DPI (Dots Per Inch)

Units used to measure the resolution of images on many printers and scanners. Keep in mind that dpi is an exact measurement in laser printers but often used as an approximation in ink-jet printers.

Dynamic Random Access Memory (DRAM)

Memory that requires a refresh signal to be sent to it periodically.


The ability to transfer a file from a remote computer to your computer.

DOS Protected Mode Interface (DPMI)

Specification that allows multiple applications to access extended memory at the same time. Most memory manager producers and application developers have endorsed this standard. Microsoft Windows uses the DPMI specification.

DOS Prompt

Displays the active drive letter (for instance, C:) and directory. This indicates that the operating system is ready to accept the next command.

Disk Operating System (DOS)

A text-based operating system used by most early PCs to manage hardware, data, and applications.

Data Link Control (DLC)

A protocol developed by IBM to connect token-ring-based workstations to IBM mainframe computers. Printer manufacturers have adopted the protocol to connect remote printers to network print servers.


A location where files are grouped together on the disk. In the Microsoft Windows environment and Apple Macintosh operating systems, these are known as folders.

Direct Memory Access (DMA)

Allows a peripheral device to access the memory of a computer directly, without going through the CPU (central processing unit). This speeds up the transfer of data to or from external devices.

Device Driver

A program that extends the operating system to support specific devices.

Define Defragmentation - What is Defragmentation

Running a program to organize the files on a hard disk so that the various clusters of data for each file are once again contiguous. This helps to speed up the hard disk.

Default Drive

The active drive on the computer. Each drive has its own letter designation. Unless otherwise specified, any commands are performed on the default drive.

DDE (Dynamic Data Exchange)

A Microsoft Windows data exchange protocol that allows for the automatic updating of a file or open application when the source is modified.

Data Communications Equipment (DCE)

The receiver in a telecommunications connection.

Define Data Bus - What is Data Bus

A group of parallel conductors (circuit traces) found on the motherboard that is used by the CPU (central processing unit) to send and receive data from all the devices in the computer. Also called the external data bus.

Define Cursor - What is Cursor

When entering data, whether in an application or at an MS-DOS command prompt, the cursor (often a small flashing line) indicates the place at which the characters will be inserted.

Define CRT - What is 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 wider end is the display screen.

Define CPU - What is Central Processing Unit

The part of a computer that controls the arithmetic and logical operations and decoding and executing instructions.

Define Coprocessor - What is Coprocessor

A separate circuit inside a computer that adds additional functions to the CPU (central processing unit) or handles extra work while the CPU is busy.

Define Conventional Memory - What is Conventional Memory

The memory area between 0 and 640 KB that is designated for running MS-DOS and MS-DOS applications.

Define Conferences - What is Conferences

Different areas of conversation in an e-mail system that are topic-specific rather than individualized.

Define Compression - What is Compression

"Squeezing" a file down in size by getting rid of all the bits that are not really needed. 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.

Define Command Mode - What is Command Mode

The character mode used in an operating system such as Microsoft Windows, MS-DOS, or UNIX that has a prompt where the user enters commands.

Define COM1, COM2 - What is COM1, COM2

The names assigned to the first two serial ports on a PC.

Define Cold Boot - What is Cold Boot

The process of restarting a computer after it has been powered down.

Define Code - What is 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 that are compiled into executable instructions (object code).

Define Coaxial Cable - What is 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.

Define CMOS Battery - What is 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).

Define CMOS (Complementary Metal-Oxide Semiconductor) - What is CMOS

A form of read-only memory chip that gets its name from the way it is manufactured and not the information it holds. CMOS chips are used to store data that is read by the BIOS (basic input/output system) to obtain information on hardware configurations.

Define Clusters | What is Clusters

A unit of storage on a mass-storage device such as a hard disk drive or CD-ROM. 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.

Define Clone | What is Clone

A term that derives from the early days of personal computing used to denote a computer compatible with, but not manufactured by, IBM.

Define Clock Speed | What is 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 (central processing unit) can execute a command. With faster CPUs, the term is now migrating to gigahertz (GHz).

Define Chip Set | What is Chip Set

A group of computer chips or integrated circuits (ICs) that, when working in harmony, manage and control the computer system. This set includes the CPU (central processing unit) 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.

Define Chip | What is Chip

The ultimate integrated circuit; contains the complete arithmetic and logic unit of a computer.

Define CGA (Color Graphics Adapter) | What is CGA (Color Graphics Adapter)

An early color graphics adapter standard with resolutions of 320 pixels by 200 pixels or 640 × 200. CGA supported no more than four colors.

Define CD-ROM | What is CD-ROM

CD-ROM (Compact Disc Read-Only Memory) - A disc similar to an audio compact disc containing computer data.

Define Case Sensitivity | What is 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.

Define Cache | What is 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 (random access memory) so they can be accessed without accessing the hard disk.

Define Byte | What is Byte

A group of 8 bits that represents 1 character of information (for instance, pressing one key on the keyboard). A byte is the standard unit for measuring memory in a microprocessor. Memory size is measured in terms of kilobytes (KB) or megabytes (MB). 1 KB of RAM is 1024 bytes; 1 MB is approximately one million bytes.

Define Bus Network | What is Bus Network

A network in which all computers are connected to a single linear cable. Both ends of the cable must be terminated. Because there is no central point, it is harder to isolate problems in a bus network than in a star network topology.

Define Bus Mastering | What is Bus Mastering

The ability of a device to control its own data bus, only making use of the main system bus when data must be sent to the CPU or another device. This reduces CPU and system bus traffic, improving overall performance.

Define Bus | What is Bus

The main communication avenue in a computer. It consists of a set of parallel wires that are connected to the CPU (central processing unit), memory, and all input/output devices. The bus can transmit data in either direction between any two components. If a computer did not have a bus, it would need separate wires to connect all the components.

Define Browser | What is Browser

Software used to navigate the World Wide Web, such as Microsoft Internet Explorer, Google Chrome, Mozilla Firefox and Opera.

Define Broadband | What is Broadband

A network with high bandwidth (sometimes defined as greater than 256 bps).

Define Bridge | What is Bridge

A device that provides communication between two or more network segments, thereby forming one logical network.

Define BPS (Bits Per Second) | What is BPS (Bits Per Second)

The speed at which a modem transmits data. Typical rates are 14,400, 28,800, 33,600, and 56,600 bps. This represents the actual number of data bits that can be transmitted per second.

Define Boot Up | What is Boot Up

To start a computer; drawn from the phrase "pulling oneself up by one's own bootstraps."

Define Boot Partition | What is Boot Partition

A hard disk partition containing the portion of the operating system needed to launch the operating environment.