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Document:	VMS 5.0 Glossary 198804
Order Number:	AA-LA03A-TE
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VMS

VMS Glossary

Order Number AA-LA03A-TE

VMS Glossary
Order Number: AA-LA03A-TE

April 1988
This document contains definitions for commonly used terms in
documentation of the VMS operating system.

Revision/Update Information:

This revised document supersedes the
VAX/VMS Glossary, Version 4.0.

Software Version:

VMS Version 5.0

digital equipment corporation
maynard, massachusetts

April 1988
The information in this document is subject to change without notice and should
not be construed as a commitment by Digital Equipment Corporation. Digital
Equipment Corporation assumes no responsibility for any errors that may appear
in this document.
The software described in this document is furnished under a license and may be
used or copied only in accordance with the terms of such license.
No responsibility is assumed for the use or reliability of software on equipment
that is not supplied by Digital Equipment Corporation or its affiliated companies.
Copyright © 1988 by Digital Equipment Corporation
All Rights Reserved.
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requests the user's critical evaluation to assist in preparing future documentation.
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Production Note
This book was produced with the VAX DOCUMENT electronic publishing
system, a software tool developed and sold by DIGITAL. In this system,
writers use an ASCII text editor to create source files containing text and
English-like code; this code labels the structural elements of the document,
such as chapters, paragraphs, and tables. The VAX DOCUMENT software,
which runs on the VMS operating system, interprets the code to format the
text, generate a table of contents and index, and paginate the entire document.
Writers can print the document on the terminal or line printer, or they can use
DIGITAL-supported devices, such as the LN03 laser printer and PostScript®
printers (PrintServer 40 or LN03R ScriptPrinter), to produce a typeset-quality
copy containing integrated graphics.

PostScript is a trademark of Adobe Systems, Inc.

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

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

glossary

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 indexed mode: An indexed addressing mode in which the base operand
specifier is addressed in absolute mode. See also indexed addressing mode and

absolute mode.
absolute mode: A mode of address in which the program counter (PC) is used as
the register in autoincrement deferred mode. The PC contains the address of the
location containing the actual operand.
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: Validating requests for connection, login, or file-access to determine
whether or not they can be accepted. User name and password provide the most
common means of access control.
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 access control list consists of one or more entries
known as access control list entries.
access control list entry (ACE): An entry in an access control list. Access control
list entries 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. Access control lists for each object can hold numerous entries, limited only
by overall space and performance considerations.
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 are, in order from most to least privileged and protected, 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
and most system services run in kernel mode and are most protected. VMS 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 also record access mode.

Glossary-1

glossary

access type: (1) The way the processor interprets instruction operands. Access types

are read, write, modify, address, and branch. (2) The way a procedure accesses its
arguments. See also record access type.
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: A character-string name or number that identifies an individual user when

the user logs in. That name or number tells the system where the user's files are
and the type of access to other files the user has.
User accounts are either privileged or nonprivileged. Privileged users have access
to privileged system commands. Nonprivileged users are limited to everyday
operations that do not threaten the integrity of the operating system.
accounting manager: A function in the job controller system process that writes

accounting records to a system accounting log file to track job activity for user
process termination, printer and batch jobs, and so on.
account name: A string that identifies a particular account used to accumulate data on

a job's resource use. This name is the user's accounting charge number, not the user
identification code (UIC).
ACE: See access control list entry.
ACL: See access control list.
ACP: See ancillary control process.
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 ·sttOW or LIST to display information about active lines, circuits, nodes,
and logging.
active set: In a VMS 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. Compare with available set.
adapter control block (ADP): A structure in the I/O database that describes an

adapter or device. VMS creates an ADP for each UNIBUS or MASSBUS adapter,
each UNIBUS or MASSBUS device, and each device on a VAXBI bus.
address: A number used by the operating system and user software to identify a

storage location in memory. See also virtual address and physical address.
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 access type:

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 backplane
interconnect.

Glossary-2

glossary

addressing mode: The way in which an operand is specified; for example, the way
in which the effective address of an instruction operand is calculated using the
general registers. The seven general-register addressing modes are register, register
deferred, autoincrement, autoincrement deferred, autodecrement, displacement, and
displacement deferred. In addition, there are six indexed addressing modes using
two general registers and literal mode addressing. The three program counter (PC)
addressing modes are referred to as immediate (for register deferred mode using the
PC), absolute (for autoincrement deferred mode using the PC), and branch.
adjacent node: A network node connected to the local node by a single physical line.
ADP: See adapter control block.
affinity: In a VMS 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.
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 VAXcluster 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.
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
VMS 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.
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.
application: A set of tasks related by the business activity they support and controlled
as a single unit. See also transaction processing.

Glossary-3

glossary

area: (1) A region of an indexed file maintained by VMS 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 network to
support the configuration of very large networks.
argument pointer (AP): General register 12 (R12). 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.
ASM P: See asymmetric multiprocessing.
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. Contrast with

symmetric multiprocessing.
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. 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 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.
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 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-4

glossary

asynchronous system trap level (ASTLVL): 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.
attached processor: See secondary processor.
attribute: In the security context, an attribute is a field of information maintained in
the rights database that identifies a characteristic that may be accorded to a holder
of the identifier. For example, if the holder and the identifier possess the resource
attribute, the holder of that identifier can charge resources, such as disk quota, to
that identifier.
auditing: See security auditing.
authentication: The act of establishing the identity of users when they start to use the
system. VMS (and most other commercial operating systems) uses passwords as the
primary authentication mechanism.
authorization file: See user authorization file.
autodecrement indexed mode: An indexed addressing mode in which the base
operand specifier uses autodecrement mode addressing. See also indexed addressing
mode and autodecrement mode.
autodecrement mode: An addressing mode in which the contents of the selected
register are decremented, and the result is used as the address of the actual operand
for the instruction. The contents of the register are decremented according to the
size of the operand. See also addressing mode.
autoincrement deferred indexed mode: An indexed addressing mode in which
the base operand specifier uses autoincrement deferred mode addressing. See also
indexed addressing mode and autoincrement deferred mode.
autoincrement deferred mode: An addressing mode in which the specified register
contains the address of a longword that contains the address of the actual operand.
The contents of the register are incremented by 4 (the number of bytes in a
longword). If the program counter (PC) is used as the register, this mode is called
absolute mode. See also addressing mode.
autoincrement indexed mode: An indexed addressing mode in which the base
operand specifier uses autoincrement mode addressing. See also indexed addressing
mode and autoincrement mode.
autoincrement mode: An addressing mode in which the contents of the specified
register are used as the address of the operand; the contents of the register are then
incremented by the size of the operand: 1 for byte, 2 for word, 4 for longword and
floating, 8 for quadword and double floating. See also addressing mode.
automatic record locking: A VMS 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. VMS Record Management
Services (RMS) maintains locks on modified records during a recovery unit.
Glossary-5

glossary

available set: In a VMS 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. Compare with

active set.
backplane interconnect: An internal processor bus that allows IjO 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 8200/8250/8300/8350 systems), or they may be on a separate bus entirely (for
instance, in a VAX-11/780 or VAX 8600/8650/8670 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 (SBI) in
the VAX-11/780 and VAX 8600 family of systems, the CPU-to-memory interconnect
(CMI) on the VAX-11/750 processor, and the VAXBI in the VAX 8530/8550/8700
/8800 and VAX 8200/8250/8300/8350 family of systems. The MicroVAX 3000
series, MicroVAX II and MicroVAX I processors use the Q22 bus as a backplane.
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 operand address: The address of the base of a table or array referenced by
index mode addressing.
base operand specifier: The register used to calculate the base operand address of a
table or array referenced by index mode addressing.
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 AL TPRI privilege.
base register: A general register used to contain the address of the first entry in a list,
table, array, or other data structure.
batch job: A noninteractive process.
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. Compare with command procedure.
BCUG: See bilateral closed user group.
bilateral closed user group (BCUG): An optional packet switching data network
facility that restricts a pair of DTEs (data terminal equipment) to 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.
Glossary-6

glossary

binding: See linking.
bit string: See variable-length bit field.
bits per inch (bpi): The recording density of a magnetic tape; indicating how much
data can fit on one inch of the recording surface. See density.
block: (1) The smallest logically addressable unit of data that a specified device can
transfer in an 1/0 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.
block 1/0: 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.
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.
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, DUO is the boot name for device DUAO.
bootstrap block: A block in the index file of a system disk. It can contain a program
that loads the operating system into memory.
bpi: See bits per inch.
branch access type: An instruction attribute that indicates the processor does not
reference an operand address; rather, the operand is a branch displacement. The
size of the branch displacement is given by the data type of the operand.
branch mode: An addressing mode in which the instruction operand specifier is a
signed byte or word displacement. The displacement is added to the contents of
the updated program counter (PC), which is the address of the first byte beyond the
displacement, and the result is the branch address.
breach: A break in the system security that results in admittance of a person or
program to an object.
breakin attempt: An effort made by an unauthorized source to gain access to the
system. Since the first system access is achieved through logging in, breakin
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 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.
Glossary-7

glossary

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 VMS 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, VMS 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 (SBI) transfer.
buffered 1/0: An IjO 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. Contrast with direct 1/0.
bugcheck: The operating system's internal diagnostic check. The system logs the
failure and, if the bugcheck is fatal, the system ceases to function.
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.
cache memory: A small, high-speed memory placed between slower main memory
c:i.nd 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: See stack frame.
call instructions: The 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 has one call stack, and the interrupt
service context has one call stack.
capability: In a VMS 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 VMS routine
that maintains the system time can execute only on the processor that has the
timekeeper capability.
Glossary-8

glossary

captive account: A type of VMS 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 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: Comite Consultatif International Telegraphique et Telephonique. 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.
CF: Current frame pointer. See frame pointer.

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. Contrast with controller data channel. (2)
A means of transmission over a packet switching data network. For VAX Packetnet
System Interface (PSI}, a logical path between a DTE (data terminal equipment) and
a DCE (data circuit-terminating equipment) 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 1/0 database created by the Assign
1/0 Channel system service to describe the device unit to which a channel is
assigned.
channel request block (CRB): A structure in the IjO 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 also alphanumeric character.
character buffer: A temporary storage area used to store the last character deleted by
an EDT delete character operation.
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.
Glossary-9

glossary

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.
Cl: See computer interconnect.
Cl-only VAXcluster configuration: A type of VAXcluster configuration in which the
computer interconnect (Cl) device is used for most interprocessor communication.
In these configurations, a cluster node may be a VAX processor or a Hierarchical
Storage Controller (HSC)
circuit: Virtual communication paths between nodes or data terminal equipment (DTE).
Circuits operate over physical lines and are the media on which all 1/0 occurs. X.25
circuits are virtual circuits.
closed user group (CUG): An optional packet switching data network facility that
restricts two or more DTEs (data terminal equipment) 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. (4) A configuration of VAX
processors (VAXcluster configuration). See also VAXcluster configuration.

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, and 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 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 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.
command language interpreter: See command interpreter.

Glossary-10

glossary

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 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 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-1 lM 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 RSX) is required for
the RSX-1 lM environment.
compatibility mode bit (CMP): The compatibility mode bit in the hardware 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.
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.

Glossary-11

glossary

computer interconnect (Cl): 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 1/0 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.
concealed device: An 1/0 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.
condition: An error state that exists when an exception occurs. See exception and

condition handler.
condition codes: The 4 bits in the 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 that uniquely identifies the exception that caused the
condition.
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 also
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 1/0 space.
congestion loss: A condition in which data packets transmitted over a network are
lost when the DECnet-VAX Routing layer is unable to buffer them.
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 1/0
space containing the vector. See also page frame number mapping.
connector node: A node that serves as an X.25 gateway to permit VMS host nodes to
access a packet switching data network.
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 hard-copy terminal connected to the central processor
console.
context: See process context.

Glossary-12

glossary

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: 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.
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 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.
control region: The highest-addressed half of per-process space (the Pl 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 (P1 BR): 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 (P1 LR): 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 (P1 PT): 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.
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.
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.
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.

Glossary-13

glossary

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.
cost: An numeric value assigned to a circuit that exists between two adjacent nodes.
In the DECnet 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.
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 also hanging.
crash dump: The action the operating system takes, when it crashes, to preserve
information for future analyis. See also complete crash dump and selective crash

dump.
CRB: See channel request block.
CRC: See cyclic redundancy check.
CRT: Cathode ray tube. See also terminal.

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 longword.
cursor: An indicator used on a video terminal to point to the screen position where the
next character will appear.
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.

Glossary-14

glossary

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 DTEs (data
terminal equipment) are connected. In non-X.25 usage, the term is synonymous
with "modem."
data link mapping (OLM): Capability of using an X.25 virtual circuit as a DECnet data
link.
data terminal equipment (DTE): An X.25 term referring to the user's equipment
(computer or terminal) connected to a DCE (data circuit-terminating equipment) 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.
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.
database: (1) All the occurrences of data described by a database management system.
(2) A collection of related data structures.
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.
DCE: See data circuit-terminating equipment.
DCL: See DIGITAL Command Language.

DOB: See device data block.
DDT: See driver dispatch table.
debug symbol table: The portion of the symbol table that is created by the compiler
or assembler.
debugger: A program that aids a programmer in finding errors in other programs.
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."
Glossary-15

glossary

deferred echo: Refers to the fact that terminal echoing does not occur until a process
is ready to accept input entered by type-ahead.
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) of magnetic tape. Typical values are 800
bpi and 1600 bpi. See bits per inch.
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.
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.
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
also pseudodevice).
device affinity: In a VMS 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 a VMS 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 allocate.
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 (DOB): 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.

Glossary-16

glossary

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 VMS 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.
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 a VMS system. It
provides a means of communication between the user and the operating system.
Contrast with 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.
direct data path: A UNIBUS adapter data path that transfers 16 bits of data in a
single synchronous backplane interconnect (SBI) transfer.
direct 1/0: 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. Contrast with 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. Contrast with fully associative

cache.
Glossary-17

glossary

direct memory access: 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 also 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 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.
displacement deferred indexed mode: An indexed addressing mode in which
the base operand specified uses displacement deferred mode addressing. See also
indexed addressing mode and displacement deferred mode.
displacement deferred mode: An addressing mode in which the specifier extension
is a byte, word, or longword displacement. The displacement is sign-extended to 32
bits and added to a base address obtained from the specified register. The result is
the address of a longword that contains the address of the actual operand. If the PC
is used as the register, the updated contents of the PC are used as the base address.
The updated contents of the PC is the address of the first byte beyond the specifier
extension.
displacement indexed mode: An indexed addressing mode in which the base
operand specifier uses displacement mode addressing. See also indexed addressing
mode and displacement mode.
displacement mode: An addressing mode in which the specifier extension is a byte,
word, or longword displacement. The displacement is sign extended to 32 bits
and added to a base address obtained from the specified register. The result is the
address of the actual operand. If the PC is used as the register, the updated contents
of the PC are used as the base address. The updated contents of the PC is the
address of the first byte beyond the specifier extension.
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.

OLM: See data link mapping.
OMA: See direct memory access.

Glossary-18

glossary

DNA: See DIGITAL Network Architecture.
double floating data: A double precision floating-Eoint number, eight bytes long,

having a range of+/- 2.9 * 10- 37 to+/- 1.7 * 10 8 and a precision of approximately
sixteen decimal digits. See also D_floating data and G_floating data.
downline system load: A DECnet-VAX 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-VAX function that allows a remote target node to

receive an RSX-11S task from another node.
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.
driver prolog table (DPT): A table in the driver that describes the driver and the

device type to the VMS procedure that loads drivers into the system.
driver start 1/0 routine: See start 1/0 routine.
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 VMS symmetric multiprocessing system
is a direct effect of the implementation of the scheduler. In a VMS multiprocessing
system, processors independently and continually look for processes to execute from
a common pool of processes.
ECB: See exit control block.
EBCDIC: See Extended Binary Coded Decimal Interchange Code.

Glossary-1 9

glossary

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.
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: 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 REI instruction.
entry point: A location that can be specified as the object of a call. It is identified
by a symbolic name and contains a mask known as the register save mask that
determines which registers are saved before the procedure is called and can enable
DV or IV arithmetic traps.
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 also 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 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.
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.

Glossary-20

glossary

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 VMS to discourage breakin attempts
whenever they seem to be in progress. VMS has a set of criteria it uses to detect the
fact that breakin attempts may be underway. Typically, once VMS 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.
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 (1/0
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 (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.
exception vector: See vector.
exception service routine: The routine by which VAX hardware initially passes
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.
Glossary-21

glossary

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
VMS Record Management Services and many of the operating system's system
service procedures execute in executive mode.
executive mode stack pointer: 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: 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.
extended attribute block (XAB): A VMS 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, 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 also 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.
F11 ACP: See Files-11 ancillary control process.
FAB: See file access block.
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.

Glossary-22

glossary

fallback: A function that the Terminal Fallback Facility (TFF) performs when an
application program sends a charater that a terminal cannot display. In this case,
TFF replaces the character with the closest possible visual character that the terminal
can display.
fault: 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.
FCB: See file control block.
FCS: See file control system.
FOL: See file definition language.
FOT: See function decision table.
FOT 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.
FIO: See file identifier.

field: A set of contiguous bytes in a logical record. See also 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 also
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
by 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 also volume.
file access block (FAB): A VMS 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 (FOL): 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 VMS 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.

Glossary-23

glossary

file identifier (Fl D): 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.
file organization: The particular file structure used as the physical arrangement of
the data comprising a file on a mass storage media. The VMS Record Management
Services (RMS) file organizations are sequential, relative, and indexed.
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.
Files-11: The name of the disk structure used by the RSX-11, IAS, and VMS
operating systems. Refer also to Files-11 Structure Level 1 and Files-11 Structure
Level 2.
Files-11 ancillary control process (Files-11 ACP): The interface process that is
the files manager for the Files-11 on-disk structure.
Files 11 Structure Level 1: The original Files-11 structure used by IAS, RSX-llM,
and RSX-11 D for disk volumes. VMS supports structure level 1 to ensure
compatibility among systems.
Files-11 Structure Level 2: The second generation disk file structure supported by
VMS.
first part of an instruction done (FPO): 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.
Glossary-24

glossary

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+/- 2.9 * 10- 37 to+/- 1.7 * 1038 and a precision of approximately seven
decimal digits.
floating underflow (FU): A trap enable bit in the processor status word (PSW).
foreign volume: Any volume other than a Files-11 formatted volume. A foreign
volume may or may not be file-structured.
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: A VMS 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 VMS 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 also 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 RO through RS
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 VMS 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 VMS fork dispatcher.
form feed: The movement of the cursor position to the start of a new page.
FP: See frame pointer.
FPO: 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 also stack frame.
frame pointer (FP): General register 13 (R13). By convention, it contains the base
address of the most recent call frame on the stack.
Glossary-25

glossary

FU: See floating underflow.

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. Contrast with direct

mapping. cache.
function code: See 1/0 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 modifier: See 1/0 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.
general register: Any of the sixteen 32-bit registers used as the primary operands of
the native-mode instructions. The general registers include 12 general purpose
registers, which can be used as accumulators, as counters, and as pointers to
locations in main memory, and the FP, AP, SP, and PC.
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+/- 0.56 * 10- 308 to +/- 0.9 * 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 change all instances of a
particular string to something else, for example, changing "fall" to "autumn."
global page table: The page table containing the master page table entries for global
sections.
global section: A data structure (for example, FORTRAN global common) or shareable
image section potentially available to all processes in the system. Access is protected
by privilege or group number of the user identification code (UIC), access control list
(ACL), or both.
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. Contrast with 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.

Glossary-26

glossary

gold key: The upper-left key on the VTlOO series terminal keypad, which enables
alternate keypad functions.
GROUP: (1) In the context SYSTEM/OWNER/GROUP /WORLD, a set of users who
have special access privileges to each other's directories and files within those
directories (unless protected otherwise). GROUP refers to all accounts having the
same group number as a particular owner. (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 first number or its alphanumeric equivalent in a user identification
code.
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.
hard-copy terminal: Terminals that print output on paper. See also terminal.
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 context: The values contained in the following registers while a process is
executing:

•

The program counter (PC)

•

The processor status longword (PSL)

•

The 14 general registers (RO through R13)

•

The four processor registers (POBR, POLR, PlBR and PlLR) that describe the
process's virtual address space

•

The stack pointer (SP) for the access mode in which the processor is executing

•

The contents to be loaded in the SP for every access mode other than the current
access mode

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).
hardware process control block (hardware PCB): 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.
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. Contrast with suspension.

Glossary-27

glossary

Hierarchical Storage Controller (HSC): A self-contained, intelligent, mass-storage
controller that communicates with VAX processors.
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 VMS operating system accomplishes the
goals of highwater marking with its erase-on-allocate strategy.
H_floating data: An extended range floating-point number, 16 bytes long, having a
range of+/- 0.84 * 10- 4932 to+/- 0.59 * 10 4932 and a precision of approximately 33
decimal digits.
holder: A user who possesses a particular identifier. The user is said to be the holder
of an identifier if he or she possesses that identifier. The rights database is the place
where the system associates users and the identifiers they hold.
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 network, a node that provides services for another node
(for example, the host node supplies program image files for a downline load). For
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 VAXcluster configuration. A host node can be
either a VAX processor that adds the device to the Mass Storage Control Protocol
(MSCP)-server database or a Hierarchical Storage Controller (HSC) server.
HSC: See Hierarchical Storage Controller.
IDB: See interrupt dispatch block.

identifier: A notation that represents a user or group of users to the system. There are
three types of identifiers: user identification code (UIC) identifiers, system-defined
identifiers, and general identifiers. Identifiers are stored in the rights database.
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.

Glossary-28

glossary

image 1/0 segment: That portion of the control region that contains the VMS Record
Management Services (RMS) internal file access blocks (If AB) 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 also

process privileges.
image section (ISECT): A group of program sections (PSECTs) 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 mode: An addressing mode in which the program counter (PC) is used as
the register in autoincrement mode addressing.
inbound connection: Logical link connection requests that a task receives.
increment: (1) To add one quantity to another. (2) The quantity added.
index: The structure that allows retrieval of records in an indexed file by key value.
See key (indexed files).
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 bit map: A table in the index file of a Files-11 volume that indicates which
file headers are in use.
index register: A register used to contain an address offset.
indexed addressing mode: An addressing mode in which two registers are used
to determine the actual instruction operand: an index register and a base operand
specifier. The contents of the index register are used as an index (offset) into a table
or array. The base operand specifier supplies the base address of the array (the
base operand address or BOA). The address of the actual operand is calculated by
multiplying the contents of the index register by the size (in bytes) of the actual
operand and adding the result to the base operand address. The addressing modes
resulting from index mode addressing are formed by adding the suffix "indexed"
to the addressing mode of the base operand specifier: register deferred indexed,
autoincrement indexed, autoincrement deferred indexed (or absolute indexed),
autodecrement indexed, displacement indexed, and displacement deferred indexed.
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.
indirect command file: See command procedure.
input stream: The source of commands and data stream, or a command procedure.

the user's terminal, the batch

instruction buffer: An 8-byte buffer in the processor used to contain bytes of the
instruction currently being decoded and to prefetch instructions in the instruction
stream. The control logic continuously fetches data from memory to keep the 8-byte
buffer full.
Glossary-29

glossary

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.
interleaving: Assigning consecutive physical memory addresses alternately between
two memory controllers.
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 also
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 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.
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): 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): The stack pointer for the system-wide interrupt stack.
interrupt vector: See vector.

1/0 database: A collection of data structures that describes I/O requests, controllers,
device units, volumes, and device drivers in a VMS 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.
1/0 driver: See device driver.
1/0 function: An I/O operation interpreted by the operating system and typically
resulting in one or more physical I/O operations.
Glossary-30

glossary

1/0 function code: A 6-bit value specified in a Queue 1/0 Request system service that
describes the particular 1/0 operation to be performed (for example, read, write,
rewind).
1/0 function modifier: A 10-bit value specified in a Queue 1/0 Request system service
that modifies an 1/0 function code (for example, read terminal input no echo).
1/0 lockdown: The state of a page when it cannot be paged or swapped out of
memory.
1/0 request packet (IRP): A structure in the IjO database that describes an individual
1/0 request. The Queue 1/0 Request system service creates an 1/0 request packet
for each 1/0 request. The VMS operating system and the driver of the target device
use information in the 1/0 request packet to process the request.
1/0 rundown: An operating system function in which the system cleans up any 1/0 in
progress when an image exits.
1/0 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.
1/0 status block (IOSB): A data structure associated with the Queue 1/0 Request
system service. This service optionally returns a status code, number of bytes
transferred, and device- and function-dependent information in an IOSB. An IOSB is
not returned from the service call, but filled in when the 1/0 request completes.
I PL: See interrupt priority level.
IRG: See interrecord gap.
IRP: See I/O request packet.

IS: See interrupt stack.
ISECT: See image section.
ISP: See interrupt stack pointer.
ISR: See interrupt service routine.

IV: Integer overflow trap enable bit in the processor status word.
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 onto 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.
journal file: A file containing the data input to the terminal for one editing session.
Glossary-31

glossary

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 1/0 drivers and the pager, run in kernel
mode.

kernel mode stack pointer (KSP): The process context stack pointer for kernel mode.
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; VMS
Record Management Services (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; VMS 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 by which the user wants to sort the
records.
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
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.
LAT: See Local Area Transport.
LAP: See link access protocol.

LBN: See logical block number.
LCN: See logical channel number.

Glossary-32

glossary

level 1 router: A DECnet 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 node that can send and receive packets, and route packets
from one node to another within its own area and between areas. Also known as an

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.

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 also 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 also quota.
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.
Glossary-33

glossary

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.
literal mode: An addressing mode in which the instruction operand is a constant value
expressed in a 6-bit field of the instruction. If the operand data type is byte, word,

longword, or quadword, the operand is zero-extended and can express values in the
range 0 through 63 (decimal). If the operand data type is floating or double floating,
the 6-bit field is composed of two 3-bit fields, one for the exponent and the other for
the fraction. The operand is extended to floating or double floating format.

LM B: 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 VAXcluster 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.
load device: The drive that holds the distribution media during software installation.
Local Area Transport (LAT): A communications protocol that the VMS operating

system uses within a local area network to communicate with terminal servers.
Local Area V AXcluster configuration: A type of VAXcluster configuration in which

cluster communication is carried out over the Ethernet by software that emulates
certain computer interconnect (CI) port functions. A VAXcluster node can be a VAX
or a MicroVAX II class processor; HSCs are not used.
local disk: A disk drive in a computer interconnect (CI) environment that is

independent of the Hierarchical Storage Controller (HSC).
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. Contrast with 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.
locality: See program locality.
locate mode: A VMS Record Management Services (RMS) record access technique

in which a program accesses records in a VMS RMS I/O buffer area to reduce
overhead. See also move mode.
lock: An association between a job and a resource maintained by the VMS Lock

Manager. A lock is normally used to synchronize access by multiple processes to
shared objects.
lock manager: See VMS Lock Manager.

Glossary-34

glossary

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 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.
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.
log: A record of performance.
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 operating system. When users log in,

they type an account name and password in response to the appropriate prompts
from the system. If the name and password match an account on the system, the
user will be permitted access to that account.
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. See also physical block number and virtual block number.
logical channel: A logical link between a data terminal equipment (DTE) and its data

circuit-terminating equipment (DCE). The physical communications line between a
DTE and DCE is divided into a set of logical channels.

Glossary-35

glossary

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 1/0 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.
Contrast with physical link. (2) A carrier of a single stream of full-duplex traffic
between two user-level processes.
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 also 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 file: A command procedure that is automatically executed at login and at the
beginning of a batch job.
longword: Four contiguous bytes (32 bits) starting on any addressable byte boundary.
Bits are numbered from right to left, 0 through 31. The address of the longword
is the address of the byte containing bit 0. When interpreted arithmetically, a
longword is a two's complement integer with significance increasing from bit 0 to
bit 30. When interpreted as a signed integer, bit 31 is the sign bit. The value of the
signed integer is in the range -2,147,483,648 to 2,147,483,647. When interpreted
as an unsigned integer, significance increases from bit 0 to bit 31. The value of the
unsigned integer is in the range 0 to 4,294,967,295.
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. Contrast with tightly coupled system.
macro: A statement that requests a language processor to generate a predefined set of
instructions.
magnetic tape ancillary control process (MTACP): The internal software process
of the operating system that interprets the logical format of VMS ANSI-labeled
volumes.
Glossary-36

glossary

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 1/0. Senders write to a mailbox, the receiver
reads from that mailbox. Some system-wide mailboxes are defined; the error logger
and operator communication manager (OPCOM) read from system-wide 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 VMS 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.
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.
Mass Storage Control Protocol (MSCP): A software protocol used to communicate
between a VAX processor and a Hierarchical Storage Controller (HSC).
MASSBUS adapter: An interface device between the backplane interconnect and the
MASSBUS.
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.
member number: The second number or its alphanumeric equivalent in a user
identification code (UIC) that uniquely identifies that code.
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.
memory mapping enable (MME): A bit in a processor register that governs address
translation.

Glossary-37

glossary

MFD: See master file directory.
Mixed Interconnect VAXcluster System: A VAXcluster environment in which both
the Ethernet and the computer interconnect (CI) are being used as interconnects.

MME: See memory mapping enable.
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 an 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 a VMS 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).
mount verification: A VMS feature that suspends 1/0 to and from volumes while
they are changing status. Mount verification also ensures that, following a
suspension in disk 1/0, 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 VMS Record Management Services (RMS) record 1/0 access technique
in which a program accesses records in its own working storage area. See also locate

mode.
MTACP: See magnetic tape ancillary control process.
MSCP: See Mass Storage Control Protocol.
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.

Glossary-38

glossary

multiport memory: A memory unit that can be connected to multiple 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.
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 VMS 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 countryspecific version of ASCII.
native image: An image whose instructions are executed in native mode.
native mode: The processor's primary execution mode, where the programmed
instructions are interpreted as byte-aligned, variable-length instructions that operate
on four data types: byte, word, longword, and quadword integers; floating and
double floating character strings; packed decimals; and variable-length bit fields.
The other instruction execution mode is compatibility mode.
NCP: See Network Control Program.
NETACP: See network ancillary control process.
network: A collection of interconnected individual computer systems.
network ancillary control program (NACP): A VMS 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.
network connect block (NCB): (1) For a DECnet 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 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.
Glossary-39

glossary

network services protocol (NSP): A formal set of conventions used in a DECnet

network to perform network management and to exchange messages over logical
links.
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 status notification:

A nontransparent task that is able to process multiple inbound
connection requests; that is, it has declared a network name or object number.

network task:

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 also 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.
node specification: The first field in a file specification. This field identifies the

location of a computer system in a network.
nonprinting character: A character in the computer code set for which there is no

corresponding graphic symbol.
nonprivileged: In DECnet-VAX terminology, 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.
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.
object: (1) A DECnet-VAX process that receives a logical link request. It performs

a specific network function or is a user-defined image for a special-purpose
application. (2) 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. (3) A system
resource such as a file, device, or directory.

Glossary-40

glossary

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 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.
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.
On-Disk Structure Level1 (ODS-1 ): See Files-11 Structure Level 1.
On-Disk Structure Level2 (ODS-2): See Files-11 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 also transaction processing.
opcode: The pattern of bits within an instruction that specifies the operation to be

performed.
OPCOM: See operator communication manager.
open account: An account that does not require a password.
operand specifier: The pattern of bits in an instruction that indicates the addressing

mode and register, or a displacement that identifies an instruction operand.
operand specifier type: The access type and data type of an instruction's operand

or operands. For example, the test instructions are of read access type because they
read only the value of the operand. The operand can be of byte, word, or longword
data type, depending on whether the opcode is for the TSTB (test byte), TSTW (test
word), or TSTL (test longword) instruction.
operating system: An integrated collection of programs that controls the execution of

computer programs and performs system functions.

Glossary-41

glossary

operator: 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.
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's console: Any terminal identified as a terminal attended by a system

operator.
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: In the context SYSTEM/OWNER/GROUP /WORLD, an owner is the

particular member (of a GROUP) to which a file, global section, mailbox, or event
flag cluster belongs.
owner process: The process or subprocess that created a subprocess.

PO: See program region.
POBR: See program region base register.
POLR: See program region length register.
POPT: See program region page table.
P1 : See control region.
P1 through PS: See parameter.
P1 BR: See control region base register.
P1 LR: See control region length register.
P1 PT: 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 4 bits are required to
represent the numbers 0 through 9.
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.

Glossary-42

glossary

packet: A unit of data to be routed from a source node to a destination node; for
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 the 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).
packet switching: A data transmission process, utilizing addressed packets, whereby
a channel is occupied only for the duration of transmission of the packet.
Packetnet System Interface (PSI): A software product that allows the VMS user to
communicate across packet switching data networks (PSDNs).
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) A set of 512 contiguous byte locations beginning at an even 512-byte
boundary used as the unit of memory mapping and protection. (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.
page fault: An exception generated by a reference to a page that is not in the working
set of the faulting process. Also called translation-not-valid fault.
page fault cluster: See cluster.
page fault cluster size: The number of pages read into memory on a page fault.
page frame number (PFN): The high-order 21 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 1/0 space (as opposed to mapping it to a disk file).
page marker: A character or characters (generally a form feed) that separates pages in
a file processed by a text editor.
page table: A memory management data base used to account for virtual pages. See
also system page table, process page table, and global 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).
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.

Glossary-43

glossary

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. On a VMS system, 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 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 Pl through PB. See also 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 VMS 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.
PCBB: See process control block base register.
peripheral device: Any unit, distinct from the CPU and physical memory, that can
provide the system with input or accept any output from it. Terminals, line printers,
and disks are peripheral devices.
permanent database: A file containing information about network management
components. See also 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.
Glossary-44

glossary

Phase II V AXcluster configuration: A VAXcluster environment in which both the

computer interconnect (CI) and the Ethernet are used for cluster communications.
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.
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 (1/0 space).
physical block number: The physical address of a block on a mass storage device.

Contrast with logical block number and virtual block number.
physical 1/0 functions: A set of 1/0 functions that allows access to all device-level

1/0 operations except maintenance mode.
physical link: A signal-carrying media that links two nodes in a network. Contrast

with 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.
Pl D: 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

VMS 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.

Glossary-45

glossary

primary processor: The processor in a VMS 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 VMS environment and
prepare memory for the entire system. In addition, the primary processor serves as
the system timekeeper. Contrast with 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.
priority: See process priority and interrupt priority level.
private section: An image section of a process that is not shareable among processes.

See also global section.
private volume: A volume that has been allocated by a process for its own exclusive

use.
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.
privileges: 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 also process privileges, user privileges, and image privileges.
procedure: A routine entered by means of a call instruction. See also command

procedure.
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 VMS 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.
process context: The set of data defining the environment, both hardware and

software, in which a process executes. See also 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 Control Block Base Register: A processor register that contains the physical

address of the current process control block (PCB).
process header: 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.

Glossary-46

glossary

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 (PIO): A 32-bit binary value that uniquely identifies a process.

Each process has a process identification and a process name.
process 1/0 channel: See channel.
process 1/0 segment: That portion of a process control region that contains the

process permanent VMS Record Management Services (RMS) internal file access
block for each open file, and the 1/0 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.
process page tables: The page tables used to describe process virtual memory.

A file that is opened or created through VMS Record
Management Services (RMS) by supervisor or executive mode when the process
permanent bit is set in the file-processing options field.

process permanent file:

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 1/0 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.
processor register: A part of the processor used by the operating system software

to control the execution states of the computer system. Processor registers 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.
processor status longword (PSL): A privileged processor register 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,
the previous access mode, the current access mode, the interrupt stack bit, the trace
trap pending bit, and the compatibility mode bit.
Glossary-4 7

glossary

processor status word (PSW): 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.
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 also image.
program counter (PC): General register 15 (R15). At the beginning of an instruction's

execution, the PC normally contains the address of a location in memory from which
the processor will fetch the next instruction it will execute.
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.
program region: The lowest-addressed half of process address space (PO region). The

program region contains the image currently being executed by the process and
other user code called by the image.
program region base register (POBR): The processor register, or its equivalent in a

hardware process control block, that contains the base virtual address of the page
table entry for virtual page number 0 in a process program region.
program region page table (POPT): The page table that maps the program region of

virtual address space ..
program region length register (POLR): The processor register, or its equivalent in

a hardware process control block, that contains the number of entries in the page
table for a process program region.
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.
programmer number: See member number.
project number: See group number or account number.
prompt: A character string appearing on a terminal indicating that the user must

provide input.
protection: The attributes of a resource that limit the type of access available to users.

Resources include volumes, devices, directories, and files. See also user identification

code and access control list.
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.
PSECT: See program section.

Glossary-48

glossary

pseudodevice: An entity treated as an 1/0 device by the user or system, although it is
not any particular physical device. A pseudodevice is a forwarding address through
which actual physical devices can always be reached.
PSDN: See packet switching data network.
PSI: See Packetnet System Interface.
PSL: See processor status longword.
PSW: See processor status word.
PTE: See page table entry.

public volume: A file-structured disk volume that contains public files.
PVC: See permanent virtual circuit.
pure code: See reentrant code.
QIO: See Queue I/O Request system service.
quadword: Four contiguous words (64 bits) starting on any addressable byte boundary.
Bits are numbered 0 to 63 from right to left. A quadword is identified by the address
of the word containing the low-order bit (bit 0). When interpreted arithmetically, a
quadword is a two's complement integer with significance increasing from bit 0 to
bit 62. Bit 63 is used as the sign bit. The value of the integer is in the range -2 63 to
263_1.

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 also state queue and
system queue. (2) To make an entry in a list or table, perhaps using the INSQUE
instruction.
Queue 1/0 Request system service: The VMS system service that handles $QIO
and $QIOW requests. The QIO prepares an 1/0 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.

Glossary-49

glossary

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 also limit.
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.
random access by record file address (RFA): The retrieval of a record by its unique

address, which is provided to the program by VMS 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 also 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.
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.
record: A set of related data that a program treats as a unit.
record access block (RAB): An VMS Record Management Services (RMS) user

control block allocated at either assembly or run time to communicate with VMS
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 VMS 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.

Glossary-50

glossary

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 IfO 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 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 also automatic
record locking and manual record locking.
Record Management Services (RMS): A set of operating system procedures that
is called by programs to process files and records within files. VMS RMS allows
programs to issue GET and PUT requests at the record level (record 1/0) as well
as read and write blocks (block IfO). VMS RMS is an integral part of the system
software; its procedures run in executive mode.
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 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.
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.
register: A storage location in hardware logic other than main memory. See also
general register, processor register, and device register.
register deferred indexed mode: An indexed addressing mode in which the base
operand specifier uses register deferred mode addressing. See also indexed addressing
mode and register deferred mode.
register deferred mode: An addressing mode in which the contents of the specified
register are used as the address of the actual instruction operand. See also addressing

mode.
register mode: An addressing mode in which the contents of the specified register are
used as the actual instruction operand.

Glossary-51

glossary

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.
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 VMS Record Management Services (RMS) with the relative record
number of the cell containing the record.
relative volume number: A volume number that uniquely identifies which volume
set contains a file.
remote device: A device that is not directly connected to the local node, but is
available through the VAXcluster system.
remote data terminal equipment (DTE): Any DTE in a network other than the one
at which the user is located.
remote node: To any one node in the network, this node is any other network node.
See also 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 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.
resume: To activate a suspended process. Contrast with wake.
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.
RMS: See Record Management Services.

Glossary-52

glossary

RMS-11 : A set of routines that are linked with compatibility mode programs and
provide similar functional capabilities to VMS Record Management Services (RMS).
The file organizations and record formats used by RMS-11 are very similar to those
of VMS RMS.
round robin: A form of time sharing that gives images of equal priority equal access

to the CPU. The VMS operating system uses round-robin scheduling for each of the
lower sixteen software priority levels. Each process at a given software priority level
executes in tum 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.
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.

SBI: See synchronous backplane interconnect.
SBR: See system base register.
scatter/gather: The ability to transfer in one 1/0 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.
SCB: See system control block.
SCBB: See system control block base register.

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.

Glossary-53

glossary

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.
The processor or processors in a VMS symmetric
multiprocessing system that do not have the initialization and timekeeper
responsibilities of the primary processor.

secondary 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.
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 VMS 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 as security

operators. Security alarms are triggered by the occurrence of an event previously
designated as worthy of the alarm because of its security implications.
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.
security auditing: The monitoring and recording of specified events occuring on the

system. These events include login failures, privileged and unprivileged access to
system objects, and changes to the system user authorization file (SYSUAF).
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 network, a common data structure used to control the

exchange of signals between concurrent processes.

Glossary-54

glossary

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.
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

VAXcluster system.
shadow set: One or more compatible physical disk volumes connected together 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,

all shadow set members contain identical data in corresponding logical blocks.
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 VMS symmetric multiprocessing system, a single
copy of the VMS operating system resides in memory. Each processor in the system
can access this memory, as can any process executing on any processor. See also

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 also swapping.
signal: (1) An electrical impulse conveying information. (2) The software mechanism

used to indicate that an exception condition was detected.
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 1/0 from an image and directly
from the operating system. It is not possible to enter commands to the command

interpreter from a slave terminal.
SLR: See system length register.

Glossary-55

glossary

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 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 also 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.
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 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.
spin lock: In a VMS 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 VMS 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, 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 VMS 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.

Glossary-56

glossary

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.
spooling: The technique of using a high-speed mass storage device to buffer data
passing between low-speed IfO 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.
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: A standard data structure built on the stack during a procedure call,
starting from the location addressed by the frame pointer (FP) to lower addresses,
and popped off during a return from procedure. Also called call frame.
stack pointer (SP): General register 14 (R14). SP contains the address of the top
(lowest address) of the processor-defined stack. Reference to SP accesses one of
the five possible stack pointers-kernel, executive, supervisor, user, or interruptdepending on the value in the current mode and interrupt stack bits in the processor
status longword.
start 1/0 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 RO upon completion.
store through: See write through.
Glossary-5 ~

glossary

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.
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. Contrast with 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.
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) A routine
entered by means of a JSB or BSB instruction. Contrast with 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.
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: 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. Contrast with hibernation.
SVA: See system virtual address.

Glossary-58

glossary

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 system-wide 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 1/0 completion on a
slow device. It is brought back into the balance set when 1/0 completes. Contrast
with 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 1/0 operations.
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.
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.
symbolic debugger: See debugger.
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.
synchronous backplane interconnect (SBI): The part of the hardware that

interconnects the 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 1/0 operations over a logical link without deassigning the
channel. Thus, the task can use the channel for subsequent 1/0 operations with the
same or a different remote task.

Glossary-SS

glossary

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.
SYSTEM: In the context SYSTEM/OWNER/GROUP /WORLD, SYSTEM refers to the

group numbers of less than or equal to 10 (octal) that are used by operating system
and its controlling users, the system operators, and the system manager.
system address space: See system space and system region.
system base register (SBR): A processor register containing the physical address of

the base of the system page table.
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 VAXcluster connection
manager, and the Mass Storage Control Protocol (MSCP) disk server communicate
with this protocol.
system control block (SCB): The data structure in system space that contains all the

interrupt and exception vectors known to the system.
system control block base register (SCBB): A processor register containing the base

address of the system control block.
system-defined identifier: One of three classes of identifiers. System-defined

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 also identifier.
system device: The random access mass storage device unit on which the volume

containing the operating system software resides.
system dynamic memory: Memory reserved for the operating system to allocate as

needed for temporary storage. For example, when an image issues an 1/0 request,
system dynamic memory is used to contain the 1/0 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 identification register: A processor register that contains the processor type

and serial number.
system image: The image that is read into memory from disk when the system is

started up.
system length register (SLR): A processor register containing the system page table

in longwords.
system manager: The person responsible for the policies, procedures, and the daily

operation of a computer system. VMS system management tasks are sometimes
performed by more than one person and might include responsibilities for cluster
management.

Glossary-60

glossary

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

also state queue.
system region: The third quarter of virtual address space (the SO 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 VMS operating system and used by

images) to control resources, allow process communication, control I/0, and to
perform other such operating system functions.
system space: The highest-addressed half of virtual address space. See also system

region.
system virtual address (SVA): A virtual address identifying a location in system

space.
system virtual space: See system space.
target node: The node that receives a memory image from another node during a

downline load; a node that loops back a test message.
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-VAX 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 hard-copy terminal, the
VTlOO 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.
Glossary-61

glossary

text buffer: A text editor's storage area for text (either terminal input or file input).
TFF: See Terminal Fallback Facility.

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. Contrast with loosely

coupled system.
timeout: The expiration of the time limit in which a device is to complete an 1/0

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.
time sharing: A method of allocating computer time in which each process gets use of

the CPU in tum. See also real-time processing.
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.
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 processing: A technique for organizing multiple-user, high-volume,

on-line 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 1/0, and updates files or databases.
ATP 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).
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.

Glossary-62

glossary

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.
turnkey account: See captive account.
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.
UBA: See UNIBUS adapter.

UBI: See UNIBUS interconnect.
UCB: See unit control block.
UETP: See User Environment Test Package.
UFO: See user file directory.

UIC: See user identification code.
unblocked record: A record that is contained in a single block. No other records or
parts of records are contained in that block.
UNIBUS adapter (UBA): An interface between the backplane interconnect to the
VAX-11/780 and the UNIBUS.
UNIBUS interconnect (UBI): An interface between the backplane interconnect to the
VAX-11/750 and the UNIBUS.
unit: See device unit.
Glossary-63

glossary

unit control block (UCB): A structure in the 1/0 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-VAX function that allows an adjacent node to dump its
memory to a file on a VMS 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): A file containing an entry for every user that the
system manager authorizes to gain access to the system. Each entry identifies the
user name, password, default account, user identification code (UIC), quotas, limits,
and privileges assigned to individuals who use the system.
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 (UFO): 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 also directory.
user identification code (UIC): A 32-bit value assigned to users and to files, global
sections, common event flag clusters, and mailboxes that specifies the type of access
(read and/or write access and, in the case of files, execute and/or delete access)
available to the SYSTEM, OWNER, GROUP, and WORLD. A UIC has two formats:
numeric and alphanumeric. The numeric UIC consists of a group identifier and
a member identifier separated by a comma and enclosed within square brackets.
These identifiers may appear as alphanumeric characters. The alphanumeric UIC
consists of a member name and, optionally, a group name.
user mode: The least privileged processor access mode (mode 3). User processes and
Run-Time Library Procedures run in user mode.
user mode stack pointer: The process context stack pointer for user mode.

Glossary-64

glossary

user name: The name that a user types on a terminal to log in to the system. See also

password.
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 RO and Rl 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 Rll, 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.
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 fixed-length control area.
The control area may be used to contain file line numbers and print format controls.
VAX.Bl: The part of the VAX 8200/8250/8300/8350 hardware that connects 1/0

adapters with memory controllers and the processor. In a VAX 8530/8550/ 8700
/8800 system, the part of the hardware that connects 1/0 adapters with the bus that
interfaces with the processor and memory.

VAX: Virtual Address Extension.
VAX.cluster configuration: A highly integrated organization of VMS 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.clusters Phase II: See Phase II VAXcluster configuration.
VBF: See variable-length bit field.
VBN: See virtual block number.
VCB: See volume control block.

Glossary-65

glossary

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.
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.
VFC: See variable-length with fixed-length control field record format.

video terminal: A terminal with a video screen for accepting output. See terminal.
virtual address: A 32-bit integer 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 also

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 VMS virtual address space seen by the programmer is a linear array
of 4,294,967,296 (2 32 ) byte addresses. The VMS 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. Contrast with 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.
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 RTl 1 to Files-11 is done automatically.
virtual 1/0 functions: A set of 1/0 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 page number (VPN): The virtual address of a page of virtual memory.
Glossary-66

glossary

virtual unit: A software-created representation of a group of disks that compose a

shadow set. Most users and system resources communicate with the virtual unit
as if it were a physical device and disk volume. A Hierarchical Storage Controller
(HSC) then manages 1/0 to the physical disks that are bound together as a shadow
set.
VMS: Virtual Memory System.
VMS Lock Manager: A VMS facility that mediates lock requests.
volatile database: A memory image that contains information about network

management components.
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: A cooperative effort between the VMS operating system and a

Hierarchical Storage Controller (HSC) to record data on more than one volume. This
duplication of data provides greater data availability and faster data accessibility.
VPN: See virtual page number.
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.
wait for interrupt request: A request made by a driver's start 1/0 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.
waking: Activating a hibernating process. A hibernating process can be awakened by

a time-scheduled wake-up call.
WCB: See window control block.
WCS: See writeable control store.
WDCS: See writeable diagnostic control store.
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. Contrast with 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.
Glossary-67

glossary

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: 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.
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.
working set swapper: See swapper.
WORLD: In the context SYSTEM/OWNER/GROUP/WORLD, WORLD refers to all

users, including the system operators, the system manager, and users both in an
owner's group and in any other group.
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 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. Contrast
with write through.
write miss: An event in which a write operation cannot be serviced by the processor's
hardware cache.
writeable control store: A hardware component of certain VAX processors that
allows a customer to customize selected machine functions.

Glossary-68

glossary

writeable diagnostic control store: A hardware component of certain VAX
processors that contains basic instruction microcode and diagnostic microcode.
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. Contrast with write back.
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 DTEs (data
terminal equipment) and DCEs (data circuit-terminating equipment) 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 DTE (data terminal equipment)
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.

Glossary-69

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