network management component.
monitor console routine (MCR)
The command interpreter in an RSX–11 system; also an optional command
interpreter in the operating system.
mounting a volume
(1) Logically associating a volume with the physical unit on which it is loaded (an
activity accomplished by system software at the request of an operator).
(2) Loading or placing a magnetic tape or disk pack on a drive and placing the
drive on line (an activity accomplished by a system operator).

Glossary–60

mount verification
A feature that suspends I/O to and from volumes while they are changing
status. Mount verification also ensures that, following a suspension in disk
I/O, the volume being accessed is the same as was previously mounted. When
volume shadowing is installed, the mount verification feature also maintains and
validates shadow set membership for Files–11 shadow sets.
move mode
A OpenVMS Record Management Services (RMS) record I/O access technique in
which a program accesses records in its own working storage area. See locate
mode.
MSCP
See mass storage control protocol.
MTACP
See magnetic tape ancillary control process.
MTBF
See mean-time-between-failures.
multiaccess channel
A media (for example, Ethernet) on which many transmitters contend for access.
multicast addressing
An Ethernet addressing mode in which a given message packet is targeted to a
group of logically related nodes.
multicast group address
An address assigned to a number of nodes on an Ethernet and used to send a
message to all nodes in the group in a single transmission.
multinational character set
A set of 8-bit character international alphanumeric characters, including
characters with diacritical marks.
multipoint circuit
A circuit connecting two systems, with one of the systems (the control station)
controlling the circuit and the other system serving as a tributary.
multiport memory
A memory unit that can be connected to multiple VAX processors and that can
contain resources (for example, mailboxes, common event flag clusters, and global
sections) for use by processes running on different processors.
multiprocessing system
A system containing two or more general-purpose processors. These processors
are connected, through hardware, so that they can work on the same application
concurrently. See asymmetric multiprocessing and symmetric multiprocessing.

Glossary–61

multiprogramming
A mode of operation in which hardware resources are shared among multiple,
independent software processes.
must be zero (MBZ)
A field that is reserved and must be supplied as zero. If examined, it must be
assumed to be undefined.
mutex
A semaphore used to control exclusive access to a region of code that can share
a data structure or other resource. The mutex (mutual exclusion) semaphore
ensures that only one process at a time has write access to the region of code.
NAM
See name block.
name block (NAM)
A OpenVMS Record Management Services (RMS) user data structure that
contains supplementary information used in parsing file specifications.
National Replacement Character (NRC)
A 7-bit character set that is a country-specific version of ASCII.
native image
An image whose instructions are executed in native mode.
natural alignment
Data storage in memory such that the address of the data is evenly divisible by
the size of the data in bytes. For example, a naturally aligned longword has an
address that is evenly divisible by 4, and a naturally aligned quadword has an
address that is evenly divisible by 8. A structure is naturally aligned when all its
members are naturally aligned.
NCP
See Network Control Program.
NETACP
See network ancillary control process.
NETPROXY
See network proxy authorization file.
network
A collection of interconnected individual computer systems.
network ancillary control process (NETACP)
An ancillary control process that controls all lines and circuits, maintains a
picture of the network topology, and creates a process to receive inbound logical
link requests.

Glossary–62

network connect block (NCB)
(1) For a DECnet for OpenVMS network, a user-generated data structure used in
a nontransparent task to identify a remote task and optionally send user data in
calls to request, accept, or reject a logical link connection.
(2) For the VAX Packetnet System Interface (PSI), a block that contains the
information necessary to set up an X.25 virtual circuit or to accept or reject a
request to set up an X.25 virtual circuit.
Network Control Program (NCP)
An interactive utility program that permits you to control and monitor the
network.
network object
Any task with a nonzero object type, for example, those programs such as FAL
and NML that provide generic services across a network.
network proxy authorization file (NETPROXY)
A file (NETPROXY.DAT) containing an entry for each user authorized to connect
to the local system from a remote node in the network. It is sometimes referred
to as the network user authorization file (NETUAF.DAT).
network services protocol (NSP)
A formal set of conventions used in a DECnet for OpenVMS network to perform
network management and to exchange messages over logical links.
network status notification
Information about the state of both logical and physical links over which two
tasks communicate. A nontransparent task can use this information to take
appropriate action under conditions such as third-party disconnections and a
partner’s exiting before I/O completion.
network task
A nontransparent task that is able to process multiple inbound connection
requests; that is, it has declared a network name or object number.
node
(1) An individual computer system in a network that can communicate with other
computer systems in the network.
(2) A VAXBI interface—such as a central processor, controller, or memory
subsystem—that occupies one of 16 logical locations on a VAXBI bus. See VAXBI.
(3) A VAX processor or HSC that is recognized by system communications services
(SCS) software.
node address
The required, unique, numeric identification of a specific node in the network.
node name
An optional alphanumeric identification associated with a node address in a strict
one-to-one mapping. A node name must contain at least one alphabetic character.

Glossary–63

node specification
The first field in a file specification. This field identifies the location of a computer
system in a network.
noncommand image
A program not associated with a DCL command. To invoke a noncommand
image, use the file name containing the program as the parameter to the RUN
command.
nonprinting character
A character in the computer code set for which there is no corresponding graphic
symbol.
nonprivileged
(1) An account with no privilege other than TMPMBX and NETMBX and a user
identification code (UIC) greater than the system parameter MAXSYSGROUP.
(2) In DECnet for OpenVMS, this term means no privileges in addition to
NETMBX, which is the minimal requirement for any network activity.
nonrouting node
See end node.
NRC
See National Replacement Character.
NSP
See network services protocol.
null
(1) The character with the ASCII code 000.
(2) An absence of information.
null string
A string without content or an empty string represented by adjacent quotation
marks.
null value
A string with no characters that is represented in a command procedure by
double quotation marks ( "" ).
numeric expression
A mathematical statement consisting of a collection of operands connected by
arithmetic operators.
numeric string
A contiguous sequence of bytes representing up to 31 decimal digits (one per
byte) and possibly a sign. The numeric string is specified by its lowest addressed
location, its length, and its sign representation.

Glossary–64

object
(1) A passive repository of information to which the system controls access.
Access to an object implies access to the information it contains. Examples of
protected objects are files, volumes, global sections, and devices.
(2) A DECnet for OpenVMS process that receives a logical link request.
It performs a specific network function or is a user-defined image for a
special-purpose application.
(3) A VAX Packetnet System Interface (PSI) management component that
contains records to specify account information for incoming calls and to specify a
command procedure that is initiated when the incoming call arrives.
object class
On VAX systems, a set of protected objects with common characteristics. For
example, all files belong to the FILE class whereas all devices belong to the
DEVICE class.
object module
The binary output of a language processor such as the assembler or a compiler,
which is used as input to the linker.
object program
A source program that has been translated into machine language.
object time system
See Run-Time Procedure Library.
object type
A discrete identifier for either a task or DECnet for OpenVMS service on a
remote node. Object type identifiers can either be 0 plus a name (alternatively,
TASK=name) or nonzero without a name (for example, 17= or FAL=).
octal number
A number in the base-8 numbering system. Only the numerals 0 through 7 are
used in this system. If a number includes an 8 or a 9, it cannot be an octal
number. Octal numbering is used in computer systems because it is easy to
convert to the binary numbers that are actually used by the computer.
octaword
Eight contiguous words (128 bits) starting on any addressable byte boundary.
Bits are numbered from right to left, 0 to 127. The address of an octaword is the
address of the word containing the low-order bit (bit 0). An octaword is naturally
aligned if its address is evenly divisible by 16.
offset
A fixed displacement from the beginning of a data structure. System offsets for
items within a data structure normally have an associated symbolic name used
instead of the numeric displacement. Where symbols are defined, programmers
always reference the symbolic names for items in a data structure instead of
using the numeric displacement.
OLTP
See Online Transaction Processing.
Glossary–65

On-Disk Structure Level 1 (ODS1)
See Files–11 On-Disk Structure Level 1.
On-Disk Structure Level 2 (ODS2)
See Files–11 On-Disk Structure Level 2.
Online Transaction Processing (OLTP)
An environment in which many users are simultaneously reading and writing to
a collection of shared data, generally a database. Results are usually expected
immediately (real time). In contrast to standard transaction processing, when an
OLTP transaction is completed, all data is fully updated during the request and
output stages. No files are created for later batch updates of the stored data. See
transaction processing.
opcode
The pattern of bits within an instruction that specifies the operation to be
performed.
OPCOM
See operator communication manager.
open
To prepare a data set or file for processing.
open account
An account that does not require a password.
operand
The part of an expression that contains a value. Operands are acted on by
operators during expression evaluation to produce a result.
operating system
An integrated collection of programs that controls the execution of computer
programs and performs system functions.
operator
(1) The person responsible for daily maintenance of the system at a particular
installation. The operator does such things as mounting disks and tapes,
changing ribbons and paper on line printers, rebooting the system, keeping
records, and so forth. In small systems, these duties may be combined with those
of the system manager or informally divided among several people.
(2) The part of an expression that tells the computer how to manipulate the
operands. For example, the plus sign (+) is an operator that tells the computer to
perform addition.
operator communication manager (OPCOM)
A system process that receives input from a process that wants to inform an
operator of a particular status or condition, passes a message to the operator, and
tracks the message.
operator console
Any terminal identified as a terminal attended by a system operator.
Glossary–66

operator terminal
A terminal attended by a system operator. The system can send system event
messages to the terminal, provided the event class is enabled.
out-of-order packet caching
The mechanism by which the network services protocol (NSP) maintains a buffer
of data packets received out of order so that they can be reassembled in the
correct order before being forwarded to the destination node.
outbound connection
A task’s request for a logical link connection to another node.
output file
A file that contains the results of a processing operation, for example, a file that
has been sorted or edited.
owner
A user with the same user identification code (UIC) as the protected object.
An owner always has control access to the object and can therefore modify the
object’s security profile. When the system processes an access request from an
owner, it considers the access rights in the owner field of a protection code.
owner process
The process or subprocess that created a subprocess.
P0
See program region.
P1
See control region.
P1 through P8
See parameter.
P1BR
See control region base register.
P1LR
See control region length register.
P1PT
See control region page table.
packed decimal
A method of representing a decimal number by storing a pair of decimal digits in
1 byte, taking advantage of the fact that only four bits are required to represent
the numbers 0 through 9.

Glossary–67

packed decimal string
A contiguous sequence of up to 16 bytes interpreted as a string of 4-bit fields.
Each field represents a digit except for the low-order four bits of the highest
addressed byte, which represent the sign. The packed decimal string is specified
by its lowest addressed location and by the number of digits.
packet
A unit of data to be routed from a source node to a destination node; for the VAX
Packetnet System Interface (PSI), the unit of data switched through a packet
switching data network (PSDN). Normally, a user data field accompanied by a
header carrying destination and other information.
packet assembly/disassembly (PAD) facility
A device at a packet switching data network (PSDN) that allows access from an
asynchronous terminal. The terminal connects to the PAD, and the PAD puts the
terminal’s input data into packets (assembles) and takes the terminal’s output
data out of packets (disassembles).
Packetnet System Interface (PSI)
A software product that allows the user to communicate across packet switching
data networks (PSDNs).
packet switching
A data transmission process, utilizing addressed packets, whereby a channel is
occupied only for the duration of transmission of the packet.
PAD
See packet assembly/disassembly (PAD) facility.
packet switching data network (PSDN)
A set of equipment and interconnecting links that provides a packet switching
communications service to subscribers.
page
(1) set of contiguous byte locations used as the unit of memory mapping and
protection. An AXP memory page can be 8KB, 16KB, 32KB, or 64KB depending
upon system implementation. A VAX memory page is always 512 bytes. On
either system, a page is aligned on a boundary that is an even multiple of its size.
(2) The data between the beginning of file and a page marker, between two
markers, or between a marker and the end of a file. See pagelet.
page fault
An exception generated by a reference to a page that is not in the working set of
the faulting process. See translation-not-valid fault.
page fault cluster
See cluster.
page fault cluster size
The number of pages read into memory on a page fault.

Glossary–68

page frame number (PFN)
The high-order bits of the physical address of a page in physical memory.
page frame number mapping (PFN mapping)
Mapping a section to one or more pages in physical memory or I/O space (as
opposed to mapping it to a disk file).
pagelet
A 512-byte unit of memory in an AXP environment. On AXP systems, certain
DCL and utility commands, system services, and system routines accept as input
or provide as output memory requirements and quotas in terms of pagelets.
Although this allows the external interfaces of these components to be compatible
with those of VAX systems, AXP systems internally manage memory only in even
multiples of the CPU memory page size. See page.
page marker
A character or characters (generally a form feed) that separates pages in a file
processed by a text editor.
pager
A set of kernel mode procedures that executes as the result of a page fault. The
pager makes the page for which the fault occurred available in physical memory
so that the image can continue execution. The pager and the image activator
provide the operating system’s memory management functions.
page size
The number of bytes that a system’s hardware treats as a unit for address
mapping, sharing, protection, and movement to and from secondary storage.
page table
A memory management data base used to account for virtual pages. See system
page table, process page table, and global page table.
page table base register (PTBR)
On AXP systems, the processor register or its equivalent, in a hardware
privileged context block that contains the page frame number of the process’s first
level page table.
page table entry (PTE)
The data structure that identifies the physical location and status of a page of
virtual address space. When a virtual page is in memory, the PTE contains the
page frame number needed to map the virtual page to a physical page. When it
is not in memory, the page table entry contains the information needed to locate
the page on secondary storage (disk).
paging
The action of bringing pages of an executing process into physical memory
when referenced. When a process executes, all of its pages are said to reside
in virtual memory. Only the actively used pages, however, need to reside in
physical memory. The remaining pages can reside on disk until they are needed
in physical memory. A process is paged either when it references more pages
than it is allowed to have in its working set or when it first activates an image
in memory. When the process refers to a page not in its working set, a page
Glossary–69

fault occurs. This faulting causes the operating system’s pager to read in the
referenced page if it is on disk (and, optionally, other related pages depending
on a cluster factor), replacing the least recently faulted pages as needed. The
operating system’s pager does not read in a referenced page if that page is on the
free or modified list.
parallel processing
A method of computing that occurs when a section of an application is divided
into multiple tasks, and those multiple tasks are executed simultaneously on
multiple processors.
parameter
(1) A value passed to a command procedure equated to a symbol ranging from P1
through P8. See command parameter.
(2) An entry in the volatile or permanent database for a network management
component.
parsing
(1) Breaking a command string into its elements to interpret it.
(2) Interpreting a file specification, as is done by OpenVMS Record Management
Services (RMS).
password
A character string that users provide at login time to validate their identity and
as a form of proof of their authorization to access the account. There are two
kinds of passwords—system passwords and user passwords. User passwords
include both primary and secondary passwords.
path
The route a packet takes from source to destination.
path cost
The sum of the circuit costs along a path between two nodes.
path length
The number of hops along a path between two nodes; that is, the number of
circuits a packet must travel along to reach its destination.
PC
See program counter.
PCB
See process control block.
performance assist
OpenVMS Volume Shadowing uses controller performance assists to improve
full copy and merge operation performance. There are two distinct types of
performance assists: the full copy assist and the minimerge assist.

Glossary–70

peripheral device
Any unit, distinct from the CPU and physical memory, that can provide the
system with input or accept any output. Terminals, line printers, and disks are
peripheral devices.
permanent database
A file containing information about network management components. See
volatile database and configuration database.
permanent virtual circuit (PVC)
A permanent logical association between two DTEs (data terminal equipment),
which is analogous to a leased line. Packets are routed directly by the network
from one DTE to the other.
per-process address space
See process address space.
PFN
See page frame number.
PFN mapping
See page frame number mapping.
PHD
See process header.
physical address
(1) The address used by hardware to identify a location in physical memory or on
directly addressable secondary storage devices such as disk. A physical memory
address consists of a page frame number and the number of a byte within the
page. A physical disk block address consists of a cylinder or track and sector
number.
(2) The unique address value associated with a given system on an Ethernet
circuit. An Ethernet physical address is defined to be distinct from all other
physical addresses on an Ethernet circuit.
physical address space
The set of all possible physical addresses that can be used to refer to locations in
memory (memory space) or device registers (I/O space).
physical block number
The physical address of a block on a mass storage device. See logical block
number and virtual block number.
physical device name
Uniquely identifies a physical device (such as a storage disk or a terminal) to the
system.
physical I/O access
Right to perform a set of I/O functions that allows access to all device-level I/O
operations except maintenance mode using physical block addresses.

Glossary–71

physical link
A signal-carrying media that links two nodes in a network. See logical link.
physical memory
The memory modules connected to the backplane interconnect that are used to
store both instructions that the processor can directly fetch and execute and any
other data that a processor is instructed to manipulate. Also called main memory.
PID
See process identification.
point-to-point circuit
A circuit that connects two nodes, operating over a single line.
polling
The activity that the control station performs with a multipoint circuit’s
tributaries to grant the tributaries permission to transmit.
position-dependent code
Code that can execute properly only in the locations in virtual address space that
are assigned to it by the linker.
position-independent code
Code that can execute properly without modification wherever it is located in
virtual address space, even if its location is changed after it is linked. Generally,
this code uses addressing modes that form an effective address relative to the
program counter (PC).
primary key
The mandatory key within the data records of an indexed file; used by OpenVMS
Record Management Services (RMS) to determine the placement of records within
the file and to build the primary index. See key (indexed files) and alternate key.
primary password
A type of user password that is the first password requested from the user.
Systems may optionally require a secondary password, as well. As a user
password, this password must be associated with the user name that is supplied
with it.
primary processor
The processor in a symmetric multiprocessing system that is either logically or
physically attached to the console device. Only the primary processor performs
the initialization activities that define the environment and prepare memory
for the entire system. In addition, the primary processor serves as the system
timekeeper. See secondary processor.
primary vector
A location that contains the starting address of a condition handler to be
executed when an exception condition occurs. If a primary vector is declared, that
condition handler is the first handler to be executed.

Glossary–72

print queue
A list of files waiting to be printed.
priority
See process priority and interrupt priority level.
private section
An image section of a process that is not shareable among processes. See global
section.
private volume
A volume that has been allocated by a process for its own exclusive use.
privilege
A means of protecting the use of certain system functions that can affect system
resources and integrity. System managers grant privileges according to user’s
needs and deny them to users as a means of restricting their access to the
system. See process privileges, user privileges, and image privileges.
privileged
Generally refers to instructions, images, or accounts intended for use by the
operating system, specific system programs, or a subset of the system users.
procedure
A closed sequence of instructions (routine) entered by means of a call instruction
and then returns control to the calling program. See command procedure.
procedure value
An address value that represents a procedure. In the VAX environment, a
procedure value is the address of the entry mask that is interpreted by the
CALLx instruction invoking the procedure. In an AXP environment, a procedure
value is the address of the procedure descriptor for the procedure.
procedure value register
On AXP systems, integer register 27 (R27). In a standard call, the procedure
value of the procedure being called is passed in this register.
process
The basic entity scheduled by the system software, a process provides the context
in which an image executes. A process consists of an address space and both
hardware and software context.
process address space
See process space.
process affinity
In a symmetric multiprocessing system, a close association of a process with
a specific processor or set of processors in the system. Process affinity can be
indicated as either a requirement that a process run only on the processor with
a specific CPU identification or on a processor or set of processors that have a
needed capability. See capability.

Glossary–73

process context
The set of data defining the environment, both hardware and software, in which
a process executes. See hardware context and software context.
process control block (PCB)
A data structure used to contain process context. The hardware PCB contains
the hardware context. The software PCB contains the software context, which
includes a pointer to the hardware PCB.
process header (PHD)
A data structure that contains the hardware process control block (PCB),
accounting and quota information, process section table, working set list, and the
page tables defining the virtual layout of the process.
process header slots
That portion of the system address space in which the system stores the process
headers for the processes in the balance set. The number of process header slots
in the system determines the number of processes that can be in the balance set
at any one time.
process identification (PID)
A 32-bit binary value that uniquely identifies a process. Each process has a
process identification and a process name.
process I/O channel
See channel.
process I/O segment
That portion of a process control region that contains the process permanent
OpenVMS Record Management Services (RMS) internal file access block for each
open file, and the I/O buffers, including the command interpreter’s command
buffer and command descriptors.
process name
A 1- to 15-character ASCII string that can be used to identify processes executing
under the same group number.
processor-memory interconnect
On AXP systems, an interconnect on which the CPU and memory communicate.
I/O widgets and I/O adapters can also connect to the PMI.
processor register
A part of the processor used by the operating system software to control the
execution states of the computer system. Processor registers on VAX systems
include, for example, the system base and length registers, the program and
control region base and length registers, the system control block base register,
and the software interrupt request register. On AXP systems, processor registers
include the page table base register, software interrupt request register, and
privileged context base register.

Glossary–74

processor status (PSL)
On VAX systems, a privileged processor register, known as the processor
status longword (PSL), consisting of a word of privileged processor status and
the processor status word itself. The privileged processor status information
includes the current interrupt priority level (IPL), the previous access mode, the
current access mode, the interrupt stack bit, the trace trap pending bit, and the
compatibility mode bit.
On AXP systems, a privileged processor register known as the processor status
(PS). It consists of a quadword of information including the current access mode,
the current IPL, the stack alignment, and several reserved fields.
processor status word (PSW)
On VAX systems, the low-order word of the processor status longword. Processor
status information includes the condition codes (carry, overflow, 0, negative),
the arithmetic trap enable bits (integer overflow, decimal overflow, floating
underflow), and the trace enable bit.
process page tables
The page tables used to describe process virtual memory.
process permanent file
A file that is opened or created through OpenVMS Record Management Services
(RMS) by supervisor or executive mode when the process permanent bit is set in
the file-processing options field.
process priority
The priority assigned to a process for scheduling purposes. The operating system
recognizes 32 levels of process priority, where 0 is low and 31 high. Levels 16
through 31 are used for real-time processes. The system does not modify the
priority of a real-time process (although the system manager or the process
itself may). Levels 0 through 15 are used for normal processes. The system may
temporarily increase the priority of a normal process based on the activity of the
process.
process privileges
The privileges granted to a process by the system. These privileges are a
combination of user privileges and image privileges. They include, for example,
the privilege to affect other processes associated with the same group as the
user’s group, to affect any process in the system regardless of user identification
code (UIC), to set process swap mode, to create permanent event flag clusters,
to create another process, to create a mailbox, to perform direct I/O to a
file-structured device, and to perform network operations.
process section
See private section.
process space
The lowest addressed half of virtual address space, where process instructions
and data reside. Process space is divided into a program region and a control
region.

Glossary–75

program
A series of instructions aimed at a particular result. Programming languages are
a means of describing procedures so that they can be performed by a computer.
See image.
program counter (PC)
A CPU register that contains the virtual address of the next instruction to be
executed. The register is incremented as each instruction is executed. On VAX
systems, R15 serves as the PC. On AXP systems, the PC is a special processor
register.
program locality
A characteristic of a program that indicates how close or far apart the references
to locations in virtual memory are over time. A program with a high degree
of locality does not refer to many widely scattered virtual addresses in a short
period of time.
programmer number
See member number.
program region (P0)
The lowest addressed half of process address space (P0 region). The program
region contains the image currently being executed by the process and other user
code called by the image.
program section (PSECT)
A portion of a program with a given protection and set of storage management
attributes. Program sections that have the same attributes are gathered together
by the linker to form an image section.
project number
See group number.
prompt
A character string appearing on a terminal indicating that the user must provide
input.
protected subsystem
An application with enhanced access control. While users run the application,
their process rights list contains identifiers giving them access to objects owned
by the subsystem. As soon as they exit the application, these identifiers and,
therefore, access rights to objects are taken away.
protection
The attributes of an object that limit the type of access available to users. See
user identification code (UIC), protection code, and access control list.
protection code
A code defining the type of access that users are allowed to objects, based on the
user’s relationship to the object’s owner. The code defines four sets of users: those
with system rights, those with ownership rights, those belonging to the same
group, and all users on the system, who are called world users.

Glossary–76

protocol
An agreed set of rules governing the operation of a communications link.
proxy login
The procedure that permits a remote user to access a specific account at the local
node, without supplying the user name and password.
PSDN
See packet switching data network.
PSECT
See program section.
pseudodevice
An entity similar to a mailbox that is treated as an I/O device by the user or
system, although it is not any particular physical device.
PSI
See Packetnet System Interface.
PSL
See processor status.
PSW
See processor status word.
PTBR
See page table base register.
PTE
See page table entry.
public volume
A file-structured disk volume that contains public files.
pure code
See reentrant code.
PVC
See permanent virtual circuit.
QIO
See Queue I/O Request system service.
quadword
Four contiguous words (64 bits) starting on any addressable byte boundary.
Bits are numbered from right to left, 0 to 63. The address of a quadword is the
address of the word containing the low-order bit (bit 0). A quadword is naturally
aligned if its address is evenly divisible by 8.

Glossary–77

qualifier
A portion of a command string that modifies a command verb or command
parameter by selecting one of several options. A qualifier, if present, follows
the command verb or parameter to which it applies and is in the format
/qualifier[=option]. For example, in the command string ‘‘PRINT filename
/COPIES=3,’’ the COPIES qualifier indicates that the user wants three copies of a
given file printed.
quantum
The minimum amount of time that a process can remain in memory; also the
maximum amount of time that a process can be the executing process. A specified
amount is deducted from the quantum whenever a process enters a wait state.
queue
(1) A line of jobs to be processed, for example, a batch job queue or a printer job
queue. Processing occurs primarily in first-in/first-out (FIFO) order, but does
reflect the priority of the process that submitted the job. See state queue and
system queue.
(2) To make an entry in a list or table, perhaps using the INSQUE instruction.
Queue I/O Request system service (QIO)
The system service that handles $QIO and $QIOW requests. The QIO prepares
an I/O request for processing by the driver and performs device-independent
preprocessing of the request. This system service also calls driver function
decision table (FDT) routines.
queue priority
The priority assigned to a job placed in a spooler queue or a batch queue.
quota
The total amount of a system resource, such as CPU time, that a job is allowed
to use in an accounting period, as specified by the system manager in the user
authorization file. See limit.
RA
See record address register.
RAB
See record access block.
random access
A method for retrieving or writing data in which the location of the data to be
retrieved or written is not dependent on the location of previously retrieved or
written data. Random access refers to memory or mass-storage devices on which
all information is equally accessible.
random access by key
The retrieval or storage of a record by specifying the key value. This method of
record retrieval and storage applies only to indexed files.

Glossary–78

random access by record file address (RFA)
The retrieval of a record by its unique address, which is provided to the program
by OpenVMS Record Management Services (RMS) upon successful $GET
or $FIND operations. The record’s file address can subsequently be used to
randomly access that same record.
random access by relative record number
The retrieval or storage of a record by specifying its position relative to the
beginning of the file. This method of record storage and retrieval applies only to
sequential files with fixed-length records and relative files.
reachable node
A node to which the local node has a usable communications path.
read
The act or capability of an image to accept data. For example, when a TYPE
command is entered, the system reads the designated file from the disk and
writes it to the terminal. See write.
read access type
An instruction or procedure operand attribute indicating that the specified
operand is only read during instruction or procedure execution.
read miss
An event in which a read operation cannot be serviced by the processor’s
hardware cache.
read-modify-write operation
A hardware operation that involves the reading, modifying, and writing of a piece
of data in main memory as a single, uninterruptible operation.
read-write ordering
The order in which memory on one CPU becomes visible to an execution agent (a
different CPU or device within a tightly-coupled system).
real-time process
A process that responds to events in related or controlled processes as they occur,
rather than when the computer is ready to respond to them. The results of the
computation can thus be used in the processing. A real-time process is assigned
to a software priority level between 16 and 31, inclusive. The scheduling priority
assigned to a real-time process is never modified by the scheduler, although it can
be modified by the system manager or by the process itself.
real-time system
A system in which inquiries and data entered on a terminal are processed based
on need and priority.
record
A set of related data that a program treats as a unit.

Glossary–79

record access block (RAB)
A OpenVMS Record Management Services (RMS) user control block allocated
at either assembly or run time to communicate with RMS. The control block
describes the records in a particular file and associates with a file access block to
form a record access stream. A RAB defines the characteristics needed to perform
record-related operations, such as update, delete, or get.
record access mode
The method used in OpenVMS Record Management Services (RMS) for retrieving
and storing records in a file. Access is by one of four methods: sequential,
random by key, random by record’s file address, and random by relative record
number.
record access mode switching
Term applied to the switching from one type of record access mode to another
while processing a file.
record blocking
The technique of grouping multiple records into a single block. On magnetic tape,
an interrecord gap (IRG) is placed after the block rather than after each record.
This technique reduces the number of I/O transfers required to read or write the
data; and, in addition (for magnetic tape), increases the amount of usable storage
area. Record blocking also applies to disk files.
record cell
A fixed-length area in a relative file that is used to contain one record.
record file address (RFA)
The unique address of a record in a file, the RFA allows previously accessed
records to be accessed randomly at a subsequent time. This access occurs
regardless of file organization.
record format
The way a record physically appears on the recording surface of the storage
media. The record format defines the method for determining record length.
record length
The size of a record in bytes.
record locking
The ability to control operations being performed on relative and indexed files
that are being simultaneously accessed by more than one program or more than
one record stream. Record locking makes certain that when a program is adding,
deleting, or modifying a record on a given stream, another program or stream is
not allowed to access the same record or record cell. See automatic record locking
and manual record unlocking.
Record Management Services (RMS)
A set of operating system procedures that is called by programs to process files
and records within files. RMS allows programs to issue GET and PUT requests
at the record level (record I/O) as well as read and write blocks (block I/O). RMS
is an integral part of the system software; its procedures run in executive mode.

Glossary–80

record-oriented device
A device such as a terminal, line printer, or card reader on which the largest unit
of data a program can access in one I/O operation is the device’s physical record.
record sorting
A sorting process where records are kept intact and an output file consisting of
complete records is produced.
recoverability
The ability of a system to reconfigure itself and continue (or quickly resume)
operation.
Reduced Instruction Set Computer (RISC)
A computer that has an instruction set reduced in complexity, but not necessarily
in the number of instructions. RISC architectures typically require more
instructions than CISC architectures to perform a given operation, because an
individual instruction performs less work than a CISC instruction.
redundant
Duplicate or extra computing components that protect a computing system from
failure.
reentrant code
Code that is never modified during execution. It is possible to let many users
share the same copy of a procedure or program written as reentrant code.
reentrant service
A service that is safe to call from multiple threads in parallel. If a service is
reentrant, there is no burden placed on calling routines to serialize their access or
take other explicit precautions. See thread-serial service and thread-synchronous
service.
reference
A mechanism for passing parameters where the address of the parameter is
provided in the argument list by the calling program. A mechanism for passing
parameters where the address of the parameter is provided in the argument list
by the calling program.
register
A storage location in hardware logic other than main memory. See general
purpose register, processor register, integer register, floating-point register, and
device register.
relative file organization
The arrangement of records in a file in which each record occupies a cell of
equal length within a bucket. Each cell is assigned a successive number, which
represents its position relative to the beginning of the file.

Glossary–81

relative record number
An identification number used to specify the position of a record cell relative to
the beginning of the file. The relative record number is used as the key during
random access by key mode to relative files. To randomly access a record in a
sequential disk file having 512-byte, fixed-length records, a program must provide
OpenVMS Record Management Services (RMS) with the relative record number
of the cell containing the record.
relative volume number (RVN)
A volume number that uniquely identifies which volume set contains a file.
reliability
The ability of a computing system to operate without failing. Reliability is
measured by a Mean Time Between Failure (MTBF) formula.
remote data terminal equipment (DTE)
Any DTE in a network other than the one at which the user is located.
remote device
A device that is not directly connected to the local node, but is available through
the VMScluster system.
remote node
To any one node in the network, this node is any other network node. See
adjacent node, local node, and executor node.
reorganization
A record-by-record copy of an indexed file to another indexed file with the same
key attributes as the input file.
resource
(1) A physical part of the computer system such as a device or memory, or an
interlocked data structure such as a mutex. Quotas and limits control the use of
physical resources.
(2) Any entity to which access is synchronized by means of the lock management
system services.
resource manager
Software that participates in distributed transactions and manages shared access
to a recoverable resource. An example of a recoverable resource is a database
system.
resource wait mode
An execution state in which a process indicates, when it issues a service request
requiring a resource, that it will wait until a system resource becomes available.
If a process requests notification when a resource is not available, it can disable
resource wait mode during program execution.

Glossary–82

restricted account
A type of account with a secure login procedure. The user is not allowed to
use the Ctrl/Y key during the system or process login command procedure.
Control may be turned over to the user following execution of the login command
procedures.
resume
To activate a suspended process. See waking.
return address register (RA)
On AXP systems, integer register 26 (R26). In a standard call, the return address
must be passed in this register.
return status code
See status code.
reverse video
A feature of a video terminal that reverses the default video contrast. If the
default display is black figures on a white background, reverse video displays
white figures on a black background.
RFA
See record file address.
rights database
The collection of data the system maintains and uses to define identifiers and
associate identifiers with the holders of the identifiers.
rights list
The list associated with each process that includes all the identifiers the process
holds.
RISC
See Reduced Instruction Set Computer.
RMS
See Record Management Services.
RMS–11
A set of routines that are linked with compatibility mode programs and provide
similar functional capabilities to OpenVMS Record Management Services (RMS).
The file organizations and record formats used by RMS–11 are very similar to
those of RMS.
round robin
A form of timesharing that gives images of equal priority equal access to the
CPU. The operating system uses round-robin scheduling for each of the lower 16
software priority levels. Each process at a given software priority level executes
in turn before any other process at that level (a first-in/first-out (FIFO) queue).
router
A node that can send, receive, and route packets from one node to another.

Glossary–83

routing
The network function that determines the path along which data travels to its
destination.
runaway tape condition
A situation where a tape spins unceasingly on the drive. A runaway tape
condition usually occurs because an operation does not incur a timeout condition.
The only way to recover from a runaway tape condition is to take the drive off
line.
Run-Time Procedure Library
The collection of procedures available to native-mode images at run time. These
procedures may be used by all native-mode images, regardless of the language
processor used to compile or assemble the program. These procedures also
provide support routines for high-level language compilers.
RVN
See relative volume number.
RWED
The abbreviation for Read, Write, Execute, Delete, which are types of access to
data files, directory files, or volumes.
save set
A file that the Backup utility creates to save files that it backs up.
satellite node
A processor that is part of a local area VMScluster system. A satellite node
is booted remotely from the system disk of the boot server in this type of
VMScluster system. See boot server.
SBI
See synchronous backplane interconnect.
scalar
A single data item, having one value.
scalar consumer
A process executing an image that issues VAX scalar instructions only. See vector
consumer.
scaleability
How well the software or hardware product is able to adapt to future business
needs.
scatter/gather
The ability to transfer in one I/O operation data from discontiguous pages in
memory to contiguous blocks on disk, or data from contiguous blocks on disk to
discontiguous pages in memory.
scavenging
See disk scavenging.

Glossary–84

SCB
See system control block.
scheduling priority
See process priority.
screen width
The number of character positions that can be displayed on a line.
scrolling
A feature of a video terminal that allows the display of more than one screenful
of text by vertical movement. For example, when the TYPE command is entered,
new output appears at the bottom of the screen as the oldest output disappears
off the top.
SCS
See system communications services.
search list
A logical name in which the equivalence name has multiple values instead of a
single value. A common use of a search list is to examine multiple directories to
locate a file.
search string
A group of characters defined in a command as the object of a search operation.
secondary password
A user password that may be required at login time, immediately after the
primary password has been correctly submitted. Primary and secondary
passwords can be known by separate users, to ensure that more than one user is
present at the login. A less common use is to require a secondary password as a
means of increasing the password length so that the total number of combinations
of characters makes infiltrating a system by password more time consuming.
secondary processor
The processor or processors in a symmetric multiprocessing system that do not
have the initialization and timekeeper responsibilities of the primary processor.
secondary storage
Random-access mass storage that is implemented on disks.
secondary vector
A location that identifies the starting address of a condition handler to be
executed when a condition occurs and when either the primary vector contains
0 or the handler to which the primary vector points chooses not to handle the
condition.

Glossary–85

section
A portion of process virtual memory that has common memory management
attributes (protection, access, cluster factor, and so on). It is created from an
image section, a disk file, or as the result of a Create Virtual Address Space
system service. See global section, private section, image section, and program
section.
secure terminal server
A piece of software designed to ensure that users can only log in to terminals that
are already logged out. When the user presses the Break key on a terminal, the
secure server (if enabled) responds by first disconnecting any logged in process
and then initiating a login. If no process is logged in at the terminal, the login
can proceed immediately.
security alarm
A message sent to operator terminals that are enabled to receive security class
event messages. Security alarms are triggered by the occurrence of an event
previously designated as worthy of the alarm because of its security implications.
security audit
An auditing message written to the security audit log file. These messages report
the occurrence of events with security implications, such as logins, breakins, and
changes to the authorization database. A system administrator uses the log file
to examine system activity for possible security violations or improper use of the
system.
security auditing
See auditing.
security object
A protected object to which the system controls access. See object.
security operator terminal
A class of terminal that has been enabled to receive messages sent by the
operator communication manager (OPCOM) to ‘‘security operators.’’ These
messages are security alarm messages. Normally such a terminal is a hardcopy
terminal in a protected room, so that the output provides a log of security-related
events and details that identify the source of the event.
selective crash dump
A crash dump that saves only those portions of physical memory critical to an
analysis of system failure.
semaphore
In a DECnet for OpenVMS network, a common data structure used to control the
exchange of signals between concurrent processes.
sequential access mode
The retrieval or storage of records where a program reads or writes records one
after the other in the order in which they appear, starting and ending at any
arbitrary point in the file.

Glossary–86

sequential file organization
A file organization in which records appear in the order in which they were
originally written. The records can be fixed length or variable length. Sequential
file organization permits sequential record access and random access by the
record’s file address. Sequential file organization with fixed-length records also
permits random access by relative record number.
served device
A device whose local node makes it available to other nodes in the VMScluster
system.
server
A computing system entity that provides a service to other system entities called
clients.
shadow set
One or more disk volumes of the same device type and the same physical LBN
geometry that are united for volume shadowing and represented by a virtual
unit. Thus, the term shadow set refers to the physical units and the virtual unit.
shadow set member
A physical disk mounted as part of a shadow set. Normally, shadow set members
are consistent with each other both structurally and in content.
shareable image
An image that has all of its internal references resolved, but must be linked with
one or more object modules to produce an executable image. A shareable image
cannot be executed. A shareable image file can be used to contain a library of
routines. A shareable image can be used to create a global section by the system
manager.
shared image
An image that is installed so that multiple users in a system can share the
memory pages where the image is loaded.
shared memory
A generic term referring to any memory that can be accessed by two or more
concurrent processes. In a symmetric multiprocessing system, a single copy of the
operating system resides in memory. Each processor in the system can access this
memory, as can any process executing on any processor. See multiport memory.
shell process
A predefined process that the job controller copies to create the minimum context
necessary to establish a process.
shrinking the working set
An alternative available to the swapper process to obtain pages in physical
memory. The swapper will shrink the size of the working set of selected processes
to obtain pages in physical memory. See swapping.

Glossary–87

signal
(1) An electrical impulse conveying information.
(2) The software mechanism used to indicate that an exception condition was
detected.
(3) In threads, a mechanism used to wake only one thread waiting for a condition
variable. See broadcast.
single point of failure
A portion of a computing system that, if it fails, causes the system to cease
providing service.
sink node
A node on which logging sink types, such as a file or console, are actually located.
slave terminal
A terminal that sends and receives I/O from an image and directly from
the operating system. It is not possible to enter commands to the command
interpreter from a slave terminal.
small process
A system process that has no control region in its virtual address space and has
an abbreviated context. Examples are the working set swapper and the null
process. A small process is scheduled in the same manner as user processes but
must remain resident until it completes execution; that is, it cannot be swapped.
SMP
See symmetric multiprocessing.
software
The collection of images, procedures, rules, and documentation associated with
the operation of a particular computer system. For example, the operating
system is software.
software-based fault tolerance
The ability to detect, isolate, and bypass faults that are executed through
software.
software context
Information, residing in the control blocks, that describes the software status
of a process. Examples of software context are page tables and the user’s
identification number. See software process control block.
software interrupt
An interrupt generated on interrupt priority levels 1 through 15, which can be
requested only by software.
software priority
See process priority and queue priority.

Glossary–88

software process control block (software PCB)
The data structure used to contain a process’s software context. The operating
system defines a software PCB for every process when the process is created.
The software PCB includes the following kinds of information about the
process: current state, storage address if it is swapped out of memory, unique
identification of the process, and address of the process header (which contains
the hardware PCB). The software PCB resides in system region virtual address
space. It is not swapped with a process.
sorting
The ordering of records in a prescribed sequence.
source file
A text file containing material suitable for translation into an object module by
an assembler or compiler. Such files cannot be run or linked.
source member
Any shadow set member that is in a consistent state and can be a source for full
copy or merge operations. During full copy operations, the shadowing software
reads data from source members and copies the data to inconsistent members to
bring them into full shadow set membership. All shadow sets must have at least
one source member.
source program
A program that expresses an algorithm in a programming language such as
FORTRAN, COBOL, or assembly language.
source task
The task that initiates a logical link connection request in a task-to-task
communication environment.
SP
See stack pointer.
spanned record
A record that can cross block boundaries. A spanned record consists of one or
more data segments. The position of a segment within the record and the length
of the segment is denoted by the segment control word, the first five characters of
each segment.
specification file
A command file used in the Sort/Merge utility to specify the commands and
qualifiers needed to complete a sort operation.
spin lock
In a symmetric multiprocessing system, a semaphore associated with a set
of system structures, fields, or registers whose integrity is critical to the
performance of a specific operating system task. There are two types of spin
lock: static and dynamic. Static spin locks are assembled permanently into the
system; the same static spin locks exist in the same memory locations in all
multiprocessing systems. A fork lock is a form of static spin lock. Dynamic spin
locks are created as required by the I/O configuration of a system; as a result,

Glossary–89

the set of dynamic spin locks differ from processor to processor. A device lock is a
form of dynamic spin lock. See fork lock and device lock.
spin wait
In a symmetric multiprocessing system, an execution loop performed by a
processor attempting to acquire a spin lock already owned by another processor
in the system. This activity is also known as a busy wait.
spooling
The technique of using a high-speed mass storage device to buffer data passing
between low-speed I/O devices and high-speed memory. Output spooling is the
method by which output to a low-speed peripheral device (such as a line printer)
is placed into queues maintained on a high-speed device (such as disk) to await
transmission to the low-speed device. Input spooling is the method by which
input from a low-speed peripheral (such as the card reader) is placed into queues
maintained on a high-speed device (such as disk) to await transmission to a job
processing that input.
spool queue
The list of files, supplied by processes, that are to be processed by a symbiont.
For example, a line printer queue is a list of files to be printed on the line printer.
SPT
See system page table.
SSP
See supervisor-mode stack pointer.
stack
An area of memory set aside for temporary storage or for procedure and interrupt
service linkages. A stack uses the last-in/first-out (LIFO) concept. As items are
added to (‘‘pushed on’’) the stack, the stack pointer (SP) decrements. As items are
retrieved from (‘‘popped off’’) the stack, the SP increments.
stack frame
See call frame.
stack pointer (SP)
On VAX systems general register 14 (R14) and on AXP systems integer register
30 (R30), SP contains the address of the top (lowest address) of the processordefined stack. On VAX systems, reference to SP accesses one of the five possible
stack pointers—kernel, executive, supervisor, user, or interrupt—depending on
the value in the current mode and interrupt stack bits in the processor status
longword. On AXP systems, there is no interrupt stack.
standalone BACKUP
A version of the Backup utility that is booted into memory and runs without the
control of the operating system.
standalone system
A computer system that is not incorporated into a network or VMScluster system.

Glossary–90

standard call
Any transfer of control to a procedure by any means that presents the called
procedure with the environment defined by this document and does not place
additional restrictions, not defined by the OpenVMS Calling Standard, on the
called procedure.
start I/O routine
The routine in a device driver that is responsible for obtaining necessary
resources (for example, the controller data channel) and activating the device
unit.
state
The functions that are currently valid for a given network component. States
include line, circuit, local node, module, data terminal equipment (DTE), and
logging.
state queue
A list of processes in a particular processing state. The scheduler uses state
queues to keep track of processes’ eligibility to execute. State queues include
processes waiting for a common event flag, suspended processes, and executable
processes.
static load balancing
A method of work distribution in which every process in an application is
preassigned to a processor during process creation.
status
A display type for the Network Control Program (NCP) commands SHOW and
LIST. Status refers to dynamic information about a component that is kept in
either the volatile or permanent database.
status code
A longword value that indicates the success or failure of a specific function. For
example, system services always return a status code in general register R0 upon
completion.
steady state
A shadow set is in a steady state when all its members are consistent and there
is no full copy operation or merge operation in progress to any members of the
set.
store through
See write through.
stream
An access window to a file associated with a record access control block,
supporting record operation requests.
stream record format
Property of a file specifying that the data in the file is interpreted as a continuous
sequence of bytes, without control information. Stream record format applies to
sequential files only.

Glossary–91

string
A connected sequence of characters. When a text editor searches for a word or
phrase in a text file, it is looking for a string. The character sequence that forms
a command is often called a command string.
string search buffer
A storage area used to store a connected sequence of characters being searched
for.
strong definition
Definition of a global symbol that is explicitly available for reference by modules
linked with the module in which the definition occurs. The linker always lists
a global symbol with a strong definition in the symbol portion of the map. The
librarian always includes a global symbol with a strong definition in the global
symbol table of a library. See weak definition.
strong reference
A reference to a global symbol in an object module that requests the linker to
report an error if it does not find a definition for the symbol during linking. If a
library contains the definition, the linker incorporates the library module defining
the global symbol into the image containing the strong reference.
stub
A temporary section of code that is used during the testing phase of writing
command procedures. A stub usually outputs a message stating the procedure it
is replacing.
subdirectory
A directory file, cataloged in a higher-level directory, that lists additional files
belonging to the owner of the directory.
subprocess
A subsidiary process created by another process. The process that creates a
subprocess is its owner. A process and its subprocesses share a pool of quotas and
limits. When an owner process is removed from the system, all its subprocesses
(and their subprocesses) are also removed.
subroutine
(1) A subsidiary routine that executes when called by another program. A
subroutine is often called repeatedly until a certain condition is met.
(2) On VAX systems, a routine entered by means of a JSB or BSB instruction.
See procedure.
substate
An intermediate circuit state that is displayed for a circuit state display when the
Network Control Program (NCP) commands SHOW or LIST are entered.
summary
The default display type for the Network Control Program (NCP) commands
SHOW and LIST. A summary includes the most useful information for a
component, selected from the status and characteristics information.

Glossary–92

supervisor mode
The third most privileged processor access mode (mode 2). The operating system’s
command interpreter runs in supervisor mode.
supervisor-mode stack pointer (SSP)
The process context stack pointer for supervisor mode.
suspension
A state in which a process is inactive but known to the system. A suspended
process becomes active again when another process requests the operating system
to resume it. It also becomes active to service executive mode and kernel mode
ASTs. See hibernation.
SVA
See system virtual address.
swap mode
A process execution state that determines the eligibility of a process to be
swapped out of the balance set. If process swap mode is disabled, the process
working set is locked in the balance set.
swapper
The process that performs systemwide memory scheduling. The swapper writes
modified pages to secondary storage, creates a shell for new processes, shrinks
the physical size of inactive processes, removes processes from the balance set,
and brings processes waiting for execution into the balance set.
swapping
The method for sharing memory resources among several processes by writing an
entire working set to secondary storage (swap out) and reading another working
set into memory (swap in). For example, a process’s working set can be written
to secondary storage while the process is waiting for I/O completion on a slow
device. It is brought back into the balance set when I/O completes. See paging.
switch
See qualifier.
switched virtual circuit (SVC)
A temporary logical association between two DTEs (data terminal equipment)
connected to a packet switching data network (PSDN), which is analogous to
connection by a dialup line. An SVC is set up only when there is data to transmit
and is cleared when the data transfer is complete.
symbiont
A process that transfers record-oriented data to or from a device. For example,
an input symbiont transfers data from card readers to disks. An output symbiont
transfers data from disks to line printers.
symbiont manager
The function (in the system process called the job controller) that maintains spool
queues and dynamically creates symbiont processes to perform the necessary I/O
operations.

Glossary–93

symbol
An entity that when defined will represent a particular function or entity (for
example, a command string, directory name, or file name) in a particular context.
See local symbol, global symbol, and universal symbol.
symbolic debugger
See debugger.
symbol scope
The set of command procedure levels from within which the symbol can be
accessed.
symbol table
(1) The portion of an executable image that contains the definition of global
symbols used by the debugger for images linked with the /DEBUG qualifier.
(2) A table in which the DIGITAL Command Language (DCL) places local
symbols. DCL maintains a local symbol table for each command level.
symmetric multiprocessing (SMP)
A multiprocessing system configuration in which all processors have equal access
to operating system code residing in shared memory and can perform all, or
almost all, system tasks.
synchronization
A method of controlling access to some shared resource so that predictable, welldefined results are obtained when operating in a multiprocessing environment or
in a uniprocessing environment using shared data.
synchronous backplane interconnect (SBI)
The part of the hardware that interconnects the VAX processor, memory
controllers, MASSBUS adapters, and the UNIBUS adapter.
synchronous disconnect
The disconnect that occurs when a nontransparent task can issue a call to
terminate I/O operations over a logical link without deassigning the channel.
Thus, the task can use the channel for subsequent I/O operations with the same
or a different remote task.
synchronous record operation
A mode of record processing in which a user program issues a record read or
write request and then waits until that request is fulfilled before continuing to
execute.
syntax
The particular form of a command, including spelling and the order of qualifiers
and parameters. Misspelled words are the most common syntax errors.

Glossary–94

system
In the context of a protection code, identifies a set of users in a system. System
users typically have a UIC in the range 1 through 10 (octal). However, the exact
range of a system UIC is determined by the system parameter MAXSYSGROUP.
Other ways to become a system user are to have SYSPRV privilege or to be in
the same group as the owner and hold GRPPRV. System operators and system
managers are usually system users.
system address space
See system space and system region.
system communications services (SCS)
A protocol responsible for the formation and breaking of intersystem process
connections and for flow control of message traffic over those connections. System
services such as the VMScluster connection manager and the mass storage
control protocol, or MSCP, disk server communicate with this protocol.
system control block (SCB)
On VAX systems, the data structure in system space that contains all the
interrupt and exception vectors known to the system.
system-defined identifier
See environmental identifier.
system device
The random access mass storage device unit on which the volume containing the
operating system software resides.
system disk
The disk that contains the operating system. In a VMScluster environment, a
system disk is set up so that most of the files can be shared by several processors.
In addition, each processor has its own directory on the system disk that contains
its page, swap, and dump files.
system dynamic memory
Memory reserved for the operating system to allocate as needed for temporary
storage. For example, when an image issues an I/O request, system dynamic
memory is used to contain the I/O request packet. Each process has a limit on
the amount of system dynamic memory that can be allocated for its use at one
time.
system image
The image that is read into memory from disk when the system is started up.
system manager
The person responsible for the policies, procedures, and the daily operation of a
computer system. System management tasks are sometimes performed by more
than one person and might include responsibilities for cluster management.

Glossary–95

system operator
Person responsible for maintaining the system. Within small systems, the job
may be combined with that of the system manager or informally divided among
several people. The responsibilities of the operator include changing ribbons,
rebooting the system, and keeping records.
system page table (SPT)
The data structure that maps the system region virtual addresses, including the
addresses used to refer to the process page tables. The SPT contains one page
table entry (PTE) for each page of system region virtual memory. The physical
base address of the SPT is contained in the system base register.
system password
A password required by a terminal before login can be initiated at the terminal.
system queue
A queue used and maintained by operating system procedures. See state queue.
system region
The third quarter of virtual address space (the S0 region); the lowest-addressed
half of system space. Virtual addresses in the system region are shareable
between processes. Some of the data structures mapped by system region virtual
addresses are system entry vectors, the system control block (SCB), the system
page table (SPT), and process page tables.
system services
A set of routines (part of the operating system and used by images) to control
resources, allow process communication, control I/O, and perform other such
operating system functions.
system space
The highest-addressed half of virtual address space. See system region.
system virtual address (SVA)
A virtual address identifying a location in system space.
system virtual space
See system space.
SYSUAF
See user authorization file.
tape mass storage control protocol (TMSCP)
The software protocol used to communicate I/O commands between a VAX
processor and DSA-compliant tape devices on the system. Equivalent to mass
storage control protocol, or MSCP.
target node
The node that receives a memory image from another node during a downline
load; a node that loops back a test message.

Glossary–96

target task
The task that receives and processes a logical link connection request in a
task-to-task communication environment.
task
(1) In networking, an image running in the context of a process.
(2) In transaction processing, a unit of work that performs a specific function and
that a terminal user can select for processing. Tasks implement the business unit
of work. For example, a task might book an airline reservation, update a parts
inventory, or debit an account.
task specifier
Information provided to DECnet for OpenVMS software that enables it to
complete a logical link connection to a remote task. This information includes the
name of the remote node on which the target task runs and the name of the task
itself.
terminal
The general name for peripheral devices that have keyboards and video screens
or printers. Under program control, a terminal enables users to type commands
and data on the keyboard and receive messages on the video screen or printer.
Examples of terminals are the LA36 DECwriter hardcopy terminal, the VT100
video display terminal, and the VT240-series video terminal.
Terminal Fallback Facility (TFF)
A facility that provides table-driven character conversion for terminals.
terminal server
A communications device that connects terminals, modems, or printers to an
Ethernet network.
text buffer
A text editor’s storage area for text (either terminal input or file input).
TFF
See Terminal Fallback Facility.
thread
A single, sequential flow of control within a program. It is the active execution of
a designated routine, including any nested routine invocations. A single thread
has a single point of execution within it. A thread can be executed in parallel
with other threads.
thread-serial service
A reentrant system service is thread serial if it blocks the current thread and all
other threads that attempt to call the same service or other related services until
the first call returns.
thread-synchronous service
A reentrant service is thread synchronous if it blocks only the current thread and
allows other threads to execute the same operation while the current thread is
blocked.

Glossary–97

throughput
The number of transactions or jobs a computer can complete in a given period of
time.
TIE
See translated image environment.
tied account
See captive account.
tightly coupled system
A multiprocessing system configuration consisting of multiple processors sharing
a single copy of the operating system. These processors are connected so that
they can communicate and share data. See loosely coupled system.
timeout
The expiration of the time limit in which a device is to complete an I/O transfer.
The driver’s wait for interrupt request specifies the timeout limit.
timer
Two system interrupt service routines: one (the hardware clock) that maintains
the time of day and the date and another (the software timer) that scans for
device timeouts and performs time-dependent scheduling upon request.
timesharing
A method of allocating computer time in which each process gets use of the CPU
in turn. See real-time processing.
timeslicing
A mechanism by which running threads are preempted at fixed intervals.
Timeslicing ensures that every thread is allowed time to execute.
time stamp
A text string which fully specifies a date and time. For example, 29-OCT-1993
17:13:21.
TMSCP
See tape mass storage control protocol.
TP monitor
See Transaction Processing Monitor.
traceback
The system facility that examines and displays the status of the user call stack
when an image terminates abnormally.
track
A collection of blocks at a single radius on one recording surface of a disk.

Glossary–98

transaction
An exchange of information between a user and a database or file. The operations
in a transaction are treated as a group; either all of them are completed at once
or none of them is completed. A transaction is a complete process from input to
output, regardless of the number of events in between.
transaction manager
Software that coordinates the reliable completion of a transaction.
transaction processing
A technique for organizing multiple-user, high-volume, online applications that
provides control over user access and updates of data.
Transaction Processing Monitor (TP monitor)
The master control executive for controlling a transaction processing system. The
TP monitor includes a collection of software that schedules operations, allocates
resources, and controls the operation of user and system programs which perform
I/O, and updates files or databases.
A TP monitor is designed to handle medium-to-large-scale transaction processing
systems that require high levels of availability, performance, and productivity.
transfer address
The address of the location containing a program entry point (the first instruction
to execute).
transient state
A change of state. A shadow set is in a transient state if some of its members are
undergoing either a full copy operation or a merge operation.
transition time
The amount of time (experienced as a gap in user response time) that a failed
system takes to reconfigure itself following a component failure.
translated code
The native AXP object code in a translated image. Translated code includes:
•

AXP code that reproduces the behavior of equivalent VAX code in the original
image

•

Calls to the translated image environment (TIE)

translated image
An AXP executable or shareable image created by translating the object code of
an VAX image. The translated image, which is functionally equivalent to the
VAX image from which it was translated, includes both translated code and the
original image. See VAX Environment Software Translator.
translated image environment (TIE)
A native AXP shareable image that supports the execution of translated images.
The TIE processes all interactions with the native AXP system and provides an
environment similar to VAX for the translated image by managing VAX state; by
emulating VAX features such as exception processing, AST delivery, and complex
VAX instructions; and by interpreting untranslated VAX instructions.

Glossary–99

translation
The process of converting a VAX binary image to an AXP image that runs with
the assistance of the TIE on an AXP system. Translation is a static process which
converts as much VAX code as possible to native Alpha AXP instructions. The
TIE interprets any untranslated VAX code at run time.
translation buffer
An internal processor cache containing translations for recently used virtual
addresses.
translation-not-valid fault
See page fault.
transparent
The performance of functions not visible to the user. For example, when a
command is entered, the command interpreter parses the command string and
invokes the appropriate system software. The user sees only the result of the
processing, not the processing itself.
transparent failover
The ability of a computing system to reconfigure itself or switch processing to a
redundant component and continue processing without writing any user code or
taking any corrective action.
trap
An exception condition that occurs at the end of the instruction that caused the
exception. The program counter saved on the stack is the address of the next
instruction that would normally have been executed. All software can enable and
disable some of the trap conditions with a single instruction.
trap enables
Three bits in the processor status word (PSW) that control the processor’s action
on certain arithmetic exceptions.
tributary
A physical termination on a multipoint circuit that is not a control station.
tributary address
A numeric address that the control station uses to poll a tributary.
Trojan horse program
A program that gains access to otherwise secured areas through its pretext of
serving one purpose when its real intent is far more devious and potentially
damaging. When an authorized user performs a legitimate operation using a
program, the unauthorized program within it (the Trojan horse) performs an
unauthorized function.
turnkey account
See captive account.

Glossary–100

Two-Phase Commit Protocol
A protocol that DECdtm services implement to guarantee that a transaction will
have a single outcome; for example, either a transaction has a permanent effect
on a resource or has no effect. An example of a resource is a database system.
two’s complement
A binary representation for integers in which a negative number is one greater
than the bit complement of the positive number.
two-way associative cache
A cache organization that has two groups of directly mapped blocks. Each group
contains several blocks for each index position in the cache. A block of data from
main memory can go into any group at its proper index position. A two-way
associative cache is a compromise between the extremes of fully associative and
direct mapping cache organizations that takes advantage of the features of both.
type-ahead
A terminal handling technique where the user can enter commands and data
while the software is processing a previously entered command. The commands
typed ahead are not echoed on the terminal until the command processor is ready
to process them. They are held in a type-ahead buffer.
UAF
See user authorization file.
UCB
See unit control block.
UETP
See User Environment Test Package.
UFD
See user file directory.
UIC
See user identification code.
UIC identifier
An identifier in alphanumeric format that is based on a user’s identification code
(UIC). Such an identifier can appear with or without brackets.
UIC protection code
See protection code.
unblocked record
A record that is contained in a single block. No other records or parts of records
are contained in that block.
uninterrupted service
The ability of a computing system to continue providing application service
during and after component failure without interruption or perceptible pause.

Glossary–101

unit
See device unit.
unit control block (UCB)
A structure in the I/O database that describes the characteristics of and current
activity on a device unit. The unit control block also holds the fork block for its
unit’s device driver; the fork block is a critical part of a driver fork process. The
UCB also provides a dynamic storage area for the driver.
unit initialization routine
The routine that readies controllers and device units for operation. Controllers
and device units require initialization after a power failure and during the driver
loading procedure.
unit record device
A device such as a card reader or line printer.
universal symbol
A global symbol in a shareable image that can be used by modules linked with
that shareable image. Universal symbols are typically a subset of all the global
symbols in a shareable image. When creating a shareable image, the linker
ensures that universal symbols remain available for reference after symbols have
been resolved.
unwind the call stack
To remove call frames from the stack by tracing back through nested procedure
calls using the current contents of the frame pointer (FP) register and the FP
register contents stored on the stack for each call frame.
upline dump
A DECnet for OpenVMS function that allows an adjacent node to dump its
memory to a file on a system.
urgent interrupt
An interrupt received on interrupt priority levels 24 through 31. These can be
generated only by the processor for the interval clock (in certain VAX systems),
serious errors, and power failure.
user authorization file (UAF)
The file that holds details of each account on the system. It contains the user
name, password, user identification code (UIC), quotas, limits, and privileges
assigned to each account.
User Environment Test Package (UETP)
A collection of routines that verify that the hardware and software systems are
complete, properly installed, and ready to use.
user file directory (UFD)
A file that briefly catalogs a set of files stored on disk or tape. The directory
includes the name, type, and version number of each file in the set. It also
contains a unique number that identifies that file’s actual location and points to a
list of its file attributes. See directory.

Glossary–102

user identification code (UIC)
A 32-bit value assigned to users that tells what group users belong to on the
system and what their unique identification is within that group. Any UIC
specification is enclosed in brackets, but it can be in either an alphanumeric or
a numeric format. For example, the UIC [SALES,JONES] identifies Jones as a
member of the Sales group. Protected objects like files also have UICs. In most
cases, their UICs come from the users who created them.
user mode
The least privileged processor access mode (mode 3). User processes and
Run-Time Library (RTL) procedures run in user mode.
user-mode stack pointer (USP)
The process context stack pointer for user mode.
user name
The name a user types on a terminal to log in to the system. Together with a
password, the user name identifies and authenticates a person as a valid user of
the system.
user number
See member number.
user password
See password.
user privileges
The privileges granted a user by the system manager. See process privileges.
USP
See user-mode stack pointer.
utility
A program that provides a set of related general-purpose functions, such as a
program development utility (an editor, a linker), a file management utility (file
copy or file format translation program), or operations management utility (disk
quotas, diagnostic program).
value return registers
The general registers R0 and R1 used by convention to return function values.
These registers are not preserved by any called procedures. They are available as
temporary registers to any called procedure. All other registers (R2 through R11,
AP, FP, SP, PC) may be preserved across procedure calls.
variable-length bit field (VBF)
A set of 0 to 32 contiguous bits located arbitrarily with respect to byte boundaries.
A variable bit field is specified by four attributes: the address A of a byte; the bit
position P of the starting location of the bit field with respect to bit 0 of the byte
at address A; the size, in bits, of the bit field; and an indication whether the field
is signed or unsigned.

Glossary–103

variable-length record format
A file format in which records may be of different lengths.
variable-length with fixed-length control field (VFC) record format
A file format in which records of variable length contain an additional fixedlength control area. The control area may be used to contain file line numbers
and print format controls.
VAXBI
The part of the VAX 8200, VAX 8250, VAX 8300, VAX 8350 hardware that
connects I/O adapters with memory controllers and the processor. In VAX 8530,
VAX 8550, VAX 8700, or VAX 8800 systems, or VAX 6200 and VAX 6300 systems,
the part of the hardware that connects I/O adapters with the bus that interfaces
with the processor and memory.
VAX
Virtual Address Extension.
VAXcluster configuration
A highly integrated organization of OpenVMS systems that communicate over
a high-speed communications path. VAXcluster configurations have all the
functions of single node systems, plus the ability to share CPU resources, queues,
and disk storage. Like a single-node system, the VAXcluster configuration
provides a single security and management environment. Member nodes can
share the same operating environment or serve specialized needs.
VAX Environment Software Translator (VEST)
A software migration tool that translates VAX executable and shareable
images into translated images that run on AXP systems. VEST is part of the
DECmigrate tool set. See translated image.
VAX Vector Instruction Emulation Facility (VVIEF)
A standard feature of the operating system that allows vectorized applications
to be written and debugged in a VAX system in which vector processors are not
available. VVIEF emulates the VAX vector processing environment, including
the nonprivileged VAX vector instructions and the vector system services. Use of
VVIEF is restricted to user mode code.
VBF
See variable-length bit field.
VBN
See virtual block number.
VCB
See volume control block.

Glossary–104

vector
(1) A storage location (known as an interrupt or exception vector) that contains
the starting address of a procedure to be executed when a given interrupt or
exception occurs. The system defines separate vectors for each interrupting
device controller and for classes of exceptions. Each system vector is a longword.
(2) For the purposes of exception handling, users can declare up to two software
exception vectors (primary and secondary) for each of the four access modes.
Each vector contains the address of a condition handler.
(3) A one-dimensional array.
(4) A group of related scalar values, or elements, all of the same data type.
vector capability
A software abstraction by which the operating system makes system vector
processing resources available to a process. A system manager can restrict the
use of the vector processor to users holding a particular identifier by associating
an access control list (ACL) with the CAPABILITY object VECTOR.
vector-capable system
A VAX system that, in its hardware implementation, complies with the VAX
vector architecture. A vector-capable system that incorporates one or more
optional vector processors is known as a vector-present system.
vector consumer
A process executing an image that issues VAX vector instructions and, thus,
requires the VECTOR capability and has a vector context. The operating
system must schedule a vector consumer on a scalar-vector processor pair in the
VAX system. As long as it remains a vector consumer, a process is effectively
prohibited from executing on any scalar processor in the system. See scalar
consumer and marginal vector consumer.
vector context
Current vector state of a process. See vector state.
vectorized program
An application that makes use of a vector processor. There are several methods
by which an application may be vectorized. For instance, one of its modules
may have been compiled by a vectorizing compiler or call one or more vectorized
routines. VAX MACRO programs that directly issue VAX vector instructions are
also considered vectorized programs.
vector-present system
A VAX system that, in its hardware implementation, complies with the VAX
vector architecture, and incorporates one or more optional vector processors. See
vector-capable system.
vector processor
Specialized computer hardware that executes vector instructions. For example,
hardware components that implement the VAX vector architecture.

Glossary–105

vector state
The contents of the vector registers V0 through V15, the contents of the vector
control registers, the vector processor status, and the vector exception state, as
associated with a given thread of execution. A process may have several vector
states: for instance, one associated with the mainline thread of execution and
another associated with an AST service routine. The current vector state is
referred to as the vector context of a process. See vector context.
version number
(1) The field following the file type in a file specification. It begins with a
semicolon or period and is followed by a number which generally identifies it as
the latest file created of all files having the identical file specification.
(2) The number used to identify the revision level of program.
VEST
See VAX Environment Software Translator.
VFC
See variable-length with fixed-length control field (VFC) record format.
video terminal
A terminal with a video screen for accepting output. See terminal.
virtual address
A 32-bit integer (or integer sign-extended from 32 to 64 bits on AXP systems)
identifying a byte location in the process, control, and system regions of virtual
memory. The memory management hardware translates a virtual address to a
physical address. The term virtual block number (VBN) refers to the address
used to identify a virtual block on a mass storage device. See virtual address
space.
virtual address space
The set of all possible virtual addresses that an image executing in the context of
a process can use to identify the location of an instruction or data. The system
distinguishes between the physical memory required by a process and the virtual
address space that the process defines. A process’s virtual address space is the
range of memory locations that the process can address.
virtual block number (VBN)
The file-relative address of a block on a mass storage device. The first block
in a file is always virtual block 1. See logical block number and physical block
number.
virtual circuit
An association between two DTEs (data terminal equipment) connected to a
packet switching data network (PSDN), whereby they are able to interact as if a
specific circuit were dedicated to them throughout the transmission. In reality
a logical connection is established, the actual physical circuits being allocated
according to route availability, overload conditions, and so on.

Glossary–106

virtual disk
A dedicated portion of disk space allocated for storing console files when
performing save or restore operations on console media. Virtual disks eliminate
the need to create a disk or directory for the console media. Also, because the
command procedure that handles the task invokes the Exchange utility, the
conversion of the file format from RT–11 to Files–11 is done automatically.
virtual I/O functions
A set of I/O functions that must be interpreted by an ancillary control process.
virtual memory
The set of storage locations in physical memory and on disk that is referred to
by virtual addresses. From the programmer’s viewpoint, the secondary storage
locations appear to be locations in physical memory. The size of virtual memory
in any system depends on the amount of physical memory available and the
amount of disk storage used for nonresident virtual memory.
virtual memory boot (VMB)
The primary bootstrap program that initializes a the system. The program is
located in the boot block of physical memory and is the first program read by the
CPU when a processor is booted after it has been halted.
virtual page number (VPN)
The virtual address of a page of virtual memory.
virtual unit
The shadowing software-created representation of the devices that compose a
shadow set. The virtual unit receives and directs I/O requests to the shadow set
members.
VMB
See Virtual Memory Boot.
VMS
Virtual Memory System.
VMS Lock Manager
See lock manager.
VMScluster configuration
A highly integrated organization of OpenVMS AXP systems, or a combination of
AXP or VAX systems, that communicate over a high-speed communications path.
VMScluster configurations have all the functions of single node systems, plus
the ability to share CPU resources, queues, and disk storage. Like a single-node
system, the VMScluster configuration provides a single security and management
environment. Member nodes can share the same operating environment or serve
specialized needs.
volatile database
A memory image that contains information about network management
components.

Glossary–107

volume
A mass storage media such as a disk pack or reel of magnetic tape. The volume
is the largest logical unit of the file structure.
volume control block (VCB)
A data structure that contains the information needed to control access to a
volume. It is created when the volume is mounted.
volume set
The file-structured collection of data residing on one or more mass storage media.
volume shadowing
The process of maintaining multiple copies of the same data on two or more disk
volumes. When data is recorded on more than one disk volume, you have access
to critical data even when one volume is unavailable.
VPN
See virtual page number.
VVIEF
See VAX Vector Instruction Emulation Facility.
wait for interrupt request
A request made by a driver’s start I/O routine after it activates a device. The
request causes the driver fork process to be suspended until the device requests
an interrupt or the device times out.
waiting
Becoming inactive. A process enters a process wait state when the process
suspends itself, hibernates, or declares that it needs to wait for an event,
resource, mutex, and so forth.
waking
Activating a hibernating process. A hibernating process can be awakened by a
time-scheduled wake-up call.
watchpoint
A watchpoint is a memory address, register, or (typically) a variable declared in a
program whose value is monitored during program execution.
WCB
See window control block.
WCS
See writable control store.
WDCS
See writable diagnostic control store.

Glossary–108

weak definition
Definition of a global symbol that is not explicitly available for reference by
modules linked with the module in which the definition occurs. The librarian
does not include a global symbol with a weak definition in the global symbol
table of a library. Weak definitions are often used when creating libraries to
identify those global symbols that are needed only if the module containing them
is otherwise linked with a program. See strong definition.
weak reference
A reference to a global symbol that requests the linker not to report an error
or search the default library’s global symbol table to resolve the reference if the
definition is not in the modules explicitly supplied to the linker. Weak references
are often used when creating object modules to identify those global symbols that
may not be needed at run time.
wildcard character
A nonalphanumeric character such as an asterisk or percent sign that is used
within, or in place of, a file name, file type, directory name, or version number in
a file specification to indicate ‘‘all’’ for the given field.
window
(1) See mapping window.
(2) A range of packets authorized for transmission across an X.25 data terminal
equipment/data circuit-terminating equipment (DTE/DCE) interface. The lowest
sequence number in the window is referred to as the lower window edge (0 when
the virtual circuit is just established). The packet send sequence number of the
first data packet not authorized to cross the interface is the value of the upper
window edge (that is, the lower window edge plus the window size).
window control block (WCB)
A data structure that stores access control information for a file. It is created
when a file is accessed on a volume. It is deleted when the file is closed.
word
Two contiguous bytes (16 bits) starting on an addressable byte boundary. Bits
are numbered from the right, 0 through 15. A word is identified by the address
of the byte containing bit 0. When interpreted arithmetically, a word is a
two’s complement integer with significance increasing from bit 0 to bit 14. If
interpreted as a signed integer, bit 15 is the sign bit. The value of the integer
is in the range –32,768 to 32,767. When interpreted as an unsigned integer,
significance increases from bit 0 through bit 15 and the value of the unsigned
integer is in the range 0 through 65,535.
word granularity
A property of memory systems in which adjacent words can be written
concurrently and independently by different processes or processors.
working set
The set of pages in process space to which an executing process can refer without
incurring a page fault. The working set must be resident in memory for the
process to execute. The remaining pages of that process, if any, are either in
memory and not in the process working set or they are on secondary storage.

Glossary–109

working set swapper
See swapper.
world
A category of users whose access rights to an object are identified in the last field
of a protection code. The world category encompasses all users or applications on
the system, including system operators, system managers, and users both in the
owner’s group and any other group.
writable control store (WCS)
A hardware component of certain VAX processors that allows a customer to
customize selected machine functions.
writable diagnostic control store (WDCS)
A hardware component of certain VAX processors that contains basic instruction
microcode and diagnostic microcode.
writable global section
A data structure (for example, FORTRAN global common) or shareable
image section potentially available to all processes in the system for use in
communicating between processes.
write access type
The specified operand of an instruction or procedure is only written during that
instruction’s or procedure’s execution.
write allocate
A cache management technique in which cache is allocated on a write miss as
well as on the usual read miss.
write back
A cache management technique in which data from a write operation to cache is
copied into main memory only when the data in cache must be overwritten. This
results in temporary inconsistencies between cache and main memory. See write
through.
writing
The act or capability of an image to send data. For example, when a PRINT
command is entered, the specified file is read from wherever it is stored and then
written to the line printer.
write miss
An event in which a write operation cannot be serviced by the processor’s
hardware cache.
write through
A cache management technique in which data from a write operation is copied
in both cache and main memory. Cache and main memory data are always
consistent. See write back.

Glossary–110

X.3
A CCITT recommendation that specifies the packet assembly/disassembly (PAD)
facility in a public data network.
X.25
A CCITT recommendation that specifies the interface between data terminal
equipment (DTE) and data circuit-terminating equipment (DCE) for equipment
operating in the packet mode on public data networks.
X.28
A CCITT recommendation that specifies the data terminal equipment/data
circuit-terminating equipment (DTE/DCE) interface for a start-stop mode DTE
accessing the packet assembly/disassembly (PAD) facility in a public data network
situated in the same country.
X.29
A CCITT recommendation that specifies procedures for the exchange of control
information and user data between a packet-mode data terminal equipment
(DTE) and a packet assembly/disassembly (PAD) facility.
X.29 terminal
A terminal connected to a packet assembly/disassembly (PAD) facility.
XAB
See extended attribute block.
XQP
See extended QIO processor.
Y-connector
Hardware that joins two synchronous communications lines into a single output
line.
zone
A section of a fully configured VAXft fault-tolerant computing system that
contains a minimum of a CPU module, memory module, I/O module, and
associated devices. A VAXft system consists of two such zones with synchronized
processor operations. If one zone fails, processing continues uninterrupted
through automatic failover to the other zone.

Glossary–111