.login
In UNIX-based operating systems: A C shell start-up file that executes when the user logs into the system. It contains commands and variables that affect the user environment.
.mailrc
In UNIX-based operating systems: A start-up file in the user's home directory that customizes the mailx program.
.nodes file
In UNIX-based operating systems: A file in the user's home directory which defines aliases for remote nodes on the user's network.
.profile
In UNIX-based operating systems: A Bourne and Korn shell start-up file that modifies the user environment. The user can add environment variables and commands to this file.
2-phase commit
In online transaction processing: The protocol used for global transactions in which each participating resource manager indicates a readiness to commit and then waits for the coordinating process to give permission to commit.
138.95 gateway
A gateway that provides access to the 138.95 network. It broadcasts to the outside world only the fact that it can route packets for the entire network, which external gateways can treat as a single entity. This simplifies the routing decisions that external gateways must make when attempting to reach an address on the 138.95 network: they simply send them to the 138.95 gateway. Upon receiving packets, the 138.95 gateway routes them to the appropriate subnet. See also subnetting.

A

A-Mode
See Asynchronous Mode (A-Mode).
ABI
See Application Binary Interface (ABI).
abort
  1. Cancel all operations associated with a transaction. Back out all changes to database contents.
  2. In UNIX-based operating systems: A function used by either the source or target task to immediately terminate the logical link.
abortive release
In networking: An abrupt termination of a transport connection, which may result in the loss of data.
access ACL
In DYNIX/ptx operating system: An ACL (access control list) that defines the permissions allowed for a particular file or directory. The operating system consults the ACL when a user attempts to access the file or directory. See also access control list (ACL).
access control
In UNIX-based operating systems: Information consisting of a username, password, and account string which is used to gain access for a client application to a server application. See also access control list (ACL).
access control entry (ACE)
In Windows NT operating system: An entry in an access control list (ACL) which is made up of a security ID (SID) and a set of access rights. See also access control list (ACL), access right, security ID.
access control field
In networking: The second byte of the token-ring three-byte packet. Grants network access to the packet.
access control list (ACL)
In DYNIX/ptx operating system: A list that specifies the users and groups allowed to access a particular file or directory.
In the Windows NT operating system: Part of a security descriptor that lists the protections applied to an object, whether it be a file, thread, event, or access token. An access control list is made up of access control entries (ACE). See also access control entry (ACE), access token.
access right
In Windows NT operating system: A permission granted to a process to manipulate a particular object in a particular way, by calling a service, for example. Different object types support different access rights, which are stored in the access control list (ACL) for each object. See also access control entry (ACE), access control list (ACL).
access token
In Windows NT operating system: An object that identifies a user who is logged in. An access token is attached to all the user's processes and contains the user's security ID (SID), the names of any groups to which the user belongs, any privileges the user owns, the default owner of objects created by user processes, and the default access control list (ACL). See also access control list (ACL), security ID (SID).
account
In UNIX-based operating systems: The login name and access privileges of a user.
ACE
See access control entry (ACE).
ACF
See Advanced Communications Function (ACF).
ACL
See access control list (ACL).
ACSE
See association control service element (ACSE).
active monitor
In ptx/CLUSTERS: The monitor that periodically checks all the other nodes of the cluster, controls online replacement (OLR) operations, and monitors the health of the cluster. See also cluster, online replacement (OLR).
active window
See focus window.
ACU
See Automatic Call Unit (ACU).
Ada
A programming language used extensively by the U.S. Department of Defense.
ADAM
See Advanced Detection Availability Manager.
ADAM Automation
Software that integrates the ADAM hardware devices into a single management system.
ADAM Console
A rack mountable flat panel display with keyboard and trackpoint that is used as the primary console for local access on the ADAM LAN. It is possible to use a Console Extender to connect an additional MVK Console to the ADAM LAN.
ADAM Hardware
The hardware sysbsystem used to establish connectivity to the management interfaces of the NUMACenter. ADAM hardware consists of the ADAM Enclosure, ADAM Ethernet Hub, Port Server, Modem Rack and modems, MVK Switch, rackmount PDU, and cabling.
ADAM LAN
A private management LAN dedicated to management and service applications within a NUMACenter. The ADAM LAN is hosted through the ADAM Ethernet Hub.
ADAM Server
An IBM Netfinity 5600 that serves as a dedicated host for support of management applications within the NUMACenter. The ADAM Server runs Netfinity Director and NUMACenter Director.
ADAM Software Stack
All software installed and configured on the ADAM Server.
address
  1. The means by which a host identifies a device.
  2. A network path used to route E-mail and news between machines.
  3. A numeric code, generated by the central processing unit, which designates a memory location or device. See also central processing unit (CPU).
address, device
See device address.
address mask
See netmask.
Address Resolution Protocol (ARP)
The TCP/IP protocol used to convert an IP address to a physical address. ARP is limited to networks that support hardware broadcasts.
addressing protocol
The correct way to address electronic mail for sending it across networks.
administrative logins
Special system login accounts that control specific directories or allow access to system functions. See also login account.
Administrative Management Domain (ADMD)
In X.400 networking: A public data network X.400 service, such as AT&T's ATTMAIL or Telenet's Telemail 400. See also Private Management Domain (PRMD), X.400.
Administrator's Runtime Kit (ARK)
In ptx/LICENSE: The run-time environment for licensed software products. It consists of the network license management daemon (netlsd) and its associated tools: ls_admin, ls_rpt, and ls_stat.
ADP
See automatic data processing (ADP).
Advanced Communications Function (ACF)
In SNA networking: IBM's official name for its line of SNA products. See also Systems Network Architecture (SNA).
Advanced Detection Availability Manager
The ADAM subsystem provides NUMACenter systems management. ADAM is composed of the ADAM Server, the ADAM hardware, the ADAM software stack, and the ADAM Console.
Advanced Program-to-Program Communications (APPC)
In SNA networking: An advanced SNA facility that supports synchronous (concurrent) program execution and program-to-program communications in a distributed environment. APPC is implemented with LU type 6.2 and PU type 2.1.
AE
See application entity (AE).
AFI
See Authority and Format Identifier (AFI).
agent
In ptx/AGENT: The local system running the manager process. Agent processes report their status to the manager process. See also manager.
AID character
See attention identifier (AID) character.
alias
In UNIX-based operating systems: A word equated to a list of login names or to a command. In the Korn and C shell programs, typing an alias causes the operating system to execute the command or commands defined by the alias. In the mailx program, mail sent to an alias goes to all users whose login names are defined by the alias.
allocate
To assign a resource to a specific task.
allocation unit
A group of consecutive blocks on a filesystem; the blocks contain resource summaries, free resource maps, data blocks, and a copy of the super-block.
alphanumeric
Pertaining to a character set that contains letters, digits, and usually other characters, such as punctuation marks.
ALU
See arithmetic logical unit (ALU).
American National Standards Institute (ANSI)
A private, nonprofit organization whose membership includes private companies, U.S. government agencies, and professional, technical, trade, labor, and consumer organizations. ANSI coordinates the development of voluntary consensus standards in the U.S.
American Standard Code for Information Exchange (ASCII)
A standard character set, consisting of 8-bit coded characters (7-bit code plus 1 parity bit), used for information interchange among data processing systems, data communication systems, and associated equipment. The ASCII set includes control characters and graphic characters.
anonymous login account
In the audit system, a login account that can be accessed by more than one user. The root login is an anonymous account. See also login account.
ANSI
See American National Standards Institute (ANSI).
AP
  1. See application process (AP).
  2. See application program (AP).
API
See application programming interface (API).
APPC
See Advanced Program-to-Program Communications (APPC).
applet
In the Microsoft Windows environment: An icon representing one feature or function of a program rather than the whole program.
Application Binary Interface (ABI)
In programming: A standard interface by which an application program gains access to system services such as the operating-system kernel. It is one step beyond the application programming interface (API), which defines the calls from the application to the operating system. The ABI defines the API plus the machine language for a particular central processing unit (CPU) family; therefore, unlike an API, the ABI ensures runtime compatibility between application programs and computer systems that comply with the standard. See also application programming interface (API).
application entity (AE)
In OSI networking: The OSI portion of an application process. See also Open Systems Interconnection (OSI) reference model.
application entity qualifier
In OSI networking: The identifier of an application process, among several in an application entity that share the same application process title. See also application entity (AE), Open Systems Interconnection (OSI) model.
application entity table (AE table)
In OSI networking: A table that maps network addresses to user-friendly names. See also Open Systems Interconnection (OSI) reference model.
application entity (AE) title
In OSI networking: The identifier of a particular application entity. See also application entity (AE), Open Systems Interconnection (OSI) model.
application layer
In OSI networking: The layer that provides functions and procedures used for managing communication between application processes. See also Open Systems Interconnection (OSI) model.
application port
In LAT networking architecture: A terminal device used to access remote LAT services.See also Local Area Transport (LAT).
application process (AP)
In OSI networking: A component within a real open system. An application process is an abstract representation of the elements of the open system that performs processing for an application. See also real open system, Open Systems Interconnection (OSI) model.
application process (AP) title
In OSI networking: The identifier for an application process. This and the application entity qualifier make up an application entity title. See also application entity (AE) title, application process (AP), Open Systems Interconnection (OSI) model.
application program (AP)
  1. A complete, self-contained program, such as an editor or electronic mail, that performs a specific task for the user, in contrast to system software, such as the operating system kernel, server processes, and program libraries.
  2. In network communications: A program used to connect and communicate with stations in a network, enabling users to perform application-oriented activities.
application programming interface (API)
A set of routines used by an application program to request low-level services from the operating system. See also application binary interface (ABI), application program (AP), operating system.
Application Region Manager (ASE)
In DYNIX/ptx, a feature that allows system resources such as CPUs, memory, and process table slots to be partitioned. This feature can be used to control the system workload.
application service element (ASE)
In OSI networking: A part of an application entity (AE) that provides a specific service to the application process (AP). See also application entity (AE), application process (AP), Open Systems Interconnection (OSI) model.
application-specific integrated circuit (ASIC)
In computer chip design: A integrated circuit created by first mounting an array of unconnected logic gates on a substrate and later connecting these gates in a particular configuration for a specific application. This design approach allows chips for a variety of applications to be made from the same generic gate array, thereby reducing production costs.
arbitrated loop
A Fibre-Channel topology that provides a low-cost solution to attach multiple communicating ports in a loop.
arbitration
The process of managing competing demands from multiple processes or users for a system resource.
architecture
  1. A set of rules for the design of a network.
  2. A synonym for topology.
  3. An overview of the relationship among the hardware or software components of a computer system.
archive
See back up, backup.
argument
  1. A value passed between programs or functions that specifies how, or upon what, they are to operate.
  2. An element of a command line that specifies the data on which a command is to operate (such as the name of a file or directory). For example, in the command lp -d<printer>, lp is the command, -d is an option that tells lp to send the output to a specific printer, and <printer> is an argument that specifies the printer. Also called "parameter."
arithmetic logical unit (ALU)
The part of the central processing unit (CPU) that performs arithmetic, comparative, and logical functions.
ARK
See Administrator's Runtime Kit.
ARP
See Address Resolution Protocol (ARP).
ARPANET
The network that grew out of networking research funded by DARPA (formerly ARPA). Serving from 1969 to 1990, ARPANET was replaced by Internet. The ARPANET used the TCP/IP protocol suite.
array
An indexed group of data elements, all of the same type. Each element can be referenced individually by identifying the array and using the appropriate indexing expression, or the entire array can be manipulated as a unit.
ASCII
See American Standard Code for Information Interchange (ASCII).
ASE
See application service element (ASE).
association
In ptx/SVM: The logical relationship between a subdisk and a plex or between a plex and a volume. See also plex, volume.
association control service element (ACSE)
In OSI networking: The application service element (ASE) responsible for establishing and releasing associations (presentation-layer connections). See also application service element (ASE), Open Systems Interconnection (OSI) model.
asynchronous
Describing a process which takes place with no timing signals. Devices such as terminals and serial printers operate asynchronously.
asynchronous execution
The mode of execution in which Transport-Interface routines never block while waiting for specific asynchronous events to occur, but instead return immediately if the event is not pending.
asynchronous interface
RS-232-style interface used for terminal and low-speed computer communication.
Asynchronous Mode (A-Mode)
Under Construction.
Asynchronous Tranfer Mode (ATM)
In OSI networking: International standard in which multiple service types (such as voice, video, or data) are conveyed in fixed-length (53-byte) cells. Fixed-length cells allow processing to occur in hardware and thereby reducing transit delays. ATM is designed to take advantage of high-speed transmission media such as E3, T3, and SONET.
asynchronous transmission
In networking: Transmitting digital signals without precise clocking. Such signals generally have different frequencies and phase relationships. Asynchronous transmissions usually encapsulate individual characters in control bits (called start and stop bits) that designate the beginning and end of each character.
asynchronous write
A delayed write, in which the data is put into a page in the system's page cache, but is not written to disk before the write returns to the caller. This improves performance but risks data loss if the system crashes before the data is flushed to disk.
ATM
See Asynchronous Transfer Mode.
ATM Adaptation Layer (AAL)
In OSI networking: A service-dependent sublayer of the data-link layer. The AAL accepts data from different applications and presents it to the ATM layer in the form of 48-byte ATM payload segments. AALs consist of two sublayers, CS and SAR. AALs differ on the basis of the source-destination timing used, whether they use variable bit rate or constant bit rate, and whether they are used for connection-oriented or connectionless mode data transfer.At present, the four types of AAL recommended by the ITU-T are AAL2, AAL3/4, and AAL5.
ATM adaptation layer 5 (AAL5)
One of four AALs recommended by the ITU-T standard. AAL5 supports connection-oriented, variable-bit-rate services and is used predominantly for transporting classical IP over ATM and LANE traffic. AAL5 uses "simple and efficient AAL" (SEAL) and is the least complex of the current AAL recommendations. It offers low bandwidth overhead and simpler processing requirements in exchange for reduced bandwidth capacity and error-recovery capability.
ATM layer
Service-independent sublayer of the data-link layer in an ATM network. The ATM layer receives the 48-byte user-data segments from the AAL and attaches to each a 5-byte header, producing standard 53-byte ATM cells. These cells are passed to the physical layer for transmission across the physical medium. See also AAL.
ATMI
See Application Transaction Manager Interface (ATMI).
atomic copy
In the ptx/SVM: A special type of I/O done by some of the ptx/SVM utilities, such as volplex att, during plex resynchronization. The entire I/O is done as a single operation; other writes cannot intervene during this operation.
attach service
In ptx/LAN: Assigns a physical point of attachment (PPA) to a stream.
attention identifier (AID) character
A nondisplayable character which is sent when an operator takes an action (such as using a selector pen or pressing a program function [PF] key) and which produces a data-entry signal. The character identifies the action or key that generates the condition and is available to programs that use full-screen processing.
attention key
A terminal function key for generating an I/O interrupt in the central processing unit (CPU). See also interrupt, central processing unit (CPU).
attribute fileset
In ptx/EFS: A special fileset that stores the structural elements of the filesystem. These structural files are the "property" of the filesystem and are not normally visible to the user.
audit class
In the auditing features of DYNIX/ptx operating systems: A set of related events that are audited in the same manner. For example, the link class includes the link and unlinksystem calls.
audit mask
In the auditing features of DYNIX/ptx operating systems: A set of audit classes that are audited for particular users.
audit trail
In the auditing features of DYNIX/ptx operating systems: A record of the events that were audited on the system.
authentication ID
In the auditing features of DYNIX/ptx operating systems: An ID assigned to each operating-system process. The audit system uses the ID to associate the process with the user who executed it.
Authority and Format Identifier (AFI)
Under Construction.
autoconfiguration
In DYNIX/ptx operating system: A process that takes place when the system is booted. The process locates each device on the system and assigns a name to it.
automatic backup
In UNIX-based operating systems: A backup, typically started by the cron command, that occurs at a predefined time. See also cron command.
automatic data processing (ADP)
Under Construction.
automatic call unit (ACU)
A hardware device that can dial telephone numbers; it is usually built into a modem. The UUCP system uses automatic call units to contact a remote system over telephone lines.
automatic logon
A process by which ACF/VTAM creates a session-initiation request (logon) for a session between a secondary logical unit and a designated primary logical unit. In order for this request to be created, the secondary logical unit cannot be a secondary application program and cannot be in session with, or queued for a session with, another primary logical unit. See also logical unit (LU), Systems Network Architecture (SNA).
autopush
The action performed by the kernel STREAMS subsystem on the first open of a STREAMS device (such as the system console), whenever a STREAMS module is pushed (by the I_PUSH ioctl) on a STREAMS stack.
autowrap
A feature of a character display: the cursor automatically returns to the beginning of the next line when output would otherwise extend beyond the right edge of the screen.

B

back-enable
In network programming for UNIX-based systems: To schedule a previously blocked queue for processing when the STREAMS scheduler determines that a succeeding queue has reached its low-water mark.
background
In UNIX-based operating systems: A mode for executing commands. When you run a command in the background, the shell does not wait until the command is completed. Instead, it displays the command prompt, allowing you to enter another command.
background window
See root window.
back out
To reverse all effects of a data transaction upon a database.
backplane
A device containing slots and sockets to accept boards.
back up
To copy information such as a file, directory, or filesystem for safekeeping (typically on removable magnetic tape).
backup
  1. The process of making a copy of a file, directory, or filesystem as insurance against data loss or corruption. If you back up a directory or filesystem, the backup procedure preserves the directory structure. See also back up.
  2. An archived copy of backed-up data. See also back up.
backup copy
A copy of a file or data set that is kept for reference in case the original file or data set is destroyed or needed again.
backup cycle
The frequency with which full and incremental backups are performed. Typical backup cycles are one week and one month.
backup device
A data-storage device used for saving and recovering data.
backup log
A file containing a record of backup activity, created automatically as part of the backup process.
bandwidth
The range of frequencies an electronic system can transmit or receive. The greater the bandwidth of a system, the more information the system can transfer in a given period of time.
baseband
The frequency band occupied by information signals before they are combined with a carrier in the modulation process.
baseband transmission
A transmission mode in which a base voltage on the transmission medium is varied to indicate one and zeros.
BASIC (Beginner's All-purpose Symbolic Instruction Code)
A high-level programming language.
Basic Telecommunications Access Method (BTAM)
The basic access method for IBM 3270 data communications.
batch
  1. An accumulation of data to be processed.
  2. A group of records or data-processing jobs brought together for processing or transmission.
  3. A processing mode in which jobs are submitted for processing without human intervention.
batch queue
A queue that places batch jobs in sequence for execution. A batch queue's run limit controls how many jobs in the queue can run simultaneously.
batch queue complex
A named set of batch queues considered as a single entity so that one run limit can be applied to all. See also batch queue.
batch system
A system that processes data in discrete groups of previously scheduled operations, rather than interactively or in real time.
batch system configuration
All the nodes on which the batch system will run. The batch system has been "configured" for use on these nodes. See also batch system.
baud
The encoded bit rate per second.
baud rate
The speed, measured in number of signal changes per second, at which serial data is transmitted through a modem.
BCD
See Binary-Coded Decimal (BCD).
BCS
See Binary Compatibility Specification (BCS).
BDF
See Bitmap Distribution Format (BDF).
beacon
In token-ring networking: A specialized data packet sent by a token-ring device to signal to all stations that the ring is broken.
Berkeley Internet Name Domain (BIND)
A distributed database for TCP/IP domain name systems developed by the University of California at Berkeley. also Domain Name System (DNS).
Berkeley Software Distribution (BSD)
In UNIX-based operating systems: The implementation of UNIX developed at the University of California at Berkeley, featuring network support, peripheral support, and an extensive software development environment, all of which helped UNIX gain commercial acceptance.
BIC
See Bus Interrupt Controller (BIC).
Binary-Coded Decimal (BCD)
A system for encoding decimal numbers in binary form to avoid rounding and conversion errors. In BCD, the digits of a decimal number are individually represented in 4-bit binary notation. For example, the decimal number 1024 is recorded in BCD as 0001000000100100.
Binary Compatibility Specification (BCS)
The Application Binary Interface (ABI) of 88open, a consortium for creating an open computing environment based on Motorola 88000 RISC processors. See also Application Binary Interface (ABI).
binary notation
The mathematical system based on powers of two, rather than powers of ten as in the decimal system. See also bit.
Binary Synchronous Communications (BSC)
A half-duplex, character-oriented, synchronous communication protocol developed by IBM. BSC transmits binary-coded data over a link connection. Also called "bisync." See also half-duplex.
BIND
  1. In SNA networking: A request to activate a session between two logical units (LUs). See also BIND type, logical unit (LU).
  2. See Berkeley Internet Name Domain (BIND).
bind service
In ptx/LAN: The service that associates a data-link service access point (DLSAP) with a stream.
BIND type
In SNA networking: A type field that specifies whether the BIND is negotiable or nonnegotiable. If negotiable, the secondary logical unit (LU) can, when a session is activated, determine whether it is able to support the BIND request and, if not, respond with an alternate version of BIND parameters. If nonnegotiable, the secondary LU may determine that it is unable to support the BIND request and, in that case, refuses to activate the session. See also BIND, logical unit (LU).
bisync
See Binary Synchronous Communications (BSC).
bit (binary digit)
  1. A single-digit binary number.
  2. The smallest unit of computer data, deriving from the transistors that make up computer memory. A single memory location can take the value 0 or 1, indicating that the corresponding transistor is off or on. All data in a computer system is represented in terms of binary numbers based on this principle.
bit map
  1. A rectangular area on the display composed of pixels, each of which is white, black, or, in color displays, a color.
  2. In the X Window System environment: The bit-map application program makes it possible to edit bit maps interactively; the resulting bit maps can be used as pointers, icons, and the root-window shade pattern. See also pixel.
Bitmap Distribution Format (BDF)
In the X Window System environment: The default format in which font files, with extension .bdf, are distributed. BDF files are then converted, by compiler, to the final format that is suitable for the destination server.
bit rate
The speed (usually in bits per second) at which data is transmitted over a TTY line (port).
bits per inch (bpi)
The density, measured in number of bits per inch, at which information can be stored on magnetic tape.
bits per second (bps)
The speed, measured in number of bits per second, at which data can be transmitted by serial equipment such as terminals, modems, printers, communication ports. Distinct from baud rate. See also baud rate.
blkno
See block number (blkno).
block
A collection of consecutive bytes of data read from or written to a block device, as a unit . A filesystem block typically contains either 4096 or 8192 bytes. See also block device, block number (blkno).
block device
A device that handles data in blocks. When the operating system needs to read or write data from a block device, it transfers blocks of data (in 2-KB units) to or from a buffer. Disk drives, for example, are block devices.
block number (blkno)
The address of a block of data on a disk.
blocked queue
A queue that cannot be enabled because of flow control.
Bluebook Ethernet
A standard for Carrier-Sense Multiple Access with Collision Detection (CSMA/CD), developed by the United States Department of Defense (DOD).
board
A flat board capable of holding processors, memory chips, and other electronic components. Also called "circuit board."
boot
To start a computer operating system.
boot block
The first 8-KB block on a disk. This block can contain programs for booting the operating system. Each filesystem also contains a boot block. See also block.
boot flags
Special bits that control the behavior of the operating system during the boot process.
bootname
The path to the kernel that will be booted.
BOOTP
See BOOTstrap Protocol.
BOOTstrap Protocol (BOOTP)
In TCP/IP networking: An alternative protocol by which a diskless machine can obtain its IP address and such configuration information as IP addresses of various servers from a BOOTP server. See also Reverse Address Resolution Protocol (RARP).
boundary function
In ptx/SNA: The capability of a subarea node to provide protocol support for adjacent peripheral nodes, such as transforming network to local addresses or local to network addresses; performing session sequence numbering for low-function peripheral nodes; and providing session-level pacing support.
bpi
See bits per inch (bpi).
bps
See bits per second (bps).
bracket
In SNA networking: One or more chains of request units (RUs) and their responses, exchanged between two logical-unit (LU) half-sessions and representing a transaction between them. A bracket must be completed before another bracket can be started. See also logical unit (LU), request/response unit (RU), and Systems Network Architecture (SNA).
Branch Predictor
The section of the Intel Pentium microprocessor that determines which of two data paths on the central processing unit (CPU) can most efficiently execute an operation stored in the code cache. See also central processing unit .
breakout cable
A cable with multiple connectors on one end and a single connector on the other end. Used to connect a single source or target with many sources or targets.
bridge
  1. In packet-switching networks: A system connecting two or more systems or networks and forwarding packets among them, using their physical addresses.
  2. In OSI networking: A device that forwards data frames from one LAN to another at the Data Link Layer. See also local-area network (LAN), Open Systems Interconnection (OSI) model.
  3. In Fibre Channel technology: A device that translates from one bus protocol to another bus protocol. The `Fibre Channel Bridge translates between the Fibre Channel protocol and the SCSI-2 bus protocol. See also Fibre Channel.
bridge process
In networking: A process that provides a network interface by maintaining virtual circuits to other nodes, so that application messages can be exchanged between nodes.
British Standards Institute (BSI)
An organization, founded in 1901, to approve standards for a wide variety of products in the U.K., with a view to establishing minimum standards of quality and avoiding duplication in design, size, and other attributes.
British thermal unit (Btu)
The amount of heat required to raise a pound of water by 1 degree Centigrade.
broadband
Describing a channel with a bandwidth of 10,000 to 50,000 bits per second (bps); also called "wideband." also bits per second (bps).
Broadband Integrated Services Digital Network (BISDN)
Communication standard developed by the ITU-T to handle high-bandwidth applications such as video. Uses Asynchronous Transmission Mode (ATM) technology over SONET-based transmission circuits. See also Synchronous Optical Network (SONET).
broadband transmission
A transmission mode in which the amplitude, frequency, or phase of an oscillating carrier signal is varied to indicate ones and zeros.
broadcast address
A group address indicating that all stations on one network will receive and process a transmitted message.
BSC
See Binary Synchronous Communications (BSC).
BSD
See Berkeley Software Distribution (BSD).
BSI
See British Standards Institute (BSI).
BTAM
See Basic Telecommunication Access Method (BTAM).
Btu
See British thermal unit (Btu).
buffer
  1. (n) A storage area in a computer's memory, temporarily reserved for use in performing an input or output operation. A buffer is typically assigned to a specific device, allowing the computer to continue operating while the slower device uses the data stored in the buffer. A buffer also allows the computer to receive data without stopping to process it immediately.
  2. (v) To use a buffer for the transfer of data. See also queue.
burst transfer
A type of data transmission in which a single device takes control of a bus or multiplexed channel. Central processing units (CPUs) and memory controllers make burst transfers when they read or write 8-, 16-, or 32-byte data blocks. These operations are called "burst" or "block" transfers, because multiple data cycles are associated with a single address cycle.
bus
  1. An electronic circuit used to transfer information among computer components and devices.
  2. In LAN networking: A type of layout for a LAN transmission medium consisting of a single data path that does not form a loop. Each station on a bus communicates directly with all other stations on the bus. See also local-area network (LAN).
Bus Interrupt Controller (BIC)
An integrated circuit used in the System Services Module (SSM). The BIC participates in the Symmetry bus protocol and controls the operation of the Peripheral Interface Controllers (PICs). See also Peripheral Interface Controller (PIC).
bus topology
In ptx/LAN: An arrangement in which each station on the bus is connected directly to every other station on the bus by a single data path that does not form a loop.
byte
An 8-bit unit of information.

C

C
A programming language designed by Bell Labs in 1972 for use as the systems language for the UNIX operating system.
C shell
A shell program (/bin/csh) that provides features such as job control and command history.
C++
An enhancement of the C language that adds features supporting object-oriented programming.
cabinet
The chassis in which the computer's components reside.
cache
A special section of memory used to store information temporarily for faster access. See also copyback cache, write-through cache.
cache coherence
Under Construction.
Cache-Coherent Nonuniform Memory Access/Architecture (CC-NUMA)
A variation of the NUMA architecture in which cache coherence is performed in hardware, not software. See also cache coherence, nonuniform memory access (NUMA).
cache miss
An event that arises when the central processing unit tries to read data that is not in its cache memory. When a cache miss occurs, extra time is required for the data to be retrieved from the main system memory and loaded into the cache. See also central processing unit (CPU).
CAD
See computer-aided design (CAD).
CADM
See Clock/Arbitration/Data-Mover (CADM).
CADM-2
See Clock/Arbitration/Display-Mover-2 (CADM-2).
CAE
See computer-aided engineering (CAE).
called DLS user
In OSI networking: The Data Link Service (DLS) user in connection mode that processes requests for connections from other DLS users. See also Data Link Service (DLS), Open System Interconnection (OSI) model.
calling DLS user
In OSI networking: The Data Link Service (DLS) user in connection mode that establishes a data link connection. See also Data Link Service (DLS), Open Systems Interconnection (OSI) model.
canonical format
In OSI networking: The chosen bit order within each byte whereby the Data Link Provider Interface (DLPI) presents addresses of the Data Link Service access point (DLSAP). The Data Link Service (DLS) user does not need to know the order of bit transmission on the physical media to use the DLPI interface. See also Data Link Provider Interface (DLPI), Data Link Service (DLS), Data Link Service access point (DLSAP), Open Systems Interconnection (OSI) model.
canonical processing
In UNIX-based networking: The processing of raw character data from a TTY driver, performing operations indicated by characters such as erase and kill and collecting the characters into lines (based on new-line characters). In a STREAMS-based TTY implementation, the driver normally handles the raw-device interface, and the canonical processing is performed by a module pushed between the driver and the stream head. The advantage to this modular approach is that one can change the raw driver for a different hardware or a network line and push the same canonical-processing module between the new driver and the stream head. This ensures that the canonical-processing procedure needs to be implemented only once and that the user sees the expected behavior.
CAQ
A small expansion cabinet for the S16, S2000/2x0, and S2000/4x0 systems.
carriage return-line feed (CRLF)
A two-character command sequence that moves the cursor to the left side of the screen and down one line.
Carrier Sense Multiple Access with Collision Detection (CSMA/CD)
A medium access method in which a station listens to the medium to determine if another station is currently transmitting a message. The CSMA/CD method also detects the resulting collision when two stations transmit simultaneously. Ethernet, for example, is a well-known network based on CSMA/CD technology.
cathode-ray tube (CRT)
A display device in which controlled electron beams are used to display alphanumeric or graphical data on an electroluminescent screen.
CAX-2000
A large expansion cabinet for S2000/7x0 systems, powered by single-phase AC.
CBT
A large expansion cabinet for S16, S2000/2x0, and S2000/4x0 systems, powered by single-phase AC.
CCA
See Conceptual Communications Area (CCA).
CCI
See Cluster Communications Interconnect.
CCITT (Comite' Consultatif International des Te'le'graphie et Te'le'phonie) International Telegraph and Telephone Consultative Committee
An international organization that defines standards for data communication; since March 1993, called the International Telecommunications Union Standardization Sector (ITU)-T.
cell
  1. In ptx/ATM: The basic unit for Asynchronous Transfer Mode (ATM) switching and multiplexing. Each cell consists of a 5-byte header and 48 bytes of user data (also called payload. Cells contain identifiers that specify the data stream to which they belong.
  2. In ptx/LICENSE: A subset of a network or internet in which all hosts use the same universal unique identifier (UUID) for the Global Location Broker object. Cells have independent GLB databases. For client hosts in cells that do not use the default GLB object UUID, the configuration file gib_obj.txt specifies an alternate UUID.
central processing unit (CPU)
The part of a computer where arithmetic and logical operations are performed and where instructions are decoded and executed. A microprocessor is an integrated circuit that contains a complete CPU.
Central Services Module (CSM)
A circuit board used in the S5000 system card cages. The CSM provides these systems with initialization, system-bus services, power-supply monitoring, and an interface with the front panel. The CSM includes two fast-wide differential SCSI buses and two serial ports.
chain
In SNA networking: A set of related request/response units (RUs) consecutively transmitted on a normal or expedited data flow. The request RU chain is the unit of recovery; if one of the RUs in the chain cannot be processed, the entire chain must be discarded. See also request/response unit (RU) .
change number of sessions (CNOS)
Under Construction.
channel
In Fibre Channel networking: A point-to-point physical link to transport data from one point to another. See also link.
character device
A device that handles data one character at a time, as a stream of bytes; for example, terminals, printers, and modems are character devices.
characters per inch (cpi)
The number of characters of a particular size and font that can fit into a line 1 inch long.
child directory
See subdirectory.
CIA
See classical IP over ATM.
CICS
See Customer Information Control System (CICS).
circuit
A connection that operates over a physical line to transport information between adjacent nodes.
class
  1. See audit class.
  2. See client class.
  3. See printer class.
class-1 laser component assembly
A device that produces and controls optical radiation while meeting the safety standard of non-harmful emission levels under all circumstances. See also Gigabaud Link Module, Gigabit Interface Converter, and Gigabit Optical Transceiver, .
classical IP over ATM (CIA)
In ptx/ATM networking: Specification for running the Internet Protocol (IP) over ATM in a manner that takes full advantage of the features of ATM. Defined in RFC 1577.
class name
In the X Window System: The name of a class of resources, widgets, or clients. Resource and widget class names are typically defined in the programming libraries used to create the client. See also client, resource, widget.
CLI
See Command Line Interpreter (CLI).
client
  1. The requesting program in a system in which a program at one site sends a request to a program (the server) at another site.
  2. A process that initiates requests for service. The term client describes the role a process plays in an OLTP system. Typically a user-interface process functions as a client while database services are handled by processes called ''server processes.'' However, a server process may at times assume the role of client; that is, servers may request services from each other. See also server.
  3. In the X Window System: An application program that communicates with the display server in the X protocol; it does not need to run on the same machine as the display server program. Examples of clients include xterm, xclock, and mwm. Also called "client applications" or "client programs."
  4. The transport user in connection-mode that initiates the establishment of a transport connection.
client class
In the X Window System: A collection of clients that shares a similar purpose and may also function similarly. For example, the client class WM is the collection of all window manager clients.
client instance
In the X Window System: An example of a client invocation or individual client from a client class. For example, such window manager clients as mwm, uwm, and twm are all client instances from the client class WM.
CLNP/CLNS
See Connectionless Network Protocol (CLNP)/Connectionless Network Service (CLNS).
Clock/Arbitration/Data-Mover (CADM)
A circuit board used in Symmetry 2000/700 and S81 systems. The primary functions of the CADM include generating clock impulses for timing data on the Symmetry system bus, controlling arbitration and priorities for all boards on the system bus, and controlling high-speed memory-to-memory transfers. The CADM also monitors memory and I/O for time-out conditions, generates the reference voltage for the termination block on the system backplane, and alerts the system operator (through the DC-OK indicator on the system front panel) when voltage is out of range.
Clock/Arbitration/Display-Mover-2 (CADM-2)
An updated version of the CADM board used in the Symmetry 2000/750 and 2000/790 systems. The CADM-2 performs all the functions of the CADM board except memory-to-memory transfers, which are handled by the SSM-2 board.
clock cycle
  1. The smallest unit of time recognized by the central processing unit (CPU)--typically a few hundred-millionths of a second.
  2. The time required for the central processing unit (CPU) to perform the simplest instruction, such as fetching the contents of a register or performing a NOP (no-op, an instruction that does nothing).
Also called "CPU cycle" or "clock tick." See also central processing unit (CPU).
clocking
In binary synchronous communications (BSC): The use of clock pulses to control the timing of data and control characters.
clock rate
The rate at which the clock in an electronic device, such as a computer, oscillates; typically given in hertz (Hz, one cycle per second), kilohertz (KHz, one thousand cycles per second), or megahertz (MHz, one million cycles per second). Also called ''clock speed.''
clone device
In UNIX-based networking: A STREAMS device driver that does not require that a particular minor device be opened; instead, the clone device allocates an unused minor device and opens it.
closed subroutine
In software programming: A program module that is copied once and can then be called or jumped to from any point in the program. See also open subroutine.
close procedure
  1. The routine that is called when a module is popped from a stream.
  2. The driver routine that is called when a driver is closed.
CLTP
See Connectionless Transport Protocol (CLTP).
cluster
  1. A type of distributed computing in which two or more computer systems share disk or tape resources over a common bus. Each individual computer, or node, in the cluster also has its own private resources.
  2. Two or more interconnected machines, each having its own copy of the operating system and sharing mass storage resources.
Cluster Communications Interconnect
In ptx/CLUSTERS: A dedicated local area network that carries Integrity Manager and Lock Manager traffic between cluster nodes. See also Integrity Manager, Lock Manager.
cluster controller
In SNA networking: A computer that controls communications among terminals or other devices and permits communication with a host computer. The cluster controller is connected to terminal-interface software that communicates over a network with host-interface software. Also called "control unit."
cluster membership
In ptx/CLUSTERS: A list of all members or potential members of a cluster.
CMS
See Conversational Monitor System (CMS).
CNOS
See change number of sessions (CNOS).
coaxial cable
A transmission medium in which a center conductor is surrounded by an insulating material. A metal braid that surrounds the insulating material acts as a second conductor.
COBOL (Common Business-Oriented Language)
A high-level, verbose programming language developed in 1961 and popular during the following two decades for business applications.
command
In UNIX-based operating systems: The name of a file containing a program or shell script. The command is issued when the name of the file is typed, which causes the operating system to execute the program or script in that file.
command interpreter
A program that reads commands and changes them into computer instructions. The UNIX Bourne shell, for example, is a command interpreter.
command line
A command typed at the shell prompt (usually $ or %). A command line can contain options and arguments, and it must end with <Return>.
Command Line Interpreter (CLI)
Under Construction.
command mode
A mode used by the ed and vi editors and the mailx program. When ed or vi is in command mode, commands move the cursor or edit text. When mailx is in command mode, mail is available to be read and responded to.
command substitution
In UNIX-based operating systems: A shell feature that makes it possible to use the output from one command as an argument to another command.
Command Terminal (CTERM)
Digital Equipment Corporation's Network Command Terminal protocol.
commit
To complete a database transaction so that changes to the database are recorded and stable.
Common Part Convergence Sublayer (CPCS)
Under Construction
communication controller
See front-end processor (FEP).
communication endpoint
In networking: The local communication channel between a Data Link Service (DLS) user and Data Link Service (DLS) provider. See also Data Link Service (DLS) user, Data Link Service (DLS) provider.
communications domain
A collection of related nodes within a network. The nodes may be subnetwork clients and servers under the control of the same security database, as in some local area networks; they may also be a collection of network addresses all related to the same topic area, as are Internet domains.
communications protocol
In networking: A set of standards defining how computers are to exchange information. See also Open Systems Interconnection (OSI) model, Systems Network Architecture (SNA) functional layers.
compaction
In SNA networking: The transformation of data by packing two characters into a byte so as to take advantage of the fact that only a subset of the allowable 256 characters is used; the most frequently sent characters are compacted. See also compaction table, compression, Systems Network Architecture (SNA).
compaction table
In SNA networking: A table used by sending an LU-to-LU (logical unit-to-logical unit) half-session to transform data so that fewer bytes are sent to the receiving half-session. The receiving LU-to-LU half-session uses the same table to reverse the process, thereby restoring the data to its original form. See also compaction, compression, logical unit (LU), Systems Network Architecture (SNA).
compiler
Software that accepts human-readable, high-level language source code as input and produces machine-readable, low-level executable code.
complex
See batch queue complex.
compound password
In ptx/LICENSE: A type of product password that specifies parameters for creating license passwords. In an end-user environment, a compound password can specify multiple nodelocked licenses. The compound password is installed at a license server, and the license server then derives license passwords (each of which specifies a single nodelocked license) from the compound password. It then automatically installs them at user nodes at which the product so licensed is invoked.
compression
In SNA networking: The replacement of a string of up to 64 repeated characters by an encoded control byte to reduce the length of the data stream sent to the LU-to-LU (logical-unit to logical-unit) session partner. The encoded control byte is followed by the character that was repeated (unless that character is the prime compression character). See also compaction, compaction table.
computer-aided design (CAD)
A process in which the computer system is used as the primary medium for engineering, drafting, or other design work.
computer-aided engineering (CAE)
A process in which the computer system is used as the primary medium for engineering analysis and design.
concatenation
In ptx/SVM: The default plex layout, in which subdisks are joined into a plex to form a linear address space. The first subdisk is filled with written data before the second, the second is filled before the third, and so on.
Conceptual Communications Area (CCA)
Under Construction.
concurrent-access license
In ptx/LICENSE: A type of license administered by the license server. It can be used by different users at any node that is connected to a license server node. Concurrent access licenses allow as many users to use a software product concurrently as there are licenses.
configuration database
In ptx/SVM, a database specific to each disk group that contains all volume, plex, subdisk, and disk media records. The records are replicated onto some or all disks within the disk group, usually with one copy on each disk. Record associations cannot span disk groups.
configuration listing
A display that appears on the console when the system is booted. It includes information such as the hardware found on the system and the amount of memory available.
configure
  1. In UNIX system administration: To build system-configuration files.
  2. In general computer-industry parlance: To implement a computer system in a particular way, selecting from various choices of processing, storage, and input/output devices.
  3. By extension, to enable selectively various options and features of a program so that it operates by default in a particular way.
confirm primitive
In networking: The confirm primitive is passed from the Data Link Service (DLS) provider to the Data Link Service (DLS) user to convey the results of one or more previously associated service requests. The confirm primitive does not necessarily indicate any activity at the remote peer interface. See also Data Link Service (DLS).
Connectionless Network Protocol (CLNP)/Connectionless Network Service (CLNS)
An OSI network-layer protocol/service that does not require a circuit to be established before data is transmitted. CLNP is the OSI equivalent of Internet Protocol (IP). See also Internet Protocol (IP), Open Systems Interconnection (OSI) model.
connectionless service mode
In networking: A mode of data transfer in which data is passed, without prior coordination, from one user to another in self-contained units called "packets" or "datagrams." The packets of transmitted data contain complete address and control information. This mode is inherently less reliable than connection-oriented service. See also connection-oriented service mode.
Connectionless Transport Protocol (CLTP)
Under Construction.
connection-oriented network service (CONS)
A type of networked data communication in which a dedicated connection between two peer entities is established before data is transferred. A connection-oriented service consists of three phases: establishment, data transfer, and release. The two networks exchange address information only while the connection is being established.
connection-oriented service mode
A circuit-oriented mode of data transfer in which data is passed from one user to another over an established connection in a reliable, sequenced manner. The circuit, whether physical or virtual, is dedicated to the communication between those two users until it is released.
connection-oriented transport service (COTS)
A circuit-oriented mode of data transfer in which data is passed from one user to another over an established connection in a reliable, sequenced manner. The circuit, whether physical or virtual, is dedicated to the communication between those two users until it is released.
CONS
See connection-oriented network service (CONS).
console
A terminal connected directly to the computer and used for communication between the operator and the computer.

contention
A condition arising when two or more devices attempt to control a communications path. Examples include microprocessors trying to use the system bus, a memory location, or a peripheral at the same time, and data stations trying to transmit at the same time over a shared channel.
contiguous file
A file in which logically adjacent data blocks are also physically adjacent on the underlying media.
control and status register (CSR)
A register used to control the operation of a device and record the status of an operation, or both.
control bytes
Bytes associated with a physical record that serve to identify the record and indicate such characteristics as length and blocking factor.
control character
A character that the user transmits by holding down <Ctrl> while pressing another key. For example, <Ctrl> and C together transmit an interrupt command.
control object
In OSI networking: One of a number of abstract data structures (objects) that make up the Conceptual Communications Area (CCA). Its main use is to model the exchange of control information. However, the VT Service in OSI's Virtual Terminal model does not limit the type of information to control information only. See also Open Systems Interconnection (OSI) model
control stream
In network programming for UNIX-based systems: In a multiplexer, the upper stream on which a previous i_link ioctl to the associated file (refer to the streamio(7) man page) caused a lower stream to be connected to the multiplexer driver at the end of the upper stream.
controller
  1. A device that directs the transmission of data over the data links of a network.
  2. A hardware interface that interprets system commands for controlling a device.
convergence sublayer (CS)
In OSI networking: One of the two sublayers of the common part convergence sublayer (CPCS) responsible for padding error checking.
Conversational Monitor System (CMS)
A virtual-machine operating system that provides general interactive time sharing, problem solving, and program development capabilities.
conversion
  1. The process of changing from one method of data processing to another.
  2. The process of changing from one form of representation to another; for example, to change from ASCII representation to EBCDIC representation.
copyback cache
A caching scheme in which a processor modifies a piece of data in its cache, but does not immediately write the new value to system memory or to other processor caches. The modified data is written to main memory (and to other processor caches, if needed) when the processor needs the occupied cache space or another processor needs the modified data.
core dump
An image of system main memory that is saved when a system panic occurs or when a program crashes as a result of some error which causes an illegal memory access. A core dump can be ready by a debugger to see where the error occurred.
Corporation for Open Systems (COS)
In OSI networking:
  1. An organization that promotes the use of OSI protocols through conformance testing, certification, and related activities. See also Open Systems Interconnection (OSI) model.
  2. A class of service indicating how an upper-layer protocol wants a lower-layer protocol to treat its messages. See also Open Systems Interconnection (OSI) model.
COS
See Corporation for Open Systems (COS).
COS definition
In SNA networking: A virtual route number in a transmission priority field, used by subarea nodes to determine the optimal route for establishing a given session.
COTS
See connection-oriented transport service (COTS).
covert channel
A communications channel that allows two cooperating processes to transfer information in a manner that violates the system's security policy.
CPCS
See Common Parts Convergence Sublayer. (Under construction)
cpi
See characters per inch (cpi).
CPU
See central processing unit (CPU).
CRC
See cyclic redundancy check (CRC).
CRLF
See carriage return-line feed (CRLF).
cron command
In UNIX-based operating systems: Invokes a utility that schedules the execution of operating-system commands at specific times and intervals.
crontab file
A file that specifies when specific commands should be run by the cron process.
crosspoint switch
The highest performance Fibre Channel fabric. It allows all N_Ports connected to the fabric to communicate with each other. N_Ports connect to F_Ports of the fabric over links. Multiple paths may be open simultaneously between multiple pairs of ports, with all paths communicating at full bandwidth. See also fabric, FC port, F_port, and N_port.
CRT
See cathode-ray tube (CRT).
.cshrc file or cshrc file
A start-up file used by the C shell, executed whenever a new copy of the shell program starts up. It contains aliases and other commands that affect the user's environment.
CS
See convergence sublayer.
CSM
See Central Services Module (CSM).
CSMA/CD (Carrier Sense Multiple Access with Collision Detection)
A medium access method in which a station listens to the medium to determine if another station is currently transmitting a message. The CSMA/CD method also detects the resulting collision when two station transmit simultaneously. Ethernet, for example, is a well-known network based on CSMA/CD technology.
CSR
See control and status register (CSR).
CTERM
See Command Terminal (CTERM).
current directory
The directory in which the user is presently working. In a relative pathname, a dot (.) represents the current directory. See also pathname.
current line
The line on which the cursor is located (in a file that the user is editing).
current usage table
A table containing fileset information, such as the number of blocks currently used by the fileset.
cursor
An indicator, usually a rectangle or underscore, that marks the place at which characters will appear when typed.
Customer Information Control System (CICS)
An IBM communications system that was converted for database handling.
cut buffer
In a windowing environment: A region in computer memory where the display server stores data for clients. The data is typically text that a user has selected in a client window. For example, text cut in an xterm window is stored in the cut buffer.
cyclic redundancy check (CRC)
An error-detection scheme in which extra digits are appended to each data block, producing values which can be compared before and after an operation such as data transmission or readback, to show whether an error has occurred during the operation.
cylinder
A set of tracks on a disk. The read/write head can access all tracks within a cylinder without moving.
cylinder group
Several contiguous cylinders on a disk. The filesystem spreads files and directories throughout its cylinder groups and attempts to store data for a file within a single cylinder group.


D

DAC
See Discretionary Access Control (DAC).
daemon
In UNIX-based operating systems: A routine that runs as a background process and performs a system function. Daemons are typically scheduled by the cron program. See also cron command.
daemonize
In UNIX-based operating systems: To separate a process from the control terminal from which it was invoked.
DAP
See DECnet Data Access Protocol (DAP).
DARPA
See Defense Advanced Research Projects Agency (DARPA).
DAS
See dual-attachment station (DAS).
data block
A collection of data units such as words, characters, or records that are stored in adjacent physical positions in memory or in a peripheral storage device. All the data in a block can be transferred between memory and the storage device with a single instruction.
Data Circuit-terminating Equipment (DCE)
One of two types of hardware connected by an RS-232-C standard connection; the other is a Data Terminal Equipment (DTE) device. A DCE device accepts input from a DTE and transforms the signal in some way before sending it to the receiving device. For example, an external modem--a DCE--accepts input from a microcomputer--the DTE--modulates it, and then sends the data along a telephone connection. See also data terminal equipment (DTE).
Data Communications Processor (DCP)
A circuit board that provides ports for connections to networks and other computer systems.
data-control block (DCB)
Under Construction.
Data Flow Control (DFC) layer
In SNA networking: The functional layer that protects the integrity of the flow of data during a session between two network addressable units (NAUs). See also network addressable unit (NAU), Systems Network Architecture (SNA) functional layers.
Data Link Control (DLC) layer
In SNA networking: The functional layer that consists of the link stations that schedule data transfers over a link between two nodes and perform error control for the link; for example, Synchronous Data Link Control (SDLC). See also Systems Network Architecture (SNA) functional layers.
Data Link layer
In OSI networking: The functional layer that manages transmission, framing, and error control over a single communication link; often referred to as layer 2. See also Open Systems Interconnection (OSI) model.
Data Link Provider Interface (DLPI)
In ptx/LAN: The interface between a Logical Link Control (LLC) driver and other software modules. The ptx/LAN version conforms to the standard developed by AT&T and UNIX International. See also Logical Link Control (LLC).
Data Link Service (DLS)
Under Construction.
Data Link Service access point (DLSAP)
A point at which a Data Link Service (DLS) user attaches itself to a Data Link Service (DLS) provider to access data link services. See also Data Link Service (DLS) provider, Data Link Service (DLS), Data Link Service (DLS) user.
Data Link Service access point (DLSAP) address
An identifier used to differentiate and locate specific DLS user access points (DLSAPs) to a Data Link Service (DLS) provider. See Data Link Service access point (DLSAP), Data Link Service (DLS) provider.
Data Link Service (DLS) data unit
A grouping of Data Link Service (DLS) user data whose boundaries are preserved from one end of a data link connection to the other. See also Data Link Service (DLS).
Data Link Service (DLS) provider
The Data Link layer protocol that provides the services of the Data Link Provider Interface. See also Data Link Provider Interface (DLPI), Open Systems Interconnection (OSI) model.
Data Link Service (DLS) user
The user-level application, or the user-level or kernel-level protocol, that accesses the services of the Data Link layer. See also Data Link Service (DLS), Open Systems Interconnection (OSI) model.
data-network identification code (DNIC)
Under Construction.
data set ready (DSR)
An RS-232-C standard signal used to notify a terminal that the modem (data set) is ready to send and receive data. See also data terminal ready (DTR).
data-synchronous write
A form of synchronous I/O that writes the file data to disk before the write returns, but only marks up the inode for later update. If the file size changes, the inode will be written before the write returns. With this mode, the file data is guaranteed to be on the disk before the write returns, but the inode modification times may be lost if the system crashes.
data-terminal equipment (DTE)
In networking: Hardware--such as computers, protocol translators, and multiplexers--that provides entry and exit points for user data in a communications connection.
data terminal ready (DTR)
An RS-232-C signal used by a terminal to advise a modem that the terminal is ready for operation. See also data set ready (DSR).
database
A collection of structures, each containing units of logically related data, designed to facilitate the storage and control of those units and the definition and manipulation of references among those units.
datagram
In networking: The basic unit of information passed across connectionless service such as a TCP/IP network. Along with the user data, a datagram contains the source and destination addresses, enabling it to be transmitted independently. See also connectionless service mode.
Datapump
A proprietary chip of Vitesse Semiconductor Corporation on the IQ-LINK board that interfaces between the SCI bus and the Pentium bus.
daughterboard
A printed circuit board that is mounted on and electronically connected to a host board, or motherboard. A common usage is in memory-board configurations.
DB-9
The generic term for a standard 9-pin connector.
DB-25
The generic term for a standard 25-pin connector.
DCB
See data-control block (DCB).
DCC
See Dual-Channel Disk Controller (DCC).
DCE
See Data-circuit - terminating equipment (DCE).
DCP
See Data Communications Processor (DCP).
DCP-8804
A MULTIBUS DCP board that provides Symmetry systems with four high-speed serial communications ports for connections to networks and other computer systems. Used with synchronous communications protocols. See also Data Communications Processor (DCP).
DDN
See Defense Data Network (DDN).
DDPN
See Distributed Data-Processing Network (DDPN).
DDS-2 and DDS-3 libraries
Mass-storage tape devices for use with ptx/ESBM.
deadlock
An error condition in which a process cannot continue, because each of two elements of the process is waiting for an action by or a response from the other.
deallocate
To release a resource that is assigned to a specific task.
debug
To detect and eliminate errors ("bugs") in software or hardware.
decision support system (DSS)
A set of related programs and required data to help members of an organization make informed decision by retrieving and analyzing information themselves, without the mediation of database management specialists.
DECnet
Digital Equipment Corporation's network product.
DECnet Data Access Protocol (DAP)
A set of networking protocols for Digital Equipment Corporation's VAX family of computers. Addresses are in the form of (Area Number Node Number).
deconfiguring
In computer installation: Flagging a system board as not to be used by the system. Causes the board not to be checked during autoconfiguration.
decrement
To reduce (a variable) in value, typically by a small amount (usually one).
dedicated line
A connection not requiring dialing to establish communication. The line is permanently connected and always available. Also called leased line, nonswitched line, and private line.
dedicated port
In LAT network architecture: A terminal device used to access local LAT services. See also Local Area Transport (LAT).
default
  1. A value, attribute, or option assigned by the operating system when none has been specified.
  2. The standard way a command performs if not modified by the user.
  3. In ptx/ADMIN: The preset value for a field in the ptx/ADMIN menu system.
  4. In the X Window System: X Window resources; also called "X defaults."
default access control list (ACL)
A template used to generate access control lists (ACLs) for the files within a directory. A default ACL is not used to verify permissions. See also access control list (ACL).
default printer
See system default destination printer.
defect list
A list of problem areas on a disk that have been made inaccessible.
Defense Advanced Research Projects Agency (DARPA)
Formerly the Advanced Research Projects Agency (ARPA). A government agency that provides funding for a variety of projects, such as developing the TCP/IP protocol suite.
Defense Data Network (DDN)
The MILNET and associated parts of the Internet that connect military installations.
defragmentation
A method of consolidating unusably small areas of memory, thus creating areas large enough to satisfy memory allocation requests.
delimiter
  1. A character that separates words or arguments on a command line or in a script. Spaces and tabs are examples of delimiters.
  2. One or more characters that separate comments from program code. In the C programming language, comments are delimited by /* and */.
delta
A change between two instances of an item, typically used to describe a software upgrade. See also delta installation.
delta installation
A software installation procedure that compares the files on the distribution medium with the files currently on the system, replacing only those current system files that are not identical to the new files.
destination printer
A particular printer or class that receives print requests.
See also system default destination printer.
destination printer, default
See system default destination printer.
destructive service
Any kind of data transport service in which loss of data can occur without notification. Some types of connectionless service are destructive. See also connectionless service mode.
/dev directory or dev directory
See device node.
device
A disk drive, tape drive, cartridge drive, printer, modem, or other computer-related hardware. See also backup device.
device address
The means by which a host identifies a device.
device allocation
In DYNIX/ptx, a security feature that can be used to control user access to tape or CD devices.
device-dependent
Describing software or hardware that uses (or pertains to) some characteristic of a particular device or device type.
device driver
A special-purpose program used to control a specific peripheral device or a set of devices (disk drives, tape drives, printers, and so on). Device drivers are typically part of the operating system.
device naming database
In DYNIX/ptx, a database that contains information such as the device name and number, the configuration type, and the uuid for each device on the system.
device node
In UNIX-based operating systems: A file in the /dev directory. Each node represents a single device and acts as the interface between the operating system (kernel) and the corresponding device. Device nodes are created automatically when the system is booted, and they can also be created by the system administrator. Also called "device special file."
device special file
See device node.
device-specific
See device-dependent.
DFC layer
See Data Flow Control (DFC) layer.
DHCP
See Dynamic Host Configuration Protocol.
diagnostics
Stand-alone programs that test the hardware components of a system.
dial code
An abbreviation that represents a portion of a telephone number; used by UUCP.
dial line
See switched line.
dialog
A two-way conversation between programs, protocols, or systems.
dial up
To use a dial or pushbutton telephone to initiate a station-to-station telephone call.
dial-up
Describing a port or modem that accepts calls.
diary RAM
A data-capturing feature of the system firmware that allows on-demand recording of text messages (writing) or querying of the textual contents (reading). Also the name of the electronic component that contains the changeable data.
DIMM
See Dual In-line Memory Module (DIMM).
direct extent
In the Enhanced File System (ptx/EFS): An extent that is referenced directly by an inode.
direct I/O
An unbuffered form of input/output that bypasses the kernel buffering of data. With direct I/O, the filesystem transfers data directly between the disk and the user-supplied buffer.
direct link
Hardware that allows computers located near each other to communicate. For example, a cable run between the serial ports of two computers, allowing them to engage in UUCP conversations.
direct memory access (DMA)
A feature used to enhance the performance of some computer system components. DMA allows a device to manipulate information in the system's memory directly, without involving a central processing unit (CPU). Many peripherals and components make use of DMA.
directory
A type of file that groups and organizes other files. You can create a directory, add files to it, remove files from it, and remove the directory itself.
dirty-region logging (DRL)
In ptx/SVM: A fast recovery mechanism for mirrored volumes. DRL logically divides a volume into a set of regions and keeps track of the regions that are being written to (dirty regions). Each write to a region of a volume is also written to a logging subdisk. If the system crashes before it writes the data to all of the plexes of the volume, when the system restarts, ptx/SVM will recover only those regions of the volume still flagged on the logging subdisk. This saves resynchronization time, because only a small fraction of data has to be copied, not the entire volume. See also plex, subdisk, volume.
disable
To make a system device (such as a printer or disk drive) or feature unavailable for use by the operating system and other programs.
disconnect function
A function used by either the source or target task for orderly termination of the logical link.
Discretionary Access Control (DAC)
A method of controlling user access to data. In DAC systems the owner of a file or directory can determine the type of access to be allowed to other users. The operating system provides two methods for discretionary access control: normal file permissions and access control lists (ACLs). See also access control list (ACL), file access rights.
disk
A magnetic storage medium.
disk access name
In ptx/SVM, the name used to access a hysical disk.
disk access record
In ptx/SVM, a configuration record used to specify the access path to a particular disk.
disk geometry
The physical characteristics (such as the number of sectors per track, tracks per cylinder, and so on) that apply to a specific model of disk.
disk group
In ptx/SVM, a group of disks, which may or may not share a common configuration. Disk groups contain configuration database information for the disks within the disk group only, allowing smaller configuration databases throughout ptx/SVM. Record associations cannot span disk groups; therefore, subdisks defined on a disk in one disk group cannot be associated with a volume in another disk group.
disk media name
A logical or administrative name chosen by the administrator for a disk. The disk media name can also match the disk access name.
disk media record
In ptx/SVM, a configuration record that identifies a particular disk by disk ID and gives that disk a logical name.
disk mirror
A logical disk partition that maintains identical copies of data on two physical disk partitions. As with conventional disks, a mirror may contain filesystems or raw data. Mirror operation is transparent to users and applications.
disk multiplexer board (OK board)
A component of the Symmetry SMD-E disk drive subsystem that routes signals and data from the DCC board to the attached disk drives. The disk multiplexer board resides in its own sliding tray in a Symmetry expansion cabinet.
disk quota
A limit on the amount of disk space and the number of files a user can own.
disk sector
A unit for measuring the storage capacity of a disk. A disk sector contains 512 bytes, which is the smallest indivisible transfer size for disks.
disk type
A name that identifies a specific kind of disk. Disk type corresponds to the model name assigned by the disk manufacturer.
diskette
A removable magnetic storage medium, usually with a smaller capacity than a disk.
display console
A console that must include at least one display device and may also include one or more input units, such as an alphanumeric keyboard or light pen.
display server
In ptx/XWM: A program that controls a keyboard, a pointer, such as a mouse, and one or more screens. A display server handles I/O between a display system and client applications.
display system
In ptx/XWM: The combination of graphics display, hardware, and X display-server software that provides display services for client applications.
dissociation
In ptx/SVM : Removal of the link between a subdisk and its associated plex or between a plex and its associated volume.
Distributed Data-Processing Network (DDPN)
A network in which some or all of the processing, storage, control, and input/output functions are dispersed among its nodes.
distributed-memory multiprocessor
A type of computer system in which each processor has its own independent memory system. Each processor in such a system is almost entirely self-sufficient because of its local memory, and typically communicates with the other processors only to read initial code and data and to write final results. This type of design is called ''loosely coupled.''
distributed shared memory (DSM)
"Shared memory" is a logical architecture for parallel computing in which multiple processors run a single copy of the operating system. The operating system presents the illusion of a single large physical memory ("single address space") and a single very fast processor to all applications running on top of the operating system. Distributed shared memory preserves this illusion, even though the memory may be physically distributed among many processors.
distributed symmetrical multiprocessing (DSMP)
Under Construction.
Distributed Terminal Interface (DTI)
An interface for connecting many user terminals to a system.
DLC Layer
See Data Link Control (DLC) Layer.
DLPI
See Data Link Provider Interface (DLPI).
DLS provider
See Data Link Service (DLS) provider.
DLS user
See Data Link Service (DLS) user.
DLSAP
See Data Link Service access point (DLSAP).
DLSAP address
See Data Link Service access point (DLSAP) address.
DLT4000 tape library
A digital linear tape (DLT) library that provides backup storage for IBM NUMA and S5000 systems.
DMA
See direct memory access (DMA).
DNIC
See data-network identification code (DNIC).
DNS
  1. See domain name server (DNS).
  2. See Domain Name System (DNS).
domain
  1. In SNA networking: All the nodes and devices managed by the system services control point (SSCP) in a host node. See also Systems Network Architecture (SNA), system services control point (SSCP).
  2. In the domain name system, part of the naming hierarchy. Domain names consist of symbolic names (labels) separated by periods (dots).
domain name server (DNS)
Under Construction.
Domain Name System (DNS)
In networking: The distributed database system used to map symbolic machine names to IP addresses. See also Internet Protocol (IP).
domain-specific part (DSP )
The part of the Connectionless Network Service (CLNS) address that contains an area identifier, a station identifier, and a selector byte. See also Connectionless Network Service (CLNS).
domin_all
A site security parameter used to label files and directories to which no user may have access. domin_all has a media access control (MAC) label or MAC label alias associated with it.
download
To transfer data from a large (typically remote) computer to a small (typically local) computer.
downstream
The direction from a stream head toward a driver. See also driver.
drive
Generally a disk drive. Sometimes used in reference to a tape drive, CD-ROM drive, or other mass-storage device.
driver
  1. The queue pairs at the end of the stream closest to an external interface. The principal functions of the driver are handling any associated device and transforming data and information between the external interface and the stream.
  2. A driver can be a device driver, which handles physical devices, or a pseudodevice driver, not directly associated with a device, which performs functions internal to a stream. Multiplexers and error and trace loggers are pseudodevice drivers.
DSM
See Distributed Shared Memory (DSM).
DSMP
See distributed symmetrical multiprocessing (DSMP).
DSP
See domain-specific part (DSP).
DSR
See Data Set Ready (DSR).
DSS
See decision support system (DSS).
DTE
See data-terminal equipment (DTE).
DTI
See Distributed Terminal Interface (DTI).
DTP
See desktop publishing (DTP).
DTR
See data terminal ready (DTR).
dual-attachment station (DAS)
In networking: A station that offers two attachments to a network, to both an upstream and a downstream neighbor, and is therefore capable of accommodating a dual ring.
Dual-Channel Disk Controller (DCC)
A set of circuit boards designed to control and communicate with SMD-E disk drives. The DCC is used in Symmetry 2000/400 and 2000/700 systems, and in S27 and S81 systems.
Dual In-line Memory Module (DIMM)
A small circuit board that carries memory chips, with connector pins on both sides of the board. Each pin can be connected to a different memory chip, making it possible to access several memory chips at one time, and so create a wider data path. The DIMM is the technology used for expanding memory in IBM NUMA computer systems. See also Single In-line Memory Module (SIMM).
dump
In UNIX-based operating systems: To save all the data in processor memory or in a data-storage device to some other storage medium or device, usually when an error has been detected in a program or operating system.
dump string
In UNIX-based operating systems: The fully specified pathname of a program that copies an image of system memory to a disk when the system is being rebooted after a panic. See also pathname.
duplex
In data communication, pertaining to a simultaneous two-way independent transmission in both directions. Synonym for full-duplex.

See also half-duplex.

duplex cable
In data communications: Outbound and inbound signal-carrying fibers packaged together in a common cable assembly.
duplex coupling
In IBM NUMA hardware: A mechanical device for connecting two fiber-optic duplex cables in series. The coupling accomodates SC connectors only on the ends of the fibers.
dynamic allocation
An allocation technique in which the resources assigned for the execution of computer programs are determined by criteria applied at the moment of need.
Dynamic Host Configuration Protocol (DHCP)
In TCP/IP networking: A protocol, based on BOOTP, that allows client systems to determine values for all the configuration parameters needed to communicate on a TCP/IP network. It supports more configuration parameters than BOOTP and allows for temporary allocation of IP addresses.
dynamic nodelocking
In ptx/LICENSE: The automated licensing of multiple nodes through the use of compound passwords.