- .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
-
- Cancel all operations associated with a transaction. Back out all
changes to database contents.
- 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
-
- The means by which a host identifies a device.
- A network path used to route E-mail and news between machines.
- 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
-
- See application process (AP).
- 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)
-
- 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.
- 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
-
- A set of rules for the design of a network.
- A synonym for topology.
- An overview of the relationship among the hardware or software
components of a computer system.
- archive
- See back up, backup.
- argument
-
- A value passed between programs or functions that specifies how,
or upon what, they are to operate.
- 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
-
- 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.
- 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
-
- An accumulation of data to be processed.
- A group of records or data-processing jobs brought together for
processing or transmission.
- 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
-
- In SNA networking: A request to activate a session between two
logical units (LUs). See also BIND type,
logical unit (LU).
- 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)
-
- A single-digit binary number.
- 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
-
- A rectangular area on the display composed of pixels, each of
which is white, black, or, in color displays, a color.
- 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
-
- In packet-switching networks: A system connecting two or more
systems or networks and forwarding packets among them, using their physical
addresses.
- 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.
- 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
-
- (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.
- (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
-
- An electronic circuit used to transfer information among computer
components and devices.
- 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
-
- 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.
- 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
-
- See audit class.
- See client class.
- 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
-
- The requesting program in a system in which a program at one site
sends a request to a program (the server) at another site.
- 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.
- 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."
- 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
-
- The smallest unit of time recognized by the central processing
unit (CPU)--typically a few hundred-millionths of a second.
- 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
-
- The routine that is called when a module is popped from a stream.
- The driver routine that is called when a driver is closed.
- CLTP
- See Connectionless Transport Protocol (CLTP).
- cluster
-
- 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.
- 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
-
- In UNIX system administration: To build system-configuration
files.
- 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.
- 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
-
- A device that directs the transmission of data over the data
links of a network.
- 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
-
- The process of changing from one method of data processing to
another.
- 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:
- An organization that promotes the use of OSI protocols through
conformance testing, certification, and related activities. See also
Open Systems Interconnection (OSI) model.
- 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
-
- A value, attribute, or option assigned by the operating system
when none has been specified.
- The standard way a command performs if not modified by the
user.
- In ptx/ADMIN: The preset value for a field in the ptx/ADMIN menu
system.
- 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
-
- A character that separates words or arguments on a command line
or in a script. Spaces and tabs are examples of delimiters.
- 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
-
- See domain name server (DNS).
- See Domain Name System (DNS).
- domain
-
- 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).
- 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
-
- 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.
- 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.