Computer Terms - Letters C through D

Cache: keeps data the processor is likely to need quickly close at hand; increases processor operation speed

CAD/CAM (computer-aided design/computer-aided manufacturing): software used to design products such as electronic circuit boards in computers

Campus backbone: connects building LANs together

CD-R (compact disc - recordable): special type of CD-ROM that can be written onto by any computer with a recording drive; can only be written onto once

CD-ROM (compact disc read-only memory): optical storage device read by lasers; can hold up to 700 megabytes of data

CD-RW (compact disc - rewritable): special type of CD-ROM that can be written onto by any computer with a recording drive; can be written onto more than once

CIR (committed information rate): describes the user information transfer rate the network supports during normal network operations

CLEC (competitive local exchange carrier): In the US, a telecommunications provider company (also called a carrier) that competes with other, already established carriers (the local telephone company)

Client/server architecture: network where some computers are dedicated clients (workstations) and some are dedicated servers; information is centralized on the server, and an administrator sets policies and manages it

CMOS (complementary metal-oxide semiconductor) RAM: requires very little power; maintains information even when the computer is off

Collision: occurs when several network users communicate at the same time and interfere (collide) with one another

Collision domain: logical network segment where data packets can "collide" with one another for being sent on a shared medium, in particular in the Ethernet networking protocol

Computer networking: a combination of hardware and software that lets the various computers in an organization communicate with one another

Computer operating system (OS): special computer program that provides an environment in which other programs can use the computer’s central processor and the attached input/output devices

Connectivity devices: bring users of the network into contact with one another

Constant bit rate (CBR): transmission that uses a set amount of network capacity on a continual basis; used when the arrival of the information is time-sensitive

Convergence: the merging and sometimes clashing of voice and data

CPE (customer premises equipment): generally refers to telephones, DSL or cable modems, or purchased set-top boxes for use with communication service providers’ services

CPS (cycles per second): measure of how frequently an alternating current changes direction; has been replaced by the term hertz (Hz)

CPU (Central Processing Unit): the brain of the computer system where calculations and decisions are made; also referred to as the processor

CPU Speed: how fast the CPU works

CSU (channel service unit): provides a loopback function for telephone company testing, and checks bipolar signal generation

CRC (cyclic redundancy check): method of checking for errors in data that has been transmitted on a communications link; a function used to produce a Checksum against a block of data

CS (convergence sublayer): particular protocols that are responsible for gathering and formatting higher layer information so it can be processed by the lower layers

CSMA/CD (carrier sense multiple access/collision detect): set of rules for determining how network devices response when two devices collide

D (data) channel: used for common channel signaling by both the telephone company switch and the customer equipment; provides the call signals that set up B channel connections

DACS (digital access and cross-connect system): a piece of telecommunications equipment used for routing T1 lines; can cross-connect any T1 line in the system with any other T1 line in the system

Data: information manipulated inside the computer in the form of bits and bytes

Datagram: data packet that is sent over an IP network; associated with the network layer when communication protocol is connectionless

DCE (data communications equipment OR data circuit-terminating equipment): a device that communicates with a data terminal equipment (DTE) device in a particular standard

DDP (datagram delivery protocol): a member of the AppleTalk networking protocol suite, mainly responsible for socket-to-socket delivery of datagrams over an AppleTalk network

DE (discard eligibility): signal used to identify less important data traffic that can be dropped during periods of congestion on the system

DLCI (data link connection identifier): a channel number that tells the network how to route the data

DMA (direct memory access): a feature that allows certain hardware subsystems in a computer to access system memory for reading and/or writing independently of the CPU; can include disk drive controllers, graphics cards, network cards, and sound cards

DOS (disk operating system): a family of closely related operating systems (COS) that ran on IBM PC type hardware.

DNA (digital network architecture): a set of specifications or protocols created by Digital Equipment Corporation (DECnet) that evolved into one of the first peer-to-peer network architectures

DNS (domain name system): service that connects a domain name to an IP address

DRAM (dynamic random access memory): primary choice for holding large amounts of information due to its inexpensive cost; must be refreshed or rewritten frequently (about every 386 milliseconds)

DS0 (digital signal, level 0): basic digital signaling rate of 64 kbit/s, corresponding to the capacity of one voice-frequency-equivalent channel

DS1 (digital signal, level 1): also known as T1; widely used to transmit voice and data between devices

DSL (digital subscriber line): technology that delivers digital data transmission over the wires of a local telephone network

DVD (digital versatile disc): can hold over seven times as much information as CDs

DWDM (dense wavelength-division multiplexing): an optical technology used to increase bandwidth over existing fiber optic backbones (see building backbone, campus backbone)