cache
A place where data is stored so that it does not need to be read from a slower device. Copies of frequently used disk sectors are stored in RAM so they can be accessed without accessing the hard disk.
case sensitivity
The ability of the operating system to distinguish between uppercase and lowercase letters. MS-DOS commands are not case-sensitive; UNIX commands are.
cathode-ray tube
See CRT
CD-ROM (compact disc read-only memory)
A disc similar to an audio compact disc, but it contains computer data.
central processing unit
See CPU
CGA (Color Graphics Adapter)
An early color graphics adapter standard with resolutions of 320 pixels by 200 pixels or 640 x 200. CGA supported no more than four colors.
chip
The ultimate integrated circuit; contains the complete arithmetic and logic unit of a computer. See microprocessor
chip set
A group of computer chips or ICs (integrated circuits) that, when working in harmony, manage and control the computer system. This set includes the CPU and other chips that control the flow of data throughout the system. Typical chip sets consist of a bus controller, a memory controller, data and address buffer, and a peripheral controller.
CISC (complex instruction set computing)
A computer with many different machine-language instructions.
client
A computer that connects to a network and uses the available resources provided by the server.
clock
Establishes the maximum speed at which the processor can execute commands. Not to be confused with the clock that keeps time.
clock speed
Measured in megahertz (MHz)-millions of cycles per second-it is the speed at which a clock can cycle, or how fast a CPU can execute a command.
clone
A term that derives from the early days of personal computing used to denote a computer compatible with, but not manufactured by, IBM.
clusters
A unit of storage on a mass-storage device such as a hard disk drive or CD-ROM disc. On a hard drive a cluster usually consists of two to eight sectors. The actual amount of data a cluster can hold is dependent on the operating system and controller type.
CMOS (complementary metal-oxide semiconductor)
A chip that gets its name from the way it is manufactured and not the information it holds. Unlike other ROM chips, CMOS chips store data that is read by the BIOS to complete the programs needed to talk to changeable hardware.
CMOS battery
Prevents unique information about the setup of the computer from being lost when the power is turned off. Also maintains the external clock time (not to be confused with the CPU's clock).
coaxial cable
Made of two conductors that share the same axis. The center is a relatively stiff copper wire encased in insulating plastic. A wire-mesh tube around the insulation serves as shielding. The outside is a tough insulating plastic tube.
code
A way of representing information on a machine or in some physical form so that the information can be placed on the external data bus to be read by all devices. Also, statements (source code) written in a programming language, which are compiled into executable instructions (object code).
cold boot
The process of restarting a computer after it has been powered down.
COM1, COM2
The names assigned to the first two serial ports on a PC.
command mode
The character mode used in an operating system such as Microsoft Windows, MS-DOS, or UNIX that has a prompt and in which actions take place while the user enters text strings to execute commands.
compression
"Squeezing" a file down in size by getting rid of all the bits it doesn't really need. Many files (especially those with graphics) are very large and require a long time to travel over the Internet, so they are best compressed before sent.
conferences
Different areas of conversation in an e-mail system that are topic-specific rather than individualized.
conventional memory
The memory area between 0 and 640 KB that is designated for running MS-DOS and MS-DOS applications.
cookie
A special message stored on a computer that allows a Web site to keep track of when a user has visited that site.
coprocessor
A separate circuit inside a computer that adds additional functions to the CPU or handles extra work while the CPU is busy.
CPU (central processing unit)
The part of a computer in which arithmetic and logical operations are performed and instructions are decoded and executed. It controls the operation of the computer.
CRT (cathode-ray tube)
The main component of a monitor. One end of the tube is a very slender cylinder containing an electron gun(s). The fatter end is the display screen.
cursor
When entering data, whether in an application or in an MS-DOS command, the cursor (often a small flashing line) indicates the place at which the characters will be inserted.