DAT
Digital Audio Tape. The most common type of tape backup.

Daughterboard
A board that attaches to (rides piggyback on) another board, such as the motherboard or an expansion card. For example, you can often add a daughtercard containing additional memory to an accelerator card.

Database
A file created by a database manager that contains a collection of information organized into records, each of which contains labeled categories (called fields).

DCS
Desktop color separation. An image format consisting of four separate CMYK PostScript files at full resolution, together with a fifth EPS master for placement in documents.

DDN
Defense Data Network. A global communications network serving the US Department of Defense composed of MILNET, other portions of the Internet, and classified networks which are not part of the Internet. The DDN is used to connect military installations and is managed by the Defense Information Systems Agency (DISA).

DEC
Digital Equipment Corporation.

Decompression
The expansion of compressed image files. See also lossy and non-lossy.

Dedicated line
A telephone or data line that is always available. For example, a leased telephone line can be dedicated for computer data communications. This line is not used by other computers or individuals, is available 24 hours a day, and is never disconnected.

Default Route
A routing table entry which is used to direct packets addressed to networks not explicitly listed in the routing table.

Densitometer
A measuring instrument that registers the density of transparent or reflective materials. Colors are read as tonal information. See also colorimeter and spectrophotometer.

Density
Density is a brightness control to lighten or darken a printout to more closely reflect its screen appearance and to compensate for deficiencies in toner or paper quality.

Descreening
Removal of halftone dot patterns during or after scanning printed matter by defocusing the image. This avoids moire patterning and color shifts during subsequent halftone reprinting.

Dialog box
A window that displays additional options or questions when a command is chosen.

Dial-up line
A communication connection from your computer to a host computer over standard phone lines. Unlike a dedicated line, you must dial the host computer in order to establish a connection. Dial-up line is currently the most popular form of Net connection for the home user.

Dichroic Mirror
A special type of interference filter, which reflects a specific part of the spectrum, whilst transmitting the rest. Used in scanners to split a beam of light into RGB components.

Digital
Data or voltages consisting of discrete steps or levels, as opposed to continuously variable analog data.

Digitizers
A machine which converts analog data into digital data on a computer (such as a scanner digitizing pictures or text).

DIP switches
Dual Interface Poll switches allow for either an ON or OFF setting with any number of circuits. DIP switches commonly allow you to change the configuration of a circuit board to suit your particular computer.

Direct connection
A permanent communication connection between your computer system (either a single CPU or a LAN) and the Internet. This is also called a leased line connection because you are leasing the telephone connection from the phone company. A direct connection is in contrast to a SLIP/PPP or dial-up connection.

Direct-To-Plate
Direct exposure of image data onto printing plates, without the intermediate use of film.

Direct-To-Press
Elimination of intermediate film and printing plates by the direct transfer of image data to printing cylinders in the press.

Directory
A system that your computer uses to organize files on the basis of specific information.

Disk Defragmenter
Arranges the blocks of information for a file into adjacent blocks on your hard drive, which may significantly improve the file access times.

Dmax
The point of maximum density in an image or an original.

Dmin
The point of minimum density in an image or an original.

DNS
Domain Name System. A general purpose distributed, replicated, data query service. Its principal use is the lookup of host IP addresses based on host names. The host names are also known as domain names. Some important domains are: .COM (commercial), .EDU (educational), .NET (network operations), .GOV (U.S. government), and .MIL (U.S. military). Most countries also have a domain. For example, .US (United States), .UK (United Kingdom), .AU (Australia).

Domain Name Server
A computer that converts host names, such as rohan.sdsu.edu to its corresponding IP Address, such as 191.130.1.10. An SDSU computer provides this service any time mail is sent or received and permits users to use TELNET and FTP between SDSU and other sites.

DOS
Disk Operating System. The operating system used on IBM personal computers and compatible machines.

Dotted Decimal Notation
The convention for writing 32-bit IP Addresses as a set of four 8-bit numbers written in base 10 with periods separating them.

Down-Sampling
The reduction in resolution of an image, necessitating a loss in detail.

Download
To retrieve a file from another computer using a modem.

dpi
Dots Per Inch. A measure of the resolution of a printer, scanner, or monitor. It refers to the number of dots in a one-inch line. The more dots per inch, the higher the resolution.

Driver
A piece of software that tells the computer how to operate an external device, such as a printer, hard disk, CD-ROM drive, or scanner. For instance, you can't print unless you have a printer driver. Hard disk drivers are invisible files that are loaded into memory when you start the computer, while scanner drivers are usually plug-ins accessed from within a particular application.

Drum Scanner
Early drum scanners separated scans into CMYK data, recording these directly onto film held on a second rotating drum.

DTP
Desktop Publishing.

Dump
Back-up of data.

Duplex (Full, Half)
Full duplex is data is flowing in both directions at the same time. When Remote echo is ON communication is occurring in full duplex. Half Duplex has data moving in only one direction at a time (Local echo is ON).

DXF
Drawing Interchange Format used for Macintosh graphic files. The standard file-exchange format for 3-D and CAD programs.

Dye Sublimation
A printing process using small heating elements to evaporate pigments from a carrier film, depositing these smoothly onto a substrate.