ACCC Glossary of Computer Terms, D-H

Contents

D | E | F | G | H

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List of Defined Words

DS-1 and DS-3
DARPA
DASD
Dataset
Dates, ISO 8601
Debug
Default
Descenders
Dial-up lines
Disk Drive
DISSPLA
Distributed computing
DNS
Domain style name
DOS
Dots per inch
Download
Driver
Duplex
DSL
DSR
EBCDIC
Echo or Echoplex
Editor
Electronic Form
Electronic Mail
EIA
EPS file
Email account
Email address
Email program
Emoticon
Emulation
Encoding
Encrypt
Ethernet
Eudora
EVL
EXCP
Fast Ethernet
FDDI
Fiber-optic cable
File
File Identifier or Fileid
File server
Finger
Fixed Pitch Fonts
Flame
FLOP
Floppy Disk
FM Synthesis
Folio
Font
Footer
Foreground
FORTRAN
FTP
Full Screen
Full duplex
Gateway
Generic Font
GIF
Gigabit Ethernet
GML
Gopher
GPSS
Graphics
Half duplex
Handshaking
Hard copy
Hardware
Hard disk
Header
HELP
Host
HSM
HTML
Hub
Hypermedia
Hyphenation

+--+ D +--+

DS-1 and DS-3

Digital Switching; the transmission standards used on T1 and T3 lines, respectively; see also T1 and T3.

DARPA

Defense Advanced Research Projects Agency: The US government agency that funded research and experimentation which lead to the Internet network. See ARPANET.

DASD

Direct Access Storage Device. A data storage device such as a magnetic disk storage unit which allows the operating system to directly access specific data stored on it without having to read through the data before it. This is as opposed to a sequential access device such as magnetic tape.

Dataset

See File.

Dates, ISO 8601

See ISO 8601 Dates.

Debug

The process of finding and eliminating software or hardware "bugs" (errors).

Default

The assumed value or action taken when no explicit one is specified.

Descenders

A text formatting term: The portion of any character which extends below the baseline. See also Ascenders and Baseline.

Dial-up lines

A telephone line reserved for communication between the computer and remote terminals. When you call a dial-up line, the computer answers and a connection is made which enables you to logon to your account. Dial-up lines enable you to use a computer system from any location that has a telephone, a modem or coupler, and a terminal or a microcomputer running a terminal emulation program. See ACCC Dialin Services for more information.

Disk Drive

A very fast input/output device that consists of one or more spinning magnetic disks. A moving arm allows direct read or write access to data recorded on the disks.

DISSPLA

The DISSPLA graphics package is a library of FORTRAN subroutines. It was designed to be used by scientific and business programmers. The DISSPLA library routines must be called from a user written and executed program (written in FORTRAN, or another higher level language such as Pascal or PL/I that supports FORTRAN subroutine calls). See the Inform DISSPLA menu.

Distributed computing

See client-server computing.

DNS

Domain Name System or Service. The Internet service that translates Internet domain names to IP addresses. For more information, see internet.com's PC Webopaedia on DNS. See also IP address.

Domain style name

See Internet address.

DOS

Disk Operating System: The name of the operating systems on most brands of personal computer contains the acronym DOS. Often when DOS is used without further description, the operating system being referred to is either PC DOS, the operating system used to be used on most IBM personal computers, or MS DOS, the variety of DOS that runs on IBM compatible computers.

Dots per inch

See Resolution.

Download

To transfer information stored in a remote computer to your (local) microcomputer.

Driver

When information is passed from one type of device to another, usually the electrical and mechanical requirements of the two devices are different; software drivers are used to translate data which is to be sent another device so that device can properly process it. (For example, a printer specific driver may be used to prepare a document formatted by a word processing package for printing on different types of printers, or the same printer used in different modes.)

Duplex

(1) A text formatting term: Printing on both sides of the paper. (2) A computer communications term: Half duplex: data transmission in only one direction at a time; and Full duplex: simultaneous data transmission in both directions.

DSL

A type of broadband data transmission that uses standard copper telephone lines; see Connecting from Home.

DSR

Data Set Ready: When using DCE (Data Communications Equipment; a modem is a common example), the DSR indicates that the DCE is ready to use.

+--+ E +--+

EBCDIC

Extended Binary Coded Decimal Interchange Code: A scheme of assigning characters to each of the 256 possible combinations of 8 bits (1 byte). Several other schemes are also used, such as BCD and ASCII.

Echo or Echoplex

Governs the appearance of characters on your VDT screen. Echo on means that the characters are sent back to the screen by the receiving computer; Echo off means that they are not.

Editor

An interactive program that allows you to input, update, delete and store information on the computer. The information may be programs, data, or actual textual material such as letters or dissertations.

Electronic Form

A text formatting term: The name that Xerox systems uses for a predefined graphic overlay form. The must common use of an overlay at UIC is to print a departmental letterhead. Departments may contact the ACCC to arrange to have a letterhead overlay developed for their departments.

Electronic Mail

A computer system which allows users to exchange messages, notes and files. See the ACCC Email page. See also POP and IMAP.

EIA

Electronic Industries Association: A standards development organization for electrical and functional characteristics of interface equipment.

EPS Encapsulated PostScript File

A file format for describing graphics and page segments for PostScript devices.

Email account

Traditionally, an email account is a computer on which you receive mail and an id that identifies your account on that computer. Maildrop is a newer term that means pretty much the same thing as email account. POP account is also similar, but a bit more specific -- it says that you'll use a POP server to retrieve your incoming mail. (Eudora talks about "your POP account" in its manuals and online helps.)

These days, an email account might be just that -- an account that only gives you a maildrop for incoming mail, without a standard computer account that you can "login to." In the UNIX world, the "login to and do computer-type stuff on" type of account is called a UNIX shell account. An ACCC UNIX account is a UNIX shell account, as well as serving as your maildrop. See the ACCC Accounts page for more information on ACCC accounts and on opening yours.

Email address

has the form "person id" at "domain id." For example, the email address of Ada Byron's account on tigger is adabryon@tigger.cc.uic.edu. In this email address, Ms. Byron is identified by her tigger login id, adabyron, and tigger is identified by its Internet domain name, tigger.cc.uic.edu.

It's tempting to think that the "person id" part of an email address has to be some person's login id on some computer and the "domain id" has to be that computer's Internet domain name. That is often the case, but not always. Consider the perfectly valid email address: consult@uic.edu. "Consult" is neither a person nor a login id. "uic.edu" is a computer, but neither consult nor anyone else who uses a "netid@uic.edu" email address has an account on that computer. See also Netid.

Email program

the program or package that you use to read and reply to, save or delete incoming mail messages, and to send mail messages of your own. Mail programs are called "user agents" in the official descriptions of MIME -- Multipurpose Internet Mail Extensions. (See Making Email Talk in the September/October 1996 issue of The A3C Connection.) The ACCC recommends three email programs -- Eudora (for Windows and the Mac), WebMail (which only needs a Web browser), and Pine (for UNIX).

Emoticon

See Smilie.

Emulation

Using software which makes a PC behave as though it were a terminal, or which alters the characteristics of a user's terminal to act as a different type of terminal.

Encoding

To convert data into a form which is acceptable for some piece of computer equipment or task. See also compression and base64.

Encrypt

To make temporarily unreadable. Datasets can be encrypted to ensure privacy. See the A3C Connection article on encryption at: http://www.uic.edu/depts/accc/newsletter/adn16/encrypt.html

Ethernet

Baseband protocol and technology for the cables and specialized circuitry which is used to physically connect the machines on medium speed (10 Mbps) local networks. Ethernet uses CSMA/CD (Carrier Sense Multiple Access with Collision Detection). In plain English, this means that ethernet is a "broadcast medium", similar to a party line telephone: every machine on a particular Ethernet network looks at the Ethernet address on each packet as it goes by to see if it is for them. When a transmitting data station on an ethernet detects another signal being transmitted (a "collision"), it stops sending, sends a jam signal, and then waits for a variable time before trying again. For more information, see internet.com's PC Webopaedia entry on ethernet. See also Fast Ethernet.

Eudora

Eudora is an email reading program, one of three that are supported by ACCC at UIC. (Pine for UNIX and WebMail for any Web browser are the other two.)

EVL

Electronic Visualization Laboratory at UIC, which advances research in computer graphics and interactive techniques through a unique interdisciplinary blend of engineering, science and art, offering advanced degrees through the UIC Electrical Engineering and Computer Science department and the UIC School of Art and Design.

EXCP

EXecute Channel Program: The execution of a program in the channel (see Channel). The number of EXCP's in a job is generally the number of blocks of data sent or received from input/output devices.

+--+ F +--+

Fast Ethernet

100 Mbps Ethernet, also for LANs.

FDDI

Fiber Distributed Data Interface: An ANSI standard specifying a higher speed (100-Mbps) token-passing network using fiber-optic cable and a dual-ring architecture to provide redundancy.

Fiber-optic cable

A thin, flexible cable which conducts modulated light transmissions. It is more expensive than other types of network cabling, but it is not susceptible to electromagnetic interference and is capable of higher data transmission speeds. The ADN-ii uses fiber-optic cable.

File

A collection of information stored in any of numerous forms on any of numerous devices. A file may contain programs, data, or text. (In the very old days, on MVS, files were called datasets.)

File Identifier or Fileid

The name of file on CMS.

File server

A device holding files which are available to everyone connected to a LAN. The file server's software allows it to provide the machines on the LAN with remote disk drives which function as if they were attached directly to their machine. Examples of file server software are Microsoft's LAN Manager, IBM's LAN Server, and Novell's NetWare.

Finger

A protocol (an on UICVM CMS and on the public personal computers a command) which allows you to get information on people using computer systems on the Internet network.

Fixed Pitch Fonts

A text formatting term: A font in which all the characters have the same width (as in a mechanical typewriter). Also known as "mono-spaced fonts". See also Proportional Fonts.

Flame

A code word in electronic messages indicating a heated argument. Electronic communications lack the clues given by the body or voice in more personal methods of communication, are therefore much more easily misunderstood. See also ":-)".

FLOP

FLoating point OPeration: An operation is a computer action which is specified by a single computer instruction or a high level language statement, and a floating point operation is an operation made on a floating point number. The time used for an average FLOP is a measure of a computer's speed (see Megaflop).

Floppy Disk

A small portable flexible magnetic disk used for data storage on many microcomputers. Floppies come in 3 and a half and 5 and a quarter inch sizes, with several densities and formats.

FM Synthesis

Creating sounds and musical tones by directly manipulating the frequency of the audio signal.

Folio

A text formatting term: The lines at the top or bottom of a page that contain the page number, publication name, publication data, volume numbers, and so on.

Font

A text formatting term: A complete assortment of printer characters in a particular type style, typeface, size and orientation. Most fonts include letters, numbers, punctuation and some special symbols. Note that the Roman (normal), Italic, Bold and BoldItalic typeface forms of any type style and size are each separate fonts.

A font family is a complete set of characters in the same type style, including all sizes and typefaces, such as bold, italic, underline, et cetera.

Footer

A text formatting term: One or more lines of text that appear at the bottom of every page.

Foreground

The interactive portion of the a computer system; e.g. when you are using CMS interactively, your commands are executed in the foreground, when you issue them.

FORTRAN

FORmula TRANslating language: An old but still very common programming language used in the scientific field. FORTRAN was the first high-level language to become widely used. See Programming Languages at the ACCC.

FTP

File Transfer Protocol: A protocol in the Internet suite which allows a user on any computer to get files from another computer, or to send files to another computer. FTP is used for file transfer on the ADN-ii network. See A Quick Introduction to FTP. See also TCP/IP.

Full Screen

This term refers to the ability of a system to manipulate and edit the text on the screen as a whole, as opposed to one line at a time.

Full duplex

A method of communication between two computers (or devices) that enables simultaneous transmission in both directions.

+--+ G +--+

Gateway

A protocol translating device (software and hardware) used to pass information from one network, with its set of protocols, to another network, which may have a different set of protocols. In computer networks, gateways refer to sites which belong to two or more networks allowing data to "cross over" from one network to another. See also Bridge.

Generic Font

A text formatting term: A representation of alpha-numeric characters on a screen that may not reflect what the final characters will look like. Utilities that allow the viewing of printer formatted text on your screen generally use generic fonts.

GIF Graphics Interchange Format

A color image transfer protocol developed by CompuServe.

Gigabit Ethernet

The newest version of Ethernet, which supports data transfer rates of one gigabit (1,000 megabits) per second.

GML

Waterloo Generalized Markup Language, GML, a text formatting package that was on CMS.

Gopher

Internet Gopher is a set of client-server protocols which provides a distributed information delivery system around which a world/campus-wide information system (CWIS) can readily be constructed. Most World Wide Web browsers support Gopher, but it is rarely used any more.

GPSS

General Purpose Simulation System: A powerful general purpose simulator which provides a wide range of capacities for discrete system modeling.

Graphics

A generic term used to describe the pictorial representation of data. Graphic devices include printers, plotters, or special terminals.

+--+ H +--+

Half duplex

A method of communication between two computers (or devices) that allows transmission in only one direction at a time.

Handshaking

An exchange of predetermined signals between two computers or between a computer and a peripheral device such as a modem or a printer. Handshaking allows the computer to ascertain whether another device is present and ready to transmit or receive data.

Hard copy

Usually hard copy means paper, but presumably can mean any printed computer output, such as microfilm.

Hardware

The physical devices that make up a computer system.

Hard disk

A magnetic disk storage device used on larger microcomputers. Hard disks are similar to the disk storage on mainframes, and are permanently installed in the micro.

Header

(1) A text formatting term: One or more lines of text that appear at the top of every page of a document. (2) A computer communications term: Control information which is added before data when it is encapsulated for network transmission.

HELP

An online system of information about various commands and programs, available on all of our mainframe interactive systems, and also internally in many interactive software packages.

Host

A computer which is used for general computing purposes, which is also connected to a network.

HSM

Hierarchical Storage Manager: The automatic archiving system used on MVS at the ACCC.

 

HTML:

HyperText Markup Language, the lingua franca of the WWW. A particular instance of an SGML markup language, particularly suitable for using hypertext pointers. For more information, see the Inform Internet and the WWW menu.

HTTP:

HyperText Transport Protocol. The rules by which WWW browsers and servers communicate.

HTTPD:

HTTP Daemon, the server side of the WWW client/server equation.

Hub

Generally, a device which serves as the center of a star shaped network. In Ethernet/IEEE 802.3 networks, a hub is an Ethernet multiport repeater (a concentrator).

Hypermedia

Nonlinear multimedia, with hypertext navigational links, nodes, and controls.

Hyphenation

A text formatting term: Breaking up words at syllables or other natural dividing points so that the lines of text are properly balanced. Hyphenation can be achieved in several ways: some programs let you manually insert discretionary hyphens which are only visible when they fall at the end of a line of text, some programs insert hyphens automatically based on a dictionary of words, and some programs use a logic formula or algorithm to hyphenate words.