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Document:	VAX/VMS Glossary
Order Number:	AA-Z102A-TE
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Pages:	68
Original Filename:	http://bitsavers.org/pdf/dec/vax/vms/4.0/AA-Z102A-TE_VAX_VMS_4.0_Glossary_198409.pdf

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VAX/VMS
Glossary
Order Number: AA-Z 102A-TE

September 1984
This document contains definitions for commonly used terms in
documentation of the VAX/VMS operating system.

Revision/Update Information:

This is a new manual.

Software Version:

VAX/VMS Version 4.0

digital equipment corporation
maynard, massachusetts

September 1984
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 © 1984 by Digital Equipment Corporation
All Rights Reserved.
Printed in U.S.A.
The postpaid READER'S COMMENTS form on the last page of this document
requests the user's critical evaluation to assist in preparing future documentation.
The following are trademarks of Digital Equipment Corporation:
DEC
DEC/CMS
DEC/MMS
DECnet
DECsystem-10
DECSYSTEM-20
DECUS
DECwriter

DIBOL
EduSystem
IAS
MASSBUS
PDP
PDT
RSTS
RSX

UNIBUS
VAX
VAXcluster
VMS
VT

t!JD~DD~D
ZK-2302

This document was prepared using an in-house documentation production system. All
page composition and make-up was performed by TeX, the typesetting system developed
by Donald E. Knuth at Stanford University. TeX is a registered trademark of the American
Mathematical Society.

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

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

iii

Glossary

''a" character: The subset of ASCII characters that are allowed in the labels of

ANSI-labeled magnetic tape.
abort: An exception that occurs in the middle of an instruction and sometimes

leaves the registers and memory in an indeterminate state, which may prevent
the instruction from being restarted.
absolute indexed mode: An indexed addressing mode in which the base operand

specifier is addressed in 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: Values 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 connect,· 1ogin, or file-access requests to determine whether

or not they can be accepted. User name and password provide the most common
means of access control.
access control list: 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: 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: Any of the four processor access modes in which software executes.

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. When the processor is in any other mode, the
processor is inhibited from executing privileged instructions. 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 runs in kernel and executive mode and is most protected.
The command interpreter is less protected and runs in supervisor mode. The
debugger runs in user mode and is not more protected than normal user programs.
See also record access mode.

Glossary-1

Glossary

access type: (1) The way in which the processor accesses instruction operands.

Access types are read, write, modify, address, and branch. (2) The way in which a
procedure accesses its arguments. See also record access type.
access violation: An attempt to reference an address that is either not mapped into

virtual memory or not accessible by the current access mode.
account: A key to the system and a unit of system accounting. Each system user,

including parts of the system itself, has an account. The system manager creates
these accounts in the master file directory and assigns an account number to each.
Individual users are identified by an account name as well. When you log in, you
log in under a particular account name or number. This number informs the system
where your files are and what kind of access to other files and system facilities you
should be given.
User accounts are either privileged or nonprivileged. Privileged users have access to
all system commands and to all parts of the system. Nonprivileged users are limited
to everyday operations that do not threaten the integrity of the operating system.
accounting manager: The function in the system process called the job controller 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's 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 NCP commands SHOW or LIST to
display information about active lines, circuits, nodes, and logging.
adapter control block (ADP): A structure in the 1/0 database that describes either a

UNIBUS or MASSBUS adapter.
address: A number used by the operating system and user software to identify a

storage location. See also virtual address and physical address.
address access type: A type of access in which the specified operand of an

instruction is not accessed directly by the instruction. The address of the specified
operand is the actual instruction operand. The context of the address calculation is
determined by the data type of the operand.
address space: The set of all possible addresses available to a process. Virtual address

space refers to the set of all possible virtual addresses. Physical address space refers
to the set of all possible physical addresses sent out on the SBI.

2-Glossary

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 PC addressing
modes are called immediate (for register deferred mode using the PC), absolute (for
autoincrement deferred mode using the PC), and branch.
adjacent node: A network node removed from the local node by a single physical
line.
ADP: See adapter control block.
alarm: See security alarm.
allocate a device: To reserve 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 nuinber between 0 and 255 that the system manager
assigns to a pair of hosts and the dual-pathed devices that the hosts make available
to other nodes in the VAXcluster. 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 and member in alphanumeric form rather than numeric form.
alternate key: An optional key within the data records in an indexed file; used by
VAX 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. Three examples of
ACPs are the Files-11 ACP, the magnetic tape ACP, and the network ACP.
AP: See argument pointer.
area: (1) A region of an indexed file maintained by VAX RMS that allows a user to
specify placement and/ or specific bucket sizes 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: A level 1 router.

Glossary-3

Glossary

. area routing: A technique for grouping the nodes in a network into areas for routing

purposes. Routing in a multiple-area network is hierarchical, 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 DECnet to support
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 the CALL
instructions.
ASCII: See American Standard Code for Information Interchange.
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.
assign a channel: To establish the necessary software link between a user process and

a device unit that allows a user process to communicate with the device.
assignment statement: The definition of a symbol name to use in place of 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 the user 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.
asynchronous system trap level (ASTLVL): A value kept in an internal processor

register (ASTLVL) 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 will not be serviced while the processor is executing in a more
privileged access mode.
attached processor: The secondary processor in a VAX-11/782. See primary

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.
4-Glossary

Glossary

auditing: The act of noting the occurrence of an event that has security implications.
authentication: The act of establishing the identity of users when they start to use the

system. VAX/VMS (and most other commercial operating systems) use 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.
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
data type context of the register: 1 for byte, 2 for word, 4 for longword and floating,
8 for quadword and double floating.
autoincrement deferred indexed mode: An indexed addressing mode in which the

base operand specifier uses autoincrement deferred mode addressing.
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 PC is used as the register, this mode is called absolute mode.
autoincrement indexed mode: An indexed addressing mode in which the base

operand specifier uses autoincrement mode addressing.
autoincrement mode: An addressing mod~ 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.
automatic record locking: A VAX 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. RMS maintains locks on modified records during a recovery
unit.
backplane interconnect: An internal processor bus that UNIBUS and MASSBUS

adapters use to communicate with the central processor and main memory. The
backplane interconnect is called the synchronous backplane interconnect (SBI) on
the VAX-11/780 processor and is called the memory interconnect on the VAX-11
/750 processor.
balance set: The set of all process working sets currently resident in physical memory.

The processes whose working sets are in the balance set have memory requirements
that balance with available 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.
Glossary-5

Glossary

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 ALTPRI.
base register: A general register used to contain the address of the first entry in a list,

table, array, or other data structure.
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.
Compare with command procedure.
bilateral closed user group (BCUG): An optional packet switching data network

facility that restricts a pair of DTEs to communicating with each other.
binary machine code: The internal instruction format actually used by the computer.
It is called binary because only two characters-0 and 1-are used in this code.

Users rarely see binary machine code. Although it is the only form that the
computer can use, it is difficult for people to use. Thus, programmers use languages,
compilers, and the assembler to generate the binary code.
binding: See linking.
bit string: See variable-length bit field.
bits per inch (bpi): The recording density of a magnetic tape; indicating how many

characters 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 designed to bring

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 itself 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.

6-Glossary

Glossary

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 which indicates that the processor does
not reference an operand address, but that 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 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: A special type of multicast addressing, in which all nodes are
to receive a message.
broadcast circuit: A circuit on which multiple nodes are connected and on which
exists a method for transmitting a message that will be received by multiple
receivers.
bucket: A storage structure of 1 to 32 blocks used for building and processing files of
relative and indexed organization. A bucket contains one or more records or record
cells. Buckets are the unit of contiguous transfer between VAX 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, VAX 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 SBI transfer.
buffered 1/0: See system-buffered 1/0.
bugcheck: The operating system's internal diagnostic check. The system logs the
failure and crashes the system.

Glossary-7

Glossary

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

and the processor. A cache increases effective memory transfer rates and processor
speed. It contains copies of data recently used by the processor and fetches several
bytes of data from memory in anticipation that the processor will access the next
sequential series of bytes.
call: To transfer control to a specified routine.
call frame: 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 conventional stack structure used during a procedure call.

Each access mode of each process context has one call stack, and interrupt service
context has one call stack.
captive accounts: A type of VAX/VMS account that limits the activities of the

user. Typically, the user is restricted to using certain command procedures and/or
commands. 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 DECnet 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.
CF: Current 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. See also controller data channel. (2) A
means of transmission over a packet switching data network. For VAX PSI, a logical
path between a DTE and a DCE over which data is transmitted. Each channel is
identified by a unique reference number called a logical channel number (LCN).
channel control block (CCB): A structure in the 1/0 database created by the Assign

1/0 Channel system service to describe the device unit to which a channel is
assigned.
8-Glossary

Glossary

channel request block (CRB): A structure in the I/O database that describes the
activity on a particular controller. The channel request block for a controller contains
pointers to the wait queue of drivers ready to access a device through the controller.
character: A symbol represented by an ASCII code. See also alphanumeric character.
character buffer: A temporary storage area used to store the last character deleted by
an EDT delete character operation.
character editing: Editing text at the character level; an operational mode of EDT,
entered through the CHANGE command.
character string: A contiguous set of bytes. A character string is identified by
two attributes: an address and a length. Its address is the address of the byte
containing the first character of the string. Subsequent characters are stored in bytes
of increasing addresses. The length is the number of characters in the string.
character string descriptor: A quadword data structure used for passing character
data (strings). The first word of the quadword contains the length of the character
string. The second word can contain type information. The remaining longword
contains the address of the string.
characteristics: A display type for the 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.
circuit: Virtual communication paths between nodes or DTEs. Circuits operate over
physical lines and are the medium on which all I/O occurs. X.25 circuits are virtual
circuits.
closed user group (CUG): An optional packet switching data network facility that
restricts two or more DTEs in the same group to communicating with each other.
The basic CUG also prevents these DTEs from accessing or being accessed by other
DTEs outside the group. Additions to the basic CUG facility allow one or more
DTEs to access or be accessed by DTEs outside the group.
cluster: (1) A set of contiguous blocks that is the basic unit of space allocation on
a Files-11 disk volume. (2) A set of pages brought into memory in one paging
operation. (3) An event flag cluster. (4) A configuration of VAX processors.
CMI: See computer memory interconnect.
CM P: The compatibility mode bit in the hardware processor status longword.

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 DECnet to its Data Link
layer to indicate that one or more stations (nodes) are contending with the local
station's transmission.

Glossary-9

Glossary

command: An instruction, generally an English word, typed by the user at a terminal
or included in a command procedure that requests the software monitoring a
terminal or reading a command procedure to perform some well-defined activity.
For example, typing 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 typed by the user at a terminal or submitted in a command file.
command level: Input stream for the command interpreter. The initial input stream
is always command level 0. Each subsequent execution of a procedure changes the
command level.
command node: The node from which an 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 typing 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-llM execution environment
for an RSX-llM task image. The operating system compatibility mode procedures
intercept calls to the RSX-1 lM executive and convert them to the appropriate
operating system functions.
compiler: A system component that translates a program written in a high-level
language into an object module in binary machine code.

10-Glossary

Glossary

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 NCP command syntax.
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 that contains files that provide information about
networking 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/status register 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 page frame number mapping.
connector node: A node that serves as an X.25 gateway to permit VAX/VMS host
nodes to access a packet switching data network.
console: The manual control unit integrated into the central processor. The console
includes a serial line interface connected to a hard-copy terminal, which enables the
operator to start and stop the system, monitor system operation, and run diagnostics.
console terminal: The hard-copy terminal connected to the central processor console.
context: The environment of an activity. See also process context, hardware context,
and software context.

Glossary-11

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 PCB using the Save Process Context instruction, loads the
hardware PCB of another process into the hardware context using the Load Process
Context instruction, scheduling that process for execution.
contiguous area: A group of physically adjacent blocks.
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 station: The network node at the controlling end of a multipoint circuit. The

control station controls the tributaries for that circuit.
control/status register (CSR): A control/status register for a device or controller. It

resides in the processor's I/O space.
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.
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.

12-Glossary

Glossary

cost: An integer value assigned to a circuit between two adjacent nodes. According to
the routing algorithm, 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: An acronym for central processing unit. The CPU is 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.
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. There is no concrete indication of a system crash at a
user terminal; if the system has crashed, however, users will be unable to use their
terminals. See also hanging.
CRB: See channel request block.
CRC: Cyclic redundancy check.
CRT: Cathode ray tube. See also terminal.
CSR: See Control/Status Register.
CUG: See closed user group.

current access mode: The processor access mode of the currently executing software.
The current mode field of the processor status longword indicates the access mode
of the currently executing software.
cursor: A flashing indicator used on video terminals to point to the screen position
where the next character will appear.
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.
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 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 on a packet switching data network for
the purpose of sending and/ or receiving data.

Glossary-13

Glossary

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.

debugger: See symbolic debugger.
decryption: The process that restores encoded information to its original unencoded
form.
dedicated: A system resource-an 1/0 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."
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 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.
14-Glossary

Glossary

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 parent process of a tree of
subprocesses. Detached processes are created by either the job controller when a
user logs on the system, when a batch job is initiated, or when a logical link connect
is requested. The job controller does not own the user processes it creates; these
processes are therefore detached.
device: The general name for any peripheral hardware 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 pseudo device.
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/controller name and driver name for a set of devices attached to the same
controller.
device driver: The software associated with each physical device in the system that
serves as the interface between the operating system and the device controller.
device interrupt: An interrupt received on interrupt priority levels 16 through 23.
Device interrupts can be requested only by devices, controllers, and memories.
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 1/0
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 1/0 transfers) and/or report status.
device unit: One drive 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.
O_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 VAX/VMS
system. Contrast with monitor console routine.
direct data path: A UNIBUS adapter data path that transfers 16 bits of data in a
single SBI transfer.

Glossary-1 5

Glossary

direct 1/0: An 1/0 operation in which the system locks the pages containing the
associated buffer in physical memory for the duration of the 1/0 operation. The 1/0
transfer takes place directly from the process buffer. Contrast with system-buffered
1/0.
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.
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 file 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
to the receiver 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 to the original
owner 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.
displacement deferred mode: An address mode in which the specifier extension is
a byte, word, or longword displacement. The displac:ement 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.
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.

OMA: Direct memory access.

16-Glossary

Glossary

double floating data: A double precision floating point number eight bytes long
having a range of+/- 2.9•10-37 to+/- 1.7•1038 and a precision of approximately
sixteen decimal digits.
downline system load: A DECnet-VAX function that allows a remote target node to
receive an operating system file image from another node.
downline task load: A DECnet-VAX function that allows a remote target node to
receive an RSX-llS task from another node.
DPT: See driver prologue table.
drive: The electromechanical unit of a mass storage device system on which a recording
medium (disk cartridge, disk pack, or magnetic tape reel) is mounted.
driver: The set of code and tables that handles physical 1/0 to a device.
driver dispatch table (DDT): A table in the 1/0 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 at which a driver fork processes
executes, that is, IPLs 8 through 11. Every unit control block indicates the driver
fork level for its unit.
driver prologue table (DPT): A table in the driver that describes the driver and the
device type to the VAX/VMS procedure that loads drivers into the system.
driver start 1/0 routine: See start 1/0 routine.
DST: Debug symbol table.
DTE: See data terminal equipment.
DV: Decimal overflow trap enable bit in the processor status word.
dynamic access: A technique in which a program switches from one record access
mode to another while processing a file.
ECB: Exit control block.
EBCDIC: Extended Binary Coded Decimal Interchange Code; a set of 8-bit characters
used for representing data.
ECC: 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.
Glossary-17

Glossary

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 or restored on a
subroutine or procedure call using the call and return instructions.
entry point: A location that can be specified as the object of a call. It contains an entry
mask and exception enables known as the entry point mask.
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.
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.
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.
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 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: Executive Mode Stack Pointer.
ESR: Exception service routine.
evasive action: A responsive behavior by VAX/VMS to discourage breakin attempts
whenever they seem to be in progress. VAX/VMS has a set of criteria it uses to
detect the fact that breakin attempts may be underway. Typically, once VAX/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 (I/O
completion). Some other events include swapping, wake request, and page fault. (2)
A network or system-specific occurrence for which the logging component maintains
a record.
event class: A particular classification of events. Generally, this classification follows
the DNA architectural layers; some layers may contain more than one class. Class
also includes the identification of system-specific events.
18-Glossary

Glossary

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 0.
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.
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 basic control and monitoring functions of the
operating system.
executive mode: The second most privileged processor access mode (mode 1). The

record management services and many of the operating system's system service
procedures execute in executive mode.
executor node: The node at which an NCP command actually executes.
exit: An image rundown activity that occurs when image execution terminates either

normally or abnormally. Image rundown activities include deassigning 1/0 channels
and disassociating common event flag clusters. Any user- or system-specified exit
handlers are called.
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): An 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.
extension: The amount of space allocated at the end of a file each time a sequential

write exceeds the allocated length of the file.
Glossary-19

Glossary

extent: The contiguous area on a disk containing a file or a portion of a file. A"n extent

consists of one or more clusters.
F11 ACP: 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 an error status code
for which the process must test.
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 fault and
restarting the instruction will give correct results.
FCB: File control block.
FCS: File control system.

FOL: See file definition language.
FDT: Function decision table.
FDT routine: Driver routines called by the Queue 1/0 Request system service to

perform device-dependent preprocessing of an 1/0 request.
F_floating-point data: See floating (point) data.
FID: 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): An 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 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 VAX 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
given. There is at least one file header for every file on the disk.

20-Glossary

Glossary

file identifier (FID): A 6-byte value used to uniquely identify a file on a Files-11 disk
volume. The file number, file sequence number, and relative volume number are
contained in the file identifier.
file name: The field preceding a file type in a file specification that contains a 1through 39-character name for a file.
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 medium. The RMS file organizations are
sequential, relative, and indexed.
file section: A file section is 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 a mass storage medium. 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 to provide a physical accessing technique suitable for the way in
which the data in the file is processed.
fi"le 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 Oto 39-character type 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 VAX/VMS
operating systems. Refer also to Files-11 Structure Level 1 and Files-11 Structure
Level 2.
Files-11 Structure Level 1: The original Files-11 structure used by IAS, RSX-llM,
and RSX-llD for disk volumes. VAX/VMS supports structure level 1 to ensure
compatibility among systems.
Files-11 Structure Level 2: The second generation disk file structure supported by
VAX/VMS.
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 carnage control information.
fixed-length record format: A file format in which all records have the same length.

Glossary-21

Glossary

fixed line numbers: Numbers fixed to lines of text in a file. EDT maintains a record

of them during the editing sessions in which the files are used; they are copied to
the file when the editing session ends.
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.

flag:

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.
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. A driver awaiting the processor resource has its
fork block linked into the fork queue.
fork dispatcher: A VAX/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 driver fork queue until no processes remain in the queue for
that IPL.
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. VAX/VMS uses software interrupts
and fork processes to synchronize executive operations.
fork queue: A queue of driver fork blocks that is awaiting activation at a particular

interrupt priority level by the VAX/VMS fork dispatcher.
form feed: In EDT, the movement of the cursor position to the start of a new page;

one of the default word delimiters; the default page delimiter.
FP: See Frame Pointer.
FPO: First part (of an instruction) done.
frame: A unit, which is delimited by flags and includes a header, that is used by the

link level to exchange data packets as well as control and error information between
a DTE and a DCE on a packet switching data network.
Frame Pointer (FP): General register 13 (R13). By convention, it contains the base

address of the most recent call frame on the stack.

FU: Floating underflow trap enable bit in the processor status word.
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 I/O function code.
22-Glossary

Glossary

function decision table (FDT): A table in the driver that lists all valid function codes
for the device and lists the addresses of I/O preprocessing routines associated with
each valid function.
function modifier: See I/ 0 function modifier.
functionality: A computer industry term for what the hardware or software can do.
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, typical general
identifiers might be PAYROLL for all users allowed to run payroll applications,
RESERVATIONS for operators at the reservations desk, or CHEM224 for students in
the CHEMISTRY 224 class, and so forth.
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 and/ 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•103°8 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 and/ or group number of the UIC.
global symbol: (1) A symbol defined in a module 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 that is 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 will also put
global symbol tables into an image. For example, the linker appends a global
symbol table to executable images that are intended to run under the symbolic
debugger, and it appends a global symbol table to all shareable images.
gold key: The upper-left key on the terminal keypad, which enables alternate keypad
functions.

Glossary-23

Glossary

group: (1) A set of users who have special access privileges to each other's directories
and files within those directories (unless protected otherwise), as in the context
system/owner/group/world, where group refers to all members of a particular
owner's group. (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. When, during an interactive
session, the terminal appears to be going nowhere or doing nothing, 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 PC

•

The 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 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 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 with all of
its current status. 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.

24-Glossary

Glossary

high-level language: A language for specifying computing procedures or organization
of data within a digital computer. Higher-level languages are distinguished from
assembly and machine languages by the omission of machine specific details
required for direct execution on a given computer. These languages' frequently allow
direct expression of abstract concepts important to an area of computer applications.
Programs written in a higher-level language require a translation system (usually an
interpreter or a compiler) to have the desired effect on a given computer system.
highwater marking: A technique for discouraging disk scavenging. In the truest
sense, 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. VAX/VMS 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•104932 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 DECnet, a node that provides services for another node (for
example, the host node supplies program image files for a downline load). For
VAX PSI, a node that accesses a pactket switching data network by means of an
X.25 multihost connector node. (2) The node that makes a device available to other
nodes in the VAXcluster. A host node can be either a VAX that adds the device to
the MSCP-server database or an HSCSO.

I DB: See interrupt data block.
identifier: A notation that represents a user or group of users to the system. There
are three types of identifiers: UIC identifiers, system-defined identifiers, and general
identifiers.
image: An image consists of procedures and data bound together by the linker. There
are three types of images: executable, shareable, and system.
image activator: A set of system procedures that prepares an image for execution.
The image activator establishes the memory management data structures required
both to map the image's virtual pages to physical pages and to perform paging.
image exit: See exit.
image 1/0 segment: That portion of the control region that contains the RMS internal
file access blocks (IFAB) and 1/0 buffers for the image currently being executed by a
process.
image name: The name of the file in which an image is stored.
Glossary-25

Glossary

image privileges: The privileges assigned to an image when it is installed. See 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 PC is used as the register in
autoincrement mode addressing.
inbound connection: Logical link connection requests that a task receives.
increment: To add one quantity to another; 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. It is either the user's terminal, the
batch stream, or a command procedure.
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.
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.
26-Glossary

Glossary

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: 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 data 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 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 the 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 system-wide 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 system-wide 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 VAX/VMS system. Examples are the
driver dispatch table, driver prologue table, device data table, unit control block,
channel request block, I/O request packet, and interrupt data block.
1/0 driver: See driver.
1/0 function: An I/O operation interpreted by the operating system and typically
resulting in one or more physical IfO operations.

Glossary-27

Glossary

1/0 function code: A 6-bit value specified in a Queue I/O Request system service that

describes the particular I/O operation to be performed (for example, read, write,
rewind).
1/0 function modifier: A 10-bit value specified in a Queue I/O Request system ·service

that modifies an I/O function code (for example, read terminal input no echo).
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 I/O database that describes an individual

I/O request. The Queue I/O Request system service creates an I/O request packet
for each I/O request. VAX/VMS and the driver of the target device use information
in the I/O request packet to process the request.
1/0 rundown: An operating system function in which the system cleans up any I/O in

progress when an image exits.
1/0 space: The region of physical address space that contains the configuration

registers, and device control/status and data registers. These regions are not
physically contiguous.
1/0 status block (IOSB): A data structure associated with the Queue I/O Request

system service. This service optionally returns a status code, number of bytes
transferred, and device- and function-dependent information in an IOSB. An IOSB is
not returned from the service call, but filled in when the I/O request completes.
IPL: See interrupt priority level.
IRG: See interrecord gap.
IRP: See I/O request packet.
IS: See interrupt stack.
ISAM: Indexed sequential access method.
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.

28-Glossary

Glossary

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 EDT editing
session.
journaling: The recording of input during an EDT editing session.
K: A unit for measuring the size of memory or similar resources. K is short for kilo and

is used roughly to mean 1000, although K is equal to 210, or 1024.
kernel mode: The most privileged processor access mode (mode 0). The operating
system's most privileged services, such as I/O drivers and the pager, run in kernel
mode.
key: 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; VAX
RMS uses the key to build an index. See primary key, alternate key, and random

access by key value.
Relative files: The relative record number of each data record in a data file; VAX
RMS uses the relative record numbers to identify and access data records in a
relative file in random access mode. See relative record number.
In 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 command name, qualifier, or option. Many keywords must be typed in
full; others may be truncated according to the rules of DCL.
known component: The classification for one or more of the same 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: 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 HOR will 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.

LBN: Logical block number.
level 1 router: A node that can send and receive packets, and route packets from one
node to another, only within a single area.
Glossary-29

Glossary

level 2 router: A 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 command interpreter
evaluates and substitutes before it parses a command string. Lexical functions return
information about the current process (the 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: Moving the cursor position down one line; one of the default word
delimiters in EDT. In keypad character editing, a line feed deletes the characters
from the cursor position to the left word delimiter.
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"
will actually be 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 DTE/DCE interface is defined as operating in two-way simultaneous
asynchronous response mode (ARM) with the DTE and DCE containing a
primary and secondary function.

•

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

linker: A system program that creates an executable program, called an image,
from one or more object modules produced by a language compiler or assembler.
Programs must be linked before they can be executed.
linking: The resolution of external references between 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.
30-Glossary

Glossary

literal mode: An addressing mode in which the instruction operand is a constant
whose value is 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.
load device: The drive that holds the distribution media during software installation.
local disk: A disk drive in a CI environment that is independent of HSC control.
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: An RMS record access technique in which a program accesses records in
an RMS 1/0 buffer area to reduce overhead. See also move mode.
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 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: A logging sink that is to receive a machine-readable record of events for
later retrieval. The logging file is user defined.

Glossary-31

Glossary

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: A logging sink that is to receive a record of events in a form that
is comprehensible to system users. Typically, a logging console is a terminal or a
user-specified file.
logging monitor: A logging sink that is to receive a machine-readable record of
events for possible real-time decision making. Typically, the logging monitor is a
user-defined program.
logging out: Issuing the DCL command LOGOUT, which informs the operating
system that the user has finished using a particular terminal.
logical block number: 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 logical block number.
logical channel: A logical link between a DTE and its DCE. The physical
communications line between a DTE and DCE is divided into a set of logical
channels.
logical channel number (LCN): A unique reference number that identifies a logical
channel. A 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 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.

32-Glossary

Glossary

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 through 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.
macro: A statement that requests a language processor to generate a predefined set of
instructions.
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 OPCOM read from system-wide mailboxes.
main memory: See physical memory.
main text buffer: In EDT, the default text buffer for keyboard input and for input
files, and the source for output files.
manual record unlocking: A VAX 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 the retrieval information for a file that is 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.
MASSBUS adapter: See MBA
maximum visits: The maximum number of nodes through which a packet can be
routed before reaching its destination.
MBA: MASSBUS adapter. An interface device between the backplane interconnect and
the MASSBUS.
MBZ: Must be zero.

MCR: See monitor console routine.
member number: The second number or its alphanumeric equivalent in a user
identification code that uniquely identifies that code.

Glossary-33

Glossary

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 interconnect: The internal processor bus for the VAX-11/750.
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.
MFD: Master file directory.
MFPR: Move From Process Register instruction.
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 is 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 language interpreter in an RSX-11
system; also an optional command language interpreter in a VAX/VMS system.
mount a volume: (1) To logically associate a volume with the physical unit on which
it is loaded (an activity accomplished by system software at the request of an
operator). (2) To load or place a magnetic tape or disk pack on a drive and place the
drive on line (an activity accomplished by a system operator).
move mode: An RMS record 1/0 access technique in which a program accesses
records in its own working storage area. See also locate mode.
MTAACP: Magnetic tape ancillary control process.
MTPR: Move To Process Register instruction~
multiaccess channel: A medium (for example, Ethernet) on which many transmitters
contend for access.
multicast addressing: An 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 ~odes on an Ethernet
and used to send a message to all nodes in the group in a single transmission.
multinational character set: An 8-bit character set containing the set of international
alphanumeric characters, including characters with diacritical marks.
34-Glossary

Glossary

multipoint circuit: A circuit connecting two systems, with one of the systems (the

control station) controlling the circuit, and the other system serving as a tributary.
multiport memory: A memory unit that can be connected to multiple processors and

that can contain resources (for example, mailboxes, common event flag clusters, and
global sections) for use by processes running on different processors.
mutex: A semaphore that is 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 access to the region of code.
NAM: See name block.
name block (NAM): An RMS user data structure that contains supplementary

information used in parsing file specifications.
native image: An image whose instructions are executed in native mode.
native mode: The processor's primary execution mode in which 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: Network ancillary control process.
network: A collection of interconnected individual computer systems.
network connect block (NCB): For DECnet, 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.
For VAX 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 object: Any task with a nonzero object type, for example, those programs

such as FAL and NML that provide generic services across a network.
network status notifications: Notifications that provide 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 1/0
completion.
network task: A nontransparent task that is able to process multiple inbound

connection requests; that is, it has declared a network name or object number.
node: An individual computer system in a network that can communicate with other

computer systems in the network.
node address: The required, unique, numeric identification required of each node in

the network.

Glossary-35

Glossary

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, which 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: An end node.
NSP: Network services protocol.
null: (1) The character with the ASCII code 000. (2) An absence of information.
null process: A small system process that is the lowest priority process in the system

and takes one entire priority class. Its only function is to accumulate idle processor
time.
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 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.
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 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 displacemettt 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.
36-Glossary

Glossary

On-Disk Structure Level1 (ODS-1 ): See Files-11 Structure Level 1.
On-Disk Structure Level2 (ODS-2): See Files-11 Structure Level 2.
opcode: The pattern of bits within an instruction that specifies the operation to be
performed.
OPCOM: See operator communication manager.
open accounts: Accounts that do not require passwords.
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(s).
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.
operator: The person responsible for daily maintenance of the system at a particular
installation. The operator does such things as 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. OPCOM is always active.
operator's console: Any terminal identified as a terminal attended by a system
operator.
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: Program region page table.
P1: See control region.
P1 through PS: See parameter.
Glossary-37

Glossary

P1 BR: See Control Region Base Register.
P1 LR: See Control Region Length Register.
P1 PT: 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 the low-order four bits of
the highest addressed byte, which represents the sign. The packed decimal string is
specified by its lowest addressed location and the number of digits.
packet: A unit of data to be routed from a source node to a destination node; for

VAX PSI, the unit of data switched through a PDSN. Normally a user data field
accompanied by a header carrying destination and other information.
packet assembly/disassembly (PAD) facility: A device at a PDSN node 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.
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.
page fault cluster size: The number of pages read in 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 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).

38-Glossary

Glossary

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.
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 VAX/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. This system only pages
a process against itself. The operating system's pager does not read in a referenced
page if that page is on the free or modified list.
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 RMS.
passwords: Character strings 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.
paste buffer: The default text buffer for cut-and-paste operations.
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: Process Control Block Base Register.
peripheral devices: 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,
which is analogous to a leased line. Packets are routed directly by the network from
one DTE to the other.
Glossary-39

Glossary

per-process address space: See process address space.
PFN: See page frame number.
PFN mapping: See page frame number mapping.
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 30-bit 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 medium that links two nodes in a network. Contrast

with logical link.
physical memory: The memory modules connected to the SBI 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.
PIO: See process identification.

PME: Performance monitor enable bit in PCB.
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 PC.
primary key: The mandatory key within the data records of an indexed file; used by

VAX 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 user password requested

from the user. Systems may optionally require a secondary password, as well. As a
user password, this password must be the password that is associated with the user
name that is supplied with it.

40-Glossary

Glossary

primary processor: The main processor in a VAX-11/782. The primary processor

handles 1/0, scheduling, paging, and all other system management functions.
Contrast with attached 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: A rank assigned to a process to determine its precedence in obtaining system

resources.
private section: An image section of a process that is not shareable among processes.

See also global section.
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/ or 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 that 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 contex.,t: The hardware and software contexts of a process.
process control block (PCB): A data structure used to contain process context. The

hardware PCB contains the hardware context. The software PCB contains the
software context, which includes a pointer to the hardware PCB.
process header: A data structure that contains the hardware PCB, accounting and

quota information, process section table, working set list, and the page tables
defining the virtual layout of the process.
process header slots: That portion of the system address space in which the system

stores the process headers for the processes in the balance set. The number of
process header slots in the system determines the number of processes that can be
in the balance set at any one time.
process identification (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 RMS internal file access block for each open file, and the
1/0 buffers, including the command interpreter's command buffer and command
descriptors.
Glossary-41

Glossary

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.
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; affect any process in the system regardless of UIC; set process
swap mode; create permanent event flag clusters; create another process; create a
mailbox; perform direct 1/0 to a file-structured device; 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. Process 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.
processor status word (PSW): The low-order word of the processor status longword.
Processor status information includes the condition codes (carry, over.flow, 0,
negative), the arithmetic trap enable bits (integer over.flow, decimal over.flow,
.floating under.flow), 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.
42-Glossary

Glossary

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 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 symbol 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: A type of login that permits a user from a remote node to effectively login

to a local node, as if the user owned an account on the local node. However, the
user does not specify a password in the access control string. In some cases, the
remote user does own the account, but in other cases the remote user shares the
account with other users.
psect: See program section.
pseudo device: An entity treated as an 1/0 device by the user or system, although

it is not any particular physical device. A pseudo device is a forwarding address
through which actual physical devices can always be reached.
PSL: See processor status longword.
PSW: See processor status word.
PTE: See page table entry.

pure code: See reentrant code.
QIO: Queue 1/0 Request system service, which is the VAX/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 FDT routines.

Glossary-43

Glossary

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). Wh~n 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 integ~r is in the range 2~3 to
263

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[=0ption]. 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: n: A line of jobs to be processed, for example, a batch job queue or a printer

job queue. Processing occurs primarily in FIFO order, but does reflect the priority
of the process that submitted the job. See also state queue and system queue. v: To
make an entry in a list or table, perhaps using the INSQUE instruction.
queue priority: The priority assigned to a job placed in a spooler queue or a batch

queue.
quota: The total amount of a system resource, such as CPU time, that a job is allowed

to use in an accounting period, as specified by the system manager in the user
authorization file. See also limit.
RAB: See record access block.

random access: Refers to memory or mass-storage devices on which all information

is equally accessible. With random access, the next location from which data is to be
obtained is not dependent on the location of the last data obtained.
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's file address: The retrieval of a record by its unique

address, which is provided to the program by 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.
range specification: A means for defining a string of text in EDT.
reachable node: A node to which the local node has a usable communications path.

44-Glossary

Glossary

read: The act or capability of an image to accept data. For example, when a TYPE
command is issued, 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.
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 thusbe 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 RMS user control block allocated at either assembly or
run time to communicate with VAX 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 RMS for retrieving and storing records ~n
a file. Access is by one of four methods: sequential, random by key, random by
record's file address, and random by relative record number.
record access mode switching: Term applied to the switching from one type of
record access mode to another while processing a file.
record blocking: The technique of grouping multiple records into a single block. On
magnetic tape an IRG is placed after the block rather than after each record. This
technique reduces the number of 1/0 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 medium. 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
and/ 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. RMS allows programs
to issue GET and PUT requests at the record level (record 1/0) as well as read and
write blocks (block 1/0). VAX RMS is an integral part of the system software; its
procedures run in executive mode.
Glossary-45

Glossary

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 1/0 operation is the
device's physical record.
record's file address (RFA): The unique address of a record in a file that 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.
register deferred mode: An addressing mode in which the contents of the specified
register are used as the address of the actual instruction operand.
register mode: An addressing mode in which the contents of the specified register are
used as the actual instruction operand.
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; used as the key during random access
by key mode to relative files.
REMACP: Remote 1/0 ACP.
remote command terminal: A terminal that is logically connected to another node
by means of a network, in the way that a command is physically connected to a
node by means of a dialup line.
remote device: A device that is not directly connected to the local node, but is
available through the VAXcluster.
remote DTE: Any DTE in a network other than the one at which the user is located.
remote node: Any node in the network other than the one at which the user is
located. 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: 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.

46-Glossary

Glossary

resource wait mode: An execution state in which a process indicates that it will wait

until a system resource becomes available when it issues a service request requiring
a resource. 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 o(the VTlOO 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's 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.
RMS-11 : A set of routines that are linked with compatibility mode programs, and
provide similar functional capabilities to VAX RMS. The file organizations and
record formats used by RMS-11 are very similar to those of VAX RMS.
round robin: A form of time sharing that gives images of equal priority equal access to

the CPU. The VAX/VMS operating system uses round-robin scheduling for each of
the sixteen software priority levels. Each process at a given software priority level
executes in tum before any other process at that level (a FIFO queue).
router: A node that can send and receive packets, 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 in which 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: Relative volume number.
RWED: Read, Write, Execute, Delete.
SBI: See Synchronous Backplane Interconnect.
SBR: See System Base Register.

Glossary-4 7

Glossary

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.
SCB: See System Control Block.
SCBB: See System Control Block Base Register.

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
issued, new output appears at the bottom of the screen and eventually disappears
off the top.
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 file
locations 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 password more time consuming.
secondary storage: Random access mass storage.
secondary vector: A location that identifies the starting address of a condition handler
to be executed when a condition occurs and 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 VAX/VMS software designed to ensure that users
can only login 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 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.
48-Glossary

Glossary

sequential access mode: The retrieval or storage of records in which 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 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.
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 memory: See multiport memory.
shell process: A predefined process that the job initiator copies to create the minimum
context necessary to establish a process.
shrink 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 issue commands to the command
interpreter from a slave terminal.

SLR: See system length register.
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.
software context: The context maintained by the VAX/VMS operating system to
describe a process. See software process control block.
software interrupt: An interrupt generated on interrupt priority levels 1 through 15,
which can be requested only by software.
software priority: See process priority and queue priority.

Glossary-49

Glossary

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 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.
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 1/0 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.
SRP: Short request packet.
SSP: 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 LIFO concept. As items are added to
("pushed on" ) the stack, the 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 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 will access 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.
50-Glossary

Glossary

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, 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.
status: A display type for the 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 RO upon
completion.
store through: See write through.
stream: An access window to a file associated with a record access control block,
supporting record operation requests.
stream record format: Property of a file specifying that the data in the file is
interpreted as a continuous sequence of bytes, without control information. Stream
record format applies to sequential files only.
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 form a
command is often called a command string.
string search buffer: A buffer used to store the string 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: A subsidiary routine that executes when called by another program. A
subroutine is often called repeatedly until a. certain condition is met.
Glossary-51

Glossary

substate: An intermediate circuit state that is displayed for a circuit state display when

the NCP commands SHOW or LIST are issued.
substitute buffer: A buffer used to store the string to be substituted for the search

string.
summary: The default display type for the 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.
suspension: A state in which a process is inactive, but known to the system. A

· suspended process becomes active again only when another process requests the
operating system to resume it. Contrast with hibernation.
SVA: See system virtual address.
swap mode: A process execution state that determines the eligibility of a process to
be swapped out of the balance set. If process swap mode is disabled, the process

working set is locked in the balance set.
swapper: The process that performs 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

connected to a PDSN, 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 full process that transfers record-oriented data to or from a mass storage

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.
symbolic debugger: A program that aids a programmer in finding errors in other

programs.
52-Glossary

Glossary

Synchronous Backplane Interconnect (881): 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 I/O 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.
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, the 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-buffered 1/0: An 1/0 operation, such as terminal or mailbox 1/0, in which an

intermediate buffer from the system buffer pool is used instead of a process-specified
buffer. Contrast with direct 1/0.
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.
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.

Glossary-53

Glossary

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

in longwords.
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 PTE for each page of system region virtual memory. The physical base
address of the SPT is contained in a register called SBR.
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 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 SCB, the SPT, and process page tables.
system services: Procedures provided by the operating system that can be called by

user images.
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: In networking, refers to an image running in the context of a process.
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 and
VTlOO video display terminal.
text buffer: An EDT storage area for text (either terminal input or file input).
tied account: See captive account.
timeout: The expiration of the time limit in which a device is to complete an I/O

transfer. The driver's wait for interrupt request specifies the timeout limit.
54-Glossary

Glossary

timer: Two system processes, one that maintains the time of day and the date, and
another that scans for device timeouts and performs time-dependent scheduling
upon request. The timer interrupt service routine creates the timer process.
time sharing: A method of allocating computer time in which each process gets an
equal amount of time in tum. See also real-time processing.
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.
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.
transparent: The performance of functions that are not visible to the user. For
example, when a command is issued, 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.
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 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 m~in 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 in which 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.
Glossary-55

Glossary

UBA: UNIBUS adapter; an interface between the backplane interconnect to the VAX-11
/780 and the UNIBUS.
UBI: UNIBUS interconnect; an interface between the backplane interconnect to the
VAX-11/750 and the UNIBUS.
UCB: See unit control block.
UETP: See User Environment Test Package.

UFO: See directory.
UIC: See user identification code.
unblocked records: A record that is contained in a single block. No other records or
parts of records are contained in that block.
UNIBUS adapter: See UBA
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 fail 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 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 RSX-llS node to
dump its memory to a file on a VAX/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, serious errors,
and power fail.
user authorization file: 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, 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.

56-Glossary

Glossary

user file directory (UFO): See 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 name: The name that a user types on a terminal to log on to the system. See

also password.
user number: See member number.
user password: A password that is associated with a user. This password must be

correctly supplied when the user attempts to log in so that the user is authenticated
for access to the system. The two types of user passwords are primary and
secondary.
user privileges: The privileges granted a user by the system manager. See process

privileges.
USP: 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 Rl l, 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; 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 with fixed-length control 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/ or print format controls.

VAX/VMS: Virtual Address Extension/Virtual Memory System.
VBF: See variable-length bit field.
Glossary-5 7

Glossary

VCB: Volume control block.
vector: (1) An interrupt or exception vector is a storage location known to the
system 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
but for version number. (2) The number used to identify the revision level of
program.
video terminal: A terminal with a video screen for accepting output. See terminal.
virtual address: A 32-bit integer identifying a byte location in virtual address space.
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.
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 virtual address space seen by the programmer is a linear array of
4,294,967,296 (232) byte addresses.
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 connected to a PDSN 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/ directory for the console media. Also, because the command
procedure that handles the task invokes EXCHANGE, the conversion of the file
format from RTll 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.
58-Glossary

Glossary

volatile database: A memory image that contains information about network
management components.
volume: A mass storage medium such as a disk pack or reel of magnetic tape. The
volume is the largest logical unit of the file structure.
volume set: The file-structured collection of data residing on one or more mass storage
media.
VPN: See virtual page number.
wait: To become 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.
wake: To activate a hibernating process. A hibernating process can be awakened by a
time-scheduled wake-up call.
WCB: Window control block.
WCS: Writeable control store.
WDCS: 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 to search the default library's global symbol table to resolve the reference
if the definition is not in the modules explicitly supplied to the linker. Weak
references are often used when creating object modules to identify those global
symbols that may not be needed at run time.
wildcard character: A nonalphanumeric character such as an asterisk or percent sign
that is used within or in place of a file name, file type, directory name, or version
number in a file specification to indicate "all" for the given field.
window: (1) See mapping window. (2) A range of packets authorized for transmission
across an X.25 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).

Glossary-59

Glossary

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: A system process that brings process working sets into the
balance set and removes them from the balance set.
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.
write: The act or capability of an image to send data. For example, when a PRINT
command is issued, the specified file is read from wherever it is stored and 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 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.

XAB: See extended attribute block.
XDELTA: A tool for debugging operating systems and drivers.

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 and DCEs
for equipment operating in the packet mode on public data networks.
X.28: A CCITT recommendation that specifies the 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.

60-Glossary

Glossary

X.29: A CCITT recommendation that specifies procedures for the exchange of control
information and user data between a packet-mode DTE and a Packet Assembly
/Disassembly (PAD) facility.
X.29 terminal: A terminal connected to a Packet Assembly /Disassembly (PAD)
facility.

Glossary-61

VAX/VMS Glossary
AA-Z 102A-TE

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