E

E

e n. The symbol for the base of the natural logarithm 2.71828. Introduced by Leonhard Euler in the mid-eighteenth century, e is a fundamental mathematical constant used in calculus, science, engineering, and programming languages, as in logarithmic and exponential functions in C and Basic.

e- prefix Short for electronic. A prefix indicating that a word refers to the computer-based version of some traditionally nonelectronic term, as e-mail, e-commerce, and e-money.

E- prefix See exa-.

E3 n. Acronym for Electronic Entertainment Expo. A major convention where game industry developers, manufacturers, and publishers demonstrate their latest wares.

EAI n. Acronym for Enterprise Application Integration. The process of coordinating the operation of the various programs, databases, and existing technologies of a business or enterprise so that they function as an efficient, business-wide system.

early binding n. See static binding.

EAROM n. Acronym for electrically alterable read-only memory. See EEPROM.

Easter egg n. A hidden feature of a computer program. It may be a hidden command, an animation, a humorous message, or a list of credits for the people who developed the program. In order to display an Easter egg, a user often must enter an obscure series of keystrokes.

eavesdropper n. See lurker.

EBCDIC n. Acronym for Extended Binary Coded Decimal Interchange Code. An IBM code that uses 8 bits to represent 256 possible characters, including text, numbers, punctuation marks, and transmission control characters. It is used primarily in IBM mainframes and minicomputers. Compare ASCII.

e-bomb n. Short for e-mail bomb. A technique used by some hackers in which a target is put on a large number of mailing lists so that network traffic and storage are tied up by e-mail sent by other mailing list subscribers to the lists recipients.

e-book n. Format allowing books and other large texts to be downloaded from a Web site and viewed digitally. Typically, reading an e-book requires using a small computer appliance that is about the size of a paperback book and consists of a display screen and basic controls. Users can bookmark, highlight, or annotate text, but rights management features may prevent users from e-mailing, printing, or otherwise sharing e-book contents. Also called: electronic book.

e-cash n. See e-money.

ECC n. See error-correction coding.

echo¹ n. In communications, a signal transmitted back to the sender that is distinct from the original signal. Network connections can be tested by sending an echo back to the main computer.

echo² vb. To transmit a received signal back to the sender. Computer programs, such as MS-DOS and OS/2, can be commanded to echo input by displaying data on the screen as it is received from the keyboard. Data communications circuits may echo text back to the originating terminal to confirm that it has been received.

echo cancellation n. A technique for eliminating unwanted incoming transmissions in a modem that are echoes of the modem s own transmission. The modem sends a modified, reversed version of its transmission on its receiving path, thus erasing echoes while leaving incoming data intact. Echo cancellation is standard in V.32 modems.

echo check n. In communications, a method for verifying the accuracy of transmitted data by retransmitting it to the sender, which compares the echoed signal with the original.

echo loop attack n. A form of denial of service (DoS) attack in which a connection is established between User Datagram Protocol (UDP) services on two or more host machines that bounce an increasing volume of packets back and forth. The echo loop attack ties up the host machines and causes network congestion.

echoplex n. In communications, a technique for error detection. The receiving station retransmits data back to the sender s screen, where it can be displayed visually to check for accuracy.

echo suppressor n. In communications, a method for preventing echoes in telephone lines. Echo suppressors inhibit signals from the listener to the speaker, creating a one-way channel. For modems that send and receive on the same frequency, the echo suppressor must be disabled to allow two-way transmission. This disabling produces the high-pitched tone heard in modem-to-modem connections.

ECL n. See emitter-coupled logic.

ECMA n. Acronym for European Computer Manufacturers Association. An organization based in Geneva, Switzerland, whose American counterpart is CBEMA (Computer and Business Equipment Manufacturers Association). Its standard, ECMA-101, is used for transmitting formatted text and graphical images while retaining their original formatting.

ECMAScript n. A standardized, object-oriented scripting language specification defined by the European Computer Manufacturers Association (ECMA) 262 specification. This language was originally designed to perform computations and manipulate objects within a Web environment. Microsoft implements ECMAScript as JScript, and Netscape implements ECMAScript as JavaScript.

ECML n. See Electronic Commerce Modeling Language.

e-commerce n. Short for electronic commerce. Commercial activity that takes place by means of computers connected through a network. Electronic commerce can occur between a user and a vendor through the Internet, an online information service, or a bulletin board system (BBS), or between vendor and customer computers through electronic data interchange (EDI). Also called: e-tail. See also EDI.

ECP n. Acronym for Enhanced Capabilities Port. A protocol, developed by Microsoft and Hewlett Packard, for bidirectional, high-speed communication between a computer and a printer or scanner. ECP is part of the IEEE 1284 standard, which specifies enhanced parallel ports that are compatible with the older, de facto standard Centronics parallel ports. See also EPP, IEEE 1284.

e-credit n. See electronic credit.

e-currency n. See e-money.

edge n. 1. In graphics, a border joining two polygons. 2. In data structures, a link between two nodes on a tree or graph. See also graph, node (definition 3), tree.

EDGE n. Acronym for Enhanced Data Rates for Global Evolution or Enhanced Data Rates for GSM and TDMA Evolution. A third-generation enhancement to the Global System for Mobile Communications (GSM) wireless service, which allows data, multimedia services, and applications to be delivered on broadband at rates up to 384 Kbps.

edge connector n. The set of wide, flat, metallic contacts on an expansion board that is inserted into a personal computer s expansion slot or a ribbon cable s connector. It connects the board with the system s shared data pathway, or bus, by means of a series of printed lines that connect to the circuits on the board. The number and pattern of lines differ with the various types of connectors. See also expansion board, ribbon cable.

EDI n. Acronym for Electronic Data Interchange. A standard for exchanging bundles of data between two companies via telephone lines or the Internet. EDI transmits much larger bundles of data than can be transmitted via e-mail. For EDI to be effective, users must agree on certain standards for formatting and exchanging information, such as the X.400 protocol. See also CCITT X series, standard (definition 1).

edit¹ n. A change made to a file or a document.

edit² vb. 1. To make a change to an existing file or document. Changes to the existing document are saved in memory or in a temporary file but are not added to the document until the program is instructed to save them. Editing programs typically provide safeguards against inadvertent changes, such as by requesting confirmation before saving under an existing filename, by allowing the user to assign a password to a file, or by giving the option of setting the file to read-only status. 2. To run software that makes extensive, predictable changes to a file automatically, such as a linker or a filter for graphics.

editing keys n. A set of keys on some keyboards that assists in editing. Located between the main keyboard and the numeric keypad, editing keys consist of three pairs: Insert and Delete, Home and End, and Page Up and Page Down.

edit key n. In a software application, a predefined key or combination of keys that, when pressed, causes the application to enter edit mode.

edit mode n. The mode of a program in which a user can make changes to a document, as by inserting or deleting data or text. Compare command mode.

editor n. A program that creates files or makes changes to existing files. An editor is usually less powerful than a word processor, lacking the latter s capability for text formatting, such as use of italics. Text or full-screen editors allow the user to move through the document using direction arrows. In contrast, line editors require the user to indicate the line number on which text is to be edited. See also Edlin.

Edlin n. An outdated line-by-line text editor used in MS-DOS through version 5. Its OS/2 counterpart is SSE. See also editor.

EDMS n. Acronym for electronic document management system. See document management system.

EDO DRAM n. Acronym for extended data out dynamic random access memory. A type of memory that allows for faster read times than DRAM of comparable speed by allowing a new read cycle to begin while data is being read from a previous cycle. This allows for faster overall system performance. Compare dynamic RAM, EDO RAM.

EDO RAM n. Acronym for extended data out random access memory. A type of dynamic RAM that keeps data available for the CPU while the next memory access is being initialized, resulting in increased speed. Pentium-class computers using Intel s Triton chip set are designed to take advantage of EDO RAM. See also central processing unit, dynamic RAM. Compare EDO DRAM.

EDP n. 1. Acronym for electronic data processing. See data processing. 2. Acronym for Enhanced Capabilities Port. A protocol, developed by Microsoft and Hewlett Packard, for bidirectional, high-speed communication between a computer and a printer or scanner. ECP is part of the IEEE 1284 standard, which specifies enhanced parallel ports that are compatible with the older, de facto standard Centronics parallel ports. See also EPP, IEEE 1284.

.edu n. In the Internet s Domain Name System, the top-level domain that identifies addresses operated by four-year, degreed educational institutions. The domain name .edu appears as a suffix at the end of the address. In the United States, schools that offer kindergarten through high school classes use the top-level domain of .k12.us or just .us. See also DNS (definition 1), domain (definition 3), .k12.us, .us. Compare .com, .gov, .mil, .net, .org.

edutainment n. Multimedia content in software, on CD-ROM, or on a Web site that purports to educate the user as well as entertain. See also multimedia.

EEMS n. Acronym for Enhanced Expanded Memory Specification. A superset of the original Expanded Memory Specification (EMS). Version 3.0 of EMS allowed only storage of data and supported 4-page frames. EEMS allowed up to 64 pages along with executable code to be stored in expanded memory. The features of EEMS were included in EMS version 4.0. See also EMS, page frame.

EEPROM n. Acronym for electrically erasable programmable read-only memory. A type of EPROM that can be erased with an electrical signal. It is useful for stable storage for long periods without electricity while still allowing reprogramming. EEPROMs contain less memory than RAM, take longer to reprogram, and can be reprogrammed only a limited number of times before wearing out. See also EPROM, ROM.

EFF n. See Electronic Frontier Foundation.

e-form n. Short for electronic form. An online document that contains blank spaces for a user to fill in with requested information and that can be submitted through a network to the organization requesting the information. On the Web, e-forms are often coded in CGI script and secured via encryption. See also CGI (definition 1).

EGA n. Acronym for Enhanced Graphics Adapter. An IBM video display standard introduced in 1984. It emulates the Color/Graphics Adapter (CGA) and the Monochrome Display Adapter (MDA) and provides medium-resolution text and graphics. It was superseded by Video Graphics Display (VGA).

ego-surfing n. The practice of using a Web search engine to search for one s own name on the Internet.

EGP n. See exterior gateway protocol.

e-home n. See smart home.

EIA n. Acronym for Electronic Industries Association. An association based in Washington, D.C., with members from various electronics manufacturers. It sets standards for electronic components. RS-232-C, for example, is the EIA standard for connecting serial components. See also RS-232-C standard.

EIDE or E-IDE n. Acronym for Enhanced Integrated Drive Electronics. An extension of the IDE standard, EIDE is a hardware interface standard for disk drive designs that house control circuits in the drives themselves. It allows for standardized interfaces to the system bus while providing for advanced features, such as burst data transfer and direct data access. EIDE accommodates drives as large as 8.4 gigabytes (IDE supports up to 528 megabytes). It supports the ATA-2 interface, which permits transfer rates up to 13.3 megabytes per second (IDE permits up to 3.3 megabytes per second), and the ATAPI interface, which connects drives for CD-ROMs, optical discs and tapes, and multiple channels. Most PCs have EIDE drives, which are cheaper than SCSI drives and provide much of the same functionality. See also IDE, SCSI.

Eiffel n. An advanced object-oriented programming language with a syntax similar to C, developed by Bertrand Meyer in 1988. Eiffel runs on MS-DOS, OS/2, and UNIX. Its major design features are the ability to use modules in multiple programs and software extensibility.

Eiffel# n. Pronounced Eiffel Sharp. A subset language of Eiffel specifically designed to target the .NET Framework and embody the full extent of Design by Contract. See also Design by Contract.

eight dot three n. See 8.3.

EIP n. See enterprise information portal.

EIS n. See executive information system.

EISA n. Acronym for Extended Industry Standard Architecture. A bus standard for the connection of add-on cards to a PC motherboard, such as video cards, internal modems, sound cards, drive controllers, and cards that support other peripherals. EISA was introduced in 1988 by a consortium of nine computer industry companies. The companies AST Research, Compaq, Epson, Hewlett-Packard, NEC, Olivetti, Tandy, Wyse, and Zenith were referred to collectively as the Gang of Nine. EISA maintains compatibility with the earlier Industry Standard Architecture (ISA) but provides for additional features introduced by IBM in its Micro Channel Architecture bus standard. EISA has a 32-bit data path, and it uses connectors that can accept ISA cards. However, EISA cards are compatible only with EISA systems. EISA can operate at much higher frequencies than the ISA bus and provides much faster data throughput than ISA. See also ISA, Micro Channel Architecture.

EJB n. See Enterprise JavaBeans.

electroluminescent adj. Giving off light when electric current is applied. Electroluminescent panels are used in portable computers to backlight the liquid crystal displays. A thin phosphor layer is sandwiched between two thin electrode panels, one of which is nearly transparent. See also liquid crystal display.

electroluminescent display n. A type of flat-panel display used in laptops in which a thin phosphor layer is set between vertical and horizontal electrodes. These electrodes form xy-coordinates; when a vertical and a horizontal electrode are charged, the phosphor at their intersection emits light. Electroluminescent displays provide a sharp, clear image and a wide viewing angle. They were replaced by active matrix LCD screens. See also flat-panel display, liquid crystal display, passive-matrix display. Compare active-matrix display.

electrolysis n. A process in which a chemical compound is broken down into its constituent parts by passing an electric current through it.

electromagnet n. A device that creates a magnetic field when electric current passes through it. An electromagnet typically contains an iron or steel core with wire wrapped around it. Current is passed through the wire, producing a magnetic field. Electromagnets are used in disk drives to record data onto the disk surface.

electromagnetic radiation n. The propagation of a magnetic field through space. Radio waves, light, and X rays are examples of electromagnetic radiation, all traveling at the speed of light.

electromagnetic spectrum n. The range of frequencies of electromagnetic radiation. In theory, the spectrum s range is infinite. See the illustration.

Electromagnetic spectrum.

electromotive force n. The force that causes movement in charge carriers (the electrons) in a conductor. Acronym: EMF. Also called: potential, voltage. See also ampere, coulomb.

electron beam n. A stream of electrons moving in one direction. An electron beam is used in a cathode-ray tube (CRT) to produce an image as it is passed across the phosphor coating inside the tube. See also CRT.

electron gun n. A device that produces an electron beam, typically found in television or computer monitors. See also CRT.

electronic bulletin board n. See BBS (definition 1).

electronic cash n. See e-money.

electronic circuit n. See circuit.

electronic commerce n. See e-commerce.

Electronic Commerce Modeling Language n. A computer language developed by leading e-commerce companies as a standard for inputting e-wallet information into the payment fields of Web sites. This allows for one-click transfer of e-wallet information at compatible Web sites. Acronym: ECML.

electronic credit n. A form of electronic commerce involving credit card transactions carried out over the Internet. Also called: e-credit. See also e-commerce.

electronic data interchange n. See EDI.

electronic data processing n. See data processing.

electronic form n. See e-form.

Electronic Frontier Foundation n. A public advocacy organization dedicated to the defense of civil liberties for computer users. The organization was founded in 1990 by Mitchell Kapor and John Perry Barlow as a response to U.S. Secret Service raids on hackers. Acronym: EFF.

electronic funds transfer n. The transfer of money via automated teller machine, telephone lines, or Internet connection. Examples of electronic fund transfers include using a credit card to make purchases from an e-commerce site, or using an automated teller machine or automated telephone banking system to move funds between bank accounts. Acronym: EFT.

Electronic Industries Association n. See EIA.

electronic journal n. See journal.

electronic mail n. See e-mail¹.

electronic mail services n. Services that allow users, administrators, or daemons to send, receive, and process e-mail. See also daemon.

electronic mall n. A virtual collection of online businesses that affiliate with the intention of increasing the exposure of each business through the fellow businesses.

electronic money n. See e-money.

electronic music n. Music created with computers and electronic devices. See also MIDI, synthesizer.

electronic office n. A term used especially in the late 1970s to mid-1980s to refer to a hypothetical paperless work environment to be brought about by the use of computers and communications devices.

electronic paper n. Technology allowing a computer display to imitate the look and feel of traditional paper media. Electronic paper consists of thin, flexible sheets of plastic containing millions of small beads called microcapsules. Each microcapsule contains both a black and a white pigment and displays the proper color in response to an electrical charge. It retains this pattern until a new screen of text or images is requested.

electronic photography n. See digital photography.

Electronic Privacy Information Center n. See EPIC.

electronic publishing n. A general term for distributing information via electronic media, such as communications networks or CD-ROM.

electronics n. The branch of physics dealing with electrons, electronic devices, and electrical circuits.

Electronics Industries Association n. See EIA.

electronic software distribution n. A means of directly distributing software to users on line over the Internet. Electronic software distribution is analogous to direct-mail ordering. Acronym: ESD.

electronic spreadsheet n. See spreadsheet program.

electronic storefront n. A business that displays its merchandise on the Internet and has provisions for contact or online sales.

electronic text n. See e-text.

electron tube n. A device for switching and amplifying electronic signals. It consists of a sealed glass container with electronic elements, such as metallic plates and grids, inside. In most applications, tubes have been replaced by transistors, although they are still used in cathode-ray tubes and in some radio frequency circuits and audio amplifiers. Also called: vacuum tube, valve. See also CRT.

electrophotographic printers n. Printers in a category including laser, LED, LCD, and ion-deposition printers. In such a printer, a negative image is applied to an electrically charged, photosensitive drum. A photosensitive drum develops a pattern of electrostatic charge on its surface representing the photo negative of the image the drum will print. Powdered ink (toner) adheres to the charged areas of the drum, the drum presses the ink onto the paper, and then heat binds the toner to the paper. The printer types vary mainly in how they charge the drum. See also ion-deposition printer, laser printer, LCD printer, LED printer.

electrophotography n. The production of photographic images using electrostatic charges. This method is used in photocopiers and laser printers. Also called: xerography. See also electrophotographic printers.

electroplating n. The use of electrolysis for depositing a thin layer of one material onto another material. See also electrolysis.

electrostatic adj. Of or relating to electric charges that are not flowing along a conducting path. Electrostatic charges are used in copiers and laser printers to hold toner particles on a photoconducting drum and in flatbed plotters to hold the plot medium in place.

electrostatic discharge n. The discharge of static electricity from an outside source, such as human hands, into an integrated circuit, often resulting in damage to the circuit. Acronym: ESD.

electrostatic plotter n. A plotter that creates an image from a dot pattern on specially coated paper. The paper is electrostatically charged and exposed to toner, which adheres to the dots. Electrostatic plotters can be up to 50 times faster than pen plotters but are more costly. Color models produce images through multiple passes with cyan, magenta, yellow, and black. See also plotter. Compare electrophotographic printers, pen plotter.

electrostatic printer n. See electrostatic plotter.

elegant adj. Combining simplicity, terseness, efficiency, and subtlety. On the academic side of computer science, elegant design (say, of programs, algorithms, or hardware) is a priority, but in the frenetic pace of the computer industry, elegant design may be sacrificed for the sake of speeding a product s development, sometimes resulting in bugs that are difficult to correct.

element n. 1. Any stand-alone item within a broader context. For example, a data element is an item of data with the characteristics or properties of a larger set; a picture element (pixel) is one single dot on a computer screen or in a computer graphic; a print element is the part of a daisy-wheel printer that contains the embossed characters. See also daisy-wheel printer, data element, graphics primitive, pixel, thimble. 2. In markup languages such as HTML and SGML, the combination of a set of tags, any content contained between the tags, and any attributes the tags may have. Elements can be nested, one within the other. See also attribute (definition 3), HTML, markup language, SGML.

elevator n. The square box within a scroll bar that can be moved up and down to change the position of text or an image on the screen. See the illustration. Also called: scroll box, thumb. See also scroll bar.

Elevator.

elevator seeking n. A method of limiting hard disk access time in which multiple requests for data are prioritized based on the location of the data relative to the read/write head. This serves to minimize head movement. See also access time (definition 2), hard disk, read/write head.

elite n. 1. A size of fixed-width type that prints 12 characters to the inch. 2. A fixed-width font that may be available in various type sizes. See also monospace font.

ELIZA n. A program, modeled on Rogerian psychotherapy, that conducts simulated conversations with humans by echoing responses and posing questions based on key words in earlier comments. It was created by Dr. Joseph Weizenbaum, who considered it a bit of a joke and was alarmed that people took it seriously. See also artificial intelligence, Turing test.

ellipsis n. A set of three dots (...) used to convey incompleteness. In many windowing applications, selection of a command that is followed by an ellipsis will produce a submenu or a dialog box. In programming and software manuals, an ellipsis in a syntax line indicates the repetition of certain elements. See also dialog box, syntax.

elm n. Short for electronic mail. A program for reading and composing e-mail on UNIX systems. The elm program has a full-screen editor, making it easier to use than the original mail program, but elm has largely been superseded by pine. See also e-mail¹. Compare Eudora, pine.

e-mail¹ or email or E-mail n. 1. Short for electronic mail. The exchange of text messages and computer files over a communications network, such as a local area network or the Internet, usually between computers or terminals. 2. An electronic text message.

e-mail² or email or E-mail vb. To send an e-mail message.

e-mail address n. A string that identifies a user so that the user can receive Internet e-mail. An e-mail address typically consists of a name that identifies the user to the mail server, followed by an at sign (@) and the host name and domain name of the mail server. For example, if Anne E. Oldhacker has an account on the machine called baz at Foo Enterprises, she might have an e-mail address [e-mail], which would be pronounced A E O at baz dot foo dot com.

e-mail filter n. A feature in e-mail-reading software that automatically sorts incoming mail into different folders or mailboxes based on information contained in the message. For example, all incoming mail from a user s Uncle Joe might be placed in a folder labeled Uncle Joe. Filters may also be used either to block or accept e-mail from designated sources.

e-mail management system n. An automated e-mail response system used by an Internet-based business to sort incoming e-mail messages into predetermined categories and either reply to the sender with an appropriate response or direct the e-mail to a customer service representative. Acronym: EMS.

embed vb. To insert information created in one program, such as a chart or an equation, into another program. After the object is embedded, the information becomes part of the document. Any changes made to the object are reflected in the document.

embedded adj. In software, pertaining to code or a command that is built into its carrier. For example, application programs insert embedded printing commands into a document to control printing and formatting. Low-level assembly language is embedded in higher-level languages, such as C, to provide more capabilities or better efficiency.

embedded chip n. See embedded system.

embedded command n. A command placed in a text, graphics, or other document file, often used for printing or page-layout instructions. Such commands often do not appear on screen but can be displayed if needed. In transferring documents from one program to another, embedded commands can cause problems if the programs are incompatible.

embedded controller n. A processor-based controller circuit board that is built into the computer machinery. See also controller.

embedded hyperlink n. A link to a resource that is embedded within text or is associated with an image or an image map. See also hyperlink, image map.

embedded interface n. An interface built into a hardware device s drive and controller board so that the device can be directly connected to the computer s system bus. See also controller, interface (definition 3). Compare ESDI, SCSI, ST506 interface.

embedded system n. Microprocessors used to control devices such as appliances, automobiles, and machines used in business and manufacturing. An embedded system is created to manage a limited number of specific tasks within a larger device or system. An embedded system is often built onto a single chip or board and is used to control or monitor the host device usually with little or no human intervention and often in real time. See also microprocessor.

em dash n. A punctuation mark ( ) used to indicate a break or interruption in a sentence. It is named for the em, a typographical unit of measure that in some fonts equals the width of a capital M. Compare en dash, hyphen.

EMF n. See electromotive force.

emitter n. In transistors, the region that serves as a source of charge carriers. Compare base (definition 3), collector.

emitter-coupled logic n. A circuit design in which the emitters of two transistors are connected to a resistor so that only one of the transistors switches at a time. The advantage of this design is very high switching speed. Its drawbacks are the high number of components required and susceptibility to noise. Acronym: ECL.

EMM n. See Expanded Memory Manager.

e-money or emoney n. Short for electronic money. A generic name for the exchange of money through the Internet. Also called: cybercash, digicash, digital cash, e-cash, e-currency.

emotag n. In an e-mail message or newsgroup article, a letter, word, or phrase that is encased in angle brackets and that, like an emoticon, indicates the attitude the writer takes toward what he or she has written. Often emotags have opening and closing tags, similar to HTML tags, that enclose a phrase or one or more sentences. For example: <joke>You didn t think there would really be a joke here, did you?</joke>. Some emotags consist of a single tag, such as <grin>. See also emoticon, HTML.

emoticon n. A string of text characters that, when viewed sideways, form a face expressing a particular emotion. An emoticon is often used in an e-mail message or newsgroup post as a comment on the text that precedes it. Common emoticons include :-) or :) (meaning I m smiling at the joke here ), ;-) ( I m winking and grinning at the joke here ), :-( ( I m sad about this ), :-7 ( I m speaking with tongue in cheek ), :D or :-D (big smile; I m overjoyed ), and :-O (either a yawn of boredom or a mouth open in amazement). Compare emotag.

EMS n. Acronym for Expanded Memory Specification. A technique for adding memory to PCs that allows for increasing memory beyond the Intel 80x86 microprocessor real-mode limit of 1 megabyte (MB). In earlier versions of microprocessors, EMS bypassed this memory board limit with a number of 16-kilobyte banks of RAM that could be accessed by software. In later versions of Intel microprocessors, including the 80386 and 80486 models, EMS is converted from extended memory by software memory managers, such as EMM386 in MS-DOS 5. Now EMS is used mainly for older MS-DOS applications because Windows and other applications running in protected mode on 80386 and higher microprocessors are free of the 1-MB limit. Also called: LIM EMS. See also expanded memory, protected mode. Compare conventional memory, extended memory.

em space n. A typographical unit of measure that is equal in width to the point size of a particular font. For many fonts, this is equal to the width of a capital M, from which the em space takes its name. Compare en space, fixed space, thin space.

emulate vb. For a hardware or software system to behave in the same manner as another hardware or software system. In a network, for example, microcomputers might emulate terminals in order to communicate with mainframes.

emulation n. The process of a computer, device, or program imitating the function of another computer, device, or program.

emulator n. Hardware or software designed to make one type of computer or component act as if it were another. By means of an emulator, a computer can run software written for another machine. In a network, microcomputers might emulate terminals in order to communicate with mainframes.

emulsion laser storage n. A method for recording data in film by selective heating with a laser beam.

enable vb. To activate or turn on. Compare disable.

encapsulate vb. 1. To treat a collection of structured information as a whole without affecting or taking notice of its internal structure. In communications, a message or packet constructed according to one protocol, such as a TCP/IP packet, may be taken with its formatting data as an undifferentiated stream of bits that is then broken up and packaged according to a lower-level protocol (for example, as ATM packets) to be sent over a particular network; at the destination, the lower-level packets are assembled, re-creating the message as formatted for the encapsulated protocol. See also ATM (definition 1). 2. In object-oriented programming, to keep the implementation details of a class a separate file whose contents do not need to be known by a programmer using that class. See also object-oriented programming, TCP/IP.

Encapsulated PostScript n. See EPS.

encapsulated type n. See abstract data type.

encapsulation n. 1. In object-oriented programming, the packaging of attributes (properties) and functionality (methods or behaviors) to create an object that is essentially a black box one whose internal structure remains private and whose services can be accessed by other objects only through messages passed via a clearly defined interface (the programming equivalent of a mailbox or telephone line). Encapsulation ensures that the object providing service can prevent other objects from manipulating its data or procedures directly, and it enables the object requesting service to ignore the details of how that service is provided. See also information hiding. 2. In terms of the Year 2000 problem, a method of dealing with dates that entails shifting either program logic (data encapsulation) or input (program encapsulation) backward into the past, to a parallel year that allows the system to avoid Year 2000 complications. Encapsulation thus allows processing to take place in a time warp created by shifting to an earlier time before processing and for accuracy shifting output forward by the same number of years to reflect the actual date. See data encapsulation, program encapsulation.

encipher vb. See encrypt.

encode vb. 1. See encrypt. 2. In programming, to put something into code, which frequently involves changing the form for example, changing a decimal number to binary-coded form. See also binary-coded decimal, EBCDIC.

encoder n. 1. In general, any hardware or software that encodes information that is, converts the information to a particular form or format. For example, the Windows Media Encoder converts audio and video to a form that can be streamed to clients over a network. 2. In reference to MP3 digital audio in particular, technology that converts a WAV audio file into an MP3 file. An MP3 encoder compresses a sound file to a much smaller size, about one-twelfth as large as the original, without a perceptible drop in quality. Also called: MP3 encoder. See also MP3, WAV. Compare rip, ripper.

encoding n. 1. See Huffman coding. 2. A method of dealing with computers with Year 2000 problems that entails storing a four-digit year in date fields designed to hold only two digits in a program or system. This can be accomplished by using the bits associated with the date field more efficiently for example, by converting the date field from ASCII to binary or from decimal to hexadecimal, both of which allow storage of larger values.

encrypt vb. To encode (scramble) information in such a way that it is unreadable to all but those individuals possessing the key to the code. Encrypted information is known as cipher text. Also called: encipher, encode.

encryption n. The process of encoding data to prevent unauthorized access, especially during transmission. Encryption is usually based on one or more keys, or codes, that are essential for decoding, or returning the data to readable form. The U.S. National Bureau of Standards created a complex encryption standard, Data Encryption Standard (DES), which is based on a 56-bit variable that provides for more than 70 quadrillion unique keys to encrypt documents. See also DES.

encryption key n. A sequence of data that is used to encrypt other data and that, consequently, must be used for the data s decryption. See also decryption, encryption.

end-around carry n. A special type of end-around shift operation on a binary value that treats the carry bit as an extra bit; that is, the carry bit is moved from one end of the value to the other. See also carry, end-around shift, shift.

end-around shift n. An operation performed on a binary value in which a bit is shifted out of one end and into the other end. For example, a right-end shift on the value 00101001 yields 10010100. See also shift.

en dash n. A punctuation mark ( ) used to show ranges of dates and numbers, as in 1990 92, and in compound adjectives where one part is hyphenated or consists of two words, as in pre Civil War. The en dash is named after a typographical unit of measure, the en space, which is half the width of an em space. See also em space. Compare em dash, hyphen.

End key n. A cursor-control key that moves the cursor to a certain position, usually to the end of a line, the end of a screen, or the end of a file, depending on the program. See the illustration.

End key.

endless loop n. See infinite loop.

end mark n. A symbol that designates the end of some entity, such as a file or word processing document.

end-of-file n. 1. A code placed by a program after the last byte of a file to tell the computer s operating system that no additional data follows. In ASCII, end-of-file is represented by the decimal value 26 (hexadecimal 1A) or the Ctrl+Z control character. Acronym: EOF. 2. An indicator of some sort in a computer program or database that indicates that the end of a file has been reached. If older systems that have the capacity to store only two-digit years in the date field also use end-of-file markers such as 99, they can be susceptible to date-related problems. See also 99 or 9999.

end-of-text n. In data transmission, a character used to mark the end of a text file. End-of-text does not necessarily signify the end of transmission; other information, such as error-checking or transmission control characters, can be included at the end of the file. In ASCII, end-of-text is represented by the decimal value 3 (hexadecimal 03). Acronym: ETX.

end-of-transmission n. A character representing the end of a transmission. In ASCII, the end-of-transmission character has the decimal value 4 (hexadecimal 04). Acronym: EOT.

endpoint n. The beginning or end of a line segment.

end-to-end delivery n. A communications process in networks in which packets are delivered and then acknowledged by the receiving system.

end-to-end examination n. An inspection of all of the processes and systems in place at an organization that affect the computer systems. The examination begins with the data or information that flows into the system, continues with how the data is manipulated and stored, and ends with how the data is output. For example, end-to-end examination is one technique that was employed to ferret out Year 2000 problems in computer systems of an organization.

end user n. The ultimate user of a computer or computer application in its finished, marketable form.

End-User License Agreement n. A legal agreement between a software manufacturer and the software s purchaser with regard to terms of distribution, resale, and restricted use. Acronym: EULA.

Energy Star n. A symbol affixed to systems and components that denotes lower power-consumption design. Energy Star is the name of an Environmental Protection Agency program that encourages PC manufacturers to build systems that are energy efficient. Requirements dictate that systems or monitors be capable of automatically entering a sleep state or lower power-consumption state while the unit is inactive, where the low-power state is defined as 30 watts or less. Systems and monitors that comply with these guidelines are marked with an Energy Star sticker.

engine n. A processor or portion of a program that determines how the program manages and manipulates data. The term engine is most often used in relation to a specific use; for example, a database engine contains the tools for manipulating a database, and a Web search engine has the ability to search World Wide Web indexes for matches to one or more key words entered by the user. Compare back-end processor, front-end processor.

Enhanced Capabilities Port n. See ECP.

enhanced Category 5 cable n. See Cat 5e cable.

Enhanced Data Rates for Global Evolution n. See EDGE.

Enhanced Data Rates for GSM and TDMA Evolution n. See EDGE.

Enhanced Expanded Memory Specification n. See EEMS.

Enhanced Graphics Adapter n. See EGA.

Enhanced Graphics Display n. A PC video display capable of producing graphic images with resolutions ranging from 320 x 200 through 640 x 400 pixels, in color or in black and white. Resolution and color depth depend on the vertical and horizontal scanning frequencies of the display, the capabilities of the video display controller card, and available video RAM.

Enhanced IDE n. See EIDE.

Enhanced Integrated Device Electronics n. See EIDE.

enhanced keyboard n. An IBM 101/102-key keyboard that replaced the PC and AT keyboards. It features 12 function keys across the top (rather than 10 on the left side), extra Control and Alt keys, and a bank of cursor and editing keys between the main keyboard and number pad. It is similar to the Apple Extended Keyboard.

Enhanced Parallel Port n. See EPP.

enhanced serial port n. A connection port for peripheral devices, commonly used for mice and external modems. Enhanced serial ports utilize 16550-type or newer high-speed UART circuits for faster data throughput. Enhanced serial ports are capable of transferring data at speeds as high as 921.6 Kbps. Acronym: ESP. See also input/output port, UART.

Enhanced Small Device Interface n. See ESDI.

ENIAC n. An 1800-square-foot, 30-ton computer containing about 18,000 vacuum tubes and 6000 manual switches. Developed between 1942 and 1946 for the U.S. Army by J. Presper Eckert and John Mauchly at the University of Pennsylvania, ENIAC is considered to have been the first truly electronic computer. It remained in operation until 1955.

enlarge vb. In Windows and other graphical user interfaces, to increase the size of a window. See also maximize. Compare minimize, reduce.

E notation n. See floating-point notation.

ENQ n. See enquiry character.

enquiry character n. Abbreviated ENQ. In communications, a control code transmitted from one station to request a response from the receiving station. In ASCII, the enquiry character is designated by decimal value 5 (hexadecimal 05).

en space n. A typographical unit of measure that is equal in width to half the point size of a particular font. Compare em space, fixed space, thin space.

Enter key n. The key that is used at the end of a line or command to instruct the computer to process the command or text. In word processing programs, the Enter key is used at the end of a paragraph. Also called: Return key.

Enterprise Application Integration n. See EAI.

enterprise computing n. In a large enterprise such as a corporation, the use of computers in a network or series of interconnected networks that generally encompass a variety of different platforms, operating systems, protocols, and network architectures. Also called: enterprise networking.

enterprise information portal n. A portal or gateway that allows internal and external users in a business or enterprise to access information from intranets, extranets, and the Internet for business needs. An enterprise information portal provides a simple Web interface that is designed to help users sift through large amounts of data quickly to find the information they need. By organizing all internal information from company servers, databases, e-mail, and legacy systems, the enterprise information portal exercises control over the company s information availability and presentation. Acronym: EIP. See also portal.

Enterprise JavaBeans n. An application programming interface (API) designed to extend the JavaBean component model to cross-platform, server-side applications that can run on the various systems usually present in an enterprise environment. Enterprise JavaBeans are defined in the Enterprise JavaBean specification released by Sun Microsystems, Inc. The goal of the API is to provide developers with a means of applying Java technology to the creation of reusable server components for business applications, such as transaction processing. Acronym: EJB. See also Java, JavaBean.

enterprise network n. In a large enterprise such as a corporation, the network (or interconnected networks) of computer systems owned by the enterprise, which fills the enterprise s various computing needs. This network can span diverse geographical locations and usually encompasses a range of platforms, operating systems, protocols, and network architectures.

enterprise networking n. See enterprise computing.

Enterprise Resource Planning n. An approach to business information management that relies on integrated application software to provide data on all aspects of the enterprise, such as manufacturing, finance, inventory, human resources, sales, and so on. The objective of Enterprise Resource Planning software is to provide data, when and as needed, to enable a business to monitor and control its overall operation. Acronym: ERP. Compare Material Requirements Planning.

entity n. In computer-aided design and object-oriented design, an item that can be treated as a unit and, often, as a member of a particular category or type. See also CAD, object-oriented design.

entry n. 1. A unit of information treated as a whole by a computer program. 2. The process of inputting information.

entry point n. A place in a program where execution can begin.

enumerated data type n. A data type consisting of a sequence of named values given in a particular order.

envelope n. 1. In communications, a single unit of information that is grouped with other items, such as error-checking bits. 2. The shape of a sound wave, caused by changes in amplitude. See the illustration.

Envelope.

envelope delay n. In communications, the difference in travel times of different frequencies in a signal. If the frequencies reach their destination at different times, signal distortion and errors can result. Also called: delay distortion.

environment n. 1. The configuration of resources available to the user. Environment refers to the hardware and the operating system running on it. For example, Windows and Macintosh are called windowing environments because they are based on screen regions called windows. 2. In microcomputing, environment refers to a definition of the specifications, such as command path, that a program operates in.

EOF n. See end-of-file.

EOL n. Acronym for end of line. A control (nonprinting) character that signals the end of a data line in a data file.

EOT n. See end-of-transmission.

EPIC n. 1. Short for Explicitly Parallel Instruction Computing. A technology developed jointly by Intel and Hewlett-Packard as the foundation of the 64-bit instruction set architecture incorporated in IA-64, the basis of the Merced chip. EPIC technology is designed to enable IA-64 processors to execute instructions efficiently and extremely quickly. Core elements include explicit parallelism based on software identification of instructions that the processor can execute concurrently; improved execution of branch paths; and earlier loads from memory. See also IA-64, Merced. 2. Short for Electronic Privacy Information Center. A public-interest research center based in Washington, D.C., dedicated to directing public attention toward civil liberties and online privacy related to electronic communication, cryptography, and related technologies.

epitaxial layer n. In semiconductors, a layer that has the same crystal orientation as the underlying layer.

EPP n. Acronym for Enhanced Parallel Port, a high-speed port for peripheral devices other than printers and scanners that is, for devices such as external drives. Specified in the IEEE 1284 standard, EPP describes bidirectional parallel ports that provide data throughput of 1 Mbps or more, as opposed to the 100 Kbps to 300 Kbps typical of the older, de facto standard Centronics ports. See also IEEE 1284, input/output port. Compare ECP.

EPP IEEE standard n. An IEEE standard relating to the Enhanced Parallel Port (EPP) protocol. This protocol was originally developed by Intel, Xircom, and Zenith Data Systems as a means to provide a high-performance parallel port link that would still be compatible with the standard parallel port. This protocol capability was implemented by Intel in the 386SL chip set (82360 I/O chip), prior to the establishment of the IEEE 1284 committee and the associated standards work. The EPP protocol offered many advantages to parallel port peripheral manufacturers and was quickly adopted by many as an optional data transfer method. A loose association of about 80 interested manufacturers was formed to develop and promote the EPP protocol. This association became the EPP Committee and was instrumental in helping to get this protocol adopted as one of the IEEE 1284 advanced modes. See also communications protocol, IEEE 1284, parallel port.

EPROM n. Acronym for erasable programmable read-only memory. A nonvolatile memory chip that is programmed after it is manufactured. EPROMs can be reprogrammed by removing the protective cover from the top of the chip and exposing the chip to ultraviolet light. Though EPROMs are more expensive than PROM chips, they can be more cost-effective if many changes are required. Also called: reprogrammable read-only memory (RPROM). See also EEPROM, PROM, ROM.

.eps n. The file extension that identifies Encapsulated PostScript files. See also EPS.

EPS n. Acronym for Encapsulated PostScript. A PostScript file format that can be used as an independent entity. The EPS image must be incorporated into the PostScript output of an application such as a desktop publisher. Many high-quality clip-art packages consist of such images. See also PostScript.

EPSF n. Acronym for Encapsulated PostScript file. See EPS.

equality n. The property of being identical, used most often in reference to values and data structures.

equalization n. A form of conditioning used to compensate for signal distortion and delay on a communication channel. Equalization attempts to maintain the amplitude and phase characteristics of a signal so that it remains true to the original when it reaches the receiving device.

equation n. A mathematical statement that indicates equality with the use of an equal sign (=) between two expressions. In programming languages, assignment statements are written in equation form. See also assignment statement.

erasable programmable read-only memory n. See EPROM.

erasable storage n. Storage media that can be used repeatedly because the user has the ability to erase whatever data was previously there. Most forms of magnetic storage, such as tape and disk, are erasable.

erase vb. To remove data permanently from a storage medium. This is usually done by replacing existing data with zeros or meaningless text or, in magnetic media, by disturbing the magnetic particles physical arrangement, either with the erase head or with a large magnet. Erase differs from delete in that delete merely tells the computer that data or a file is no longer needed; the data remains stored and is recoverable until the operating system reuses the space containing the deleted file. Erase, on the other hand, removes data permanently. See also erase head. Compare delete.

erase head n. The device in a magnetic tape machine that erases previously recorded information.

Eratosthenes sieve n. See sieve of Eratosthenes.

ergonomic keyboard n. A keyboard designed to reduce the risk of wrist and hand injuries that result from prolonged use or repetitive movement. An ergonomic keyboard can include such features as alternative key layouts, palm rests, and shaping designed to minimize strain. See also Dvorak keyboard, keyboard, Kinesis ergonomic keyboard.

ergonomics n. The study of people (their physical characteristics and the ways they function) in relation to their working environment (the furnishings and machines they use). The goal of ergonomics is to incorporate comfort, efficiency, and safety into the design of keyboards, computer desks, chairs, and other items in the workplace.

Erlang n. A concurrent functional programming language. Originally developed for controlling telephone exchanges, Erlang is a general-purpose language best suited for applications where rapid development of complex systems and robustness are essential. Erlang has built-in support for concurrency, distribution, and fault tolerance. The most widely implemented version of Erlang is the open source version.

ERP n. See Enterprise Resource Planning.

error n. A value or condition that is not consistent with the true, specified, or expected value or condition. In computers, an error results when an event does not occur as expected or when impossible or illegal maneuvers are attempted. In data communications, an error occurs when there is a discrepancy between the transmitted and received data. See also critical error, error message, error rate, error ratio, fatal error, hard error, inherent error, intermittent error, logic error, machine error, overflow error, parity error.. Compare fault.

error analysis n. The art and science of detecting errors in numeric calculations, especially in long and involved computations, where the possibility of errors increases.

error checking n. A method for detecting discrepancies between transmitted and received data during file transfer.

error control n. 1. The section of a program, procedure, or function that checks for errors such as type mismatches, overflows and underflows, dangling or illegal pointer references, and memory-use inconsistencies. 2. The process of anticipating program errors during software development.

error-correcting code n. See error-correction coding.

error-correction coding n. A method for encoding that allows for detection and correction of errors that occur during transmission. Data is encoded in such a way that transmission errors may be detected and corrected by examination of the encoded data on the receiving end. Most error-correction codes are characterized by the maximum number of errors they can detect and by the maximum number of errors they can correct. Error-correction coding is used by most modems. Also called: error-correcting code. See also error detection and correction. Compare error-detection coding.

error detection and correction n. A method for discovering and resolving errors during file transfer. Some programs only detect errors; others detect and attempt to fix them.

error-detection coding n. A method of encoding data so that errors that occur during storage or transmission can be detected. Most error-detection codes are characterized by the maximum number of errors they can detect. See also checksum. Compare error-correction coding.

error file n. A file that records the time and type of data processing and transmission errors.

error handling n. The process of dealing with errors (or exceptions) as they arise during the running of a program. Some programming languages, such as C++, Ada, and Eiffel, have features that aid in error handling. See also bug (definition 1).

error message n. A message from the system or program indicating that an error requiring resolution has occurred.

error rate n. In communications, the ratio of the number of bits or other elements that arrive incorrectly during transmission. For a 1200-bps modem, a typical error rate would be 1 in every 200,000 bits. See also parity, parity bit, Xmodem, Ymodem.

error ratio n. The ratio of errors to the number of units of data processed. See also error rate.

error trapping n. 1. The process by which a program checks for errors during execution. 2. The process of writing a function, program, or procedure such that it is capable of continuing execution despite an error condition.

escape character n. See ESC character.

escape code n. A character or sequence of characters that indicates that a following character in a data stream is not to be processed in the ordinary way. In the C programming language, the escape code is the backslash \.

Escape key n. A key on a computer keyboard that sends the escape (ESC) character to the computer. In many applications, the Escape key moves the user back one level in the menu structure or exits the program. See the illustration. See also Clear key.

Escape key.

escape sequence n. A sequence of characters that usually begins with the ESC character (ASCII 27, hexadecimal 1B), which is followed by one or more additional characters. An escape sequence escapes from the normal sequence of characters (such as text) and issues an instruction or command to a device or program.

ESC character n. One of the 32 control codes defined in the ASCII character set. It usually indicates the beginning of an escape sequence (a string of characters that give instructions to a device such as a printer). It is represented internally as character code 27 (hexadecimal 1B). Also called: escape character.

Esc key n. See Escape key.

ESD n. See electronic software distribution, electrostatic discharge.

ESDI n. Acronym for Enhanced Small Device Interface. A device that allows disks to communicate with computers at high speeds. ESDI drives typically transfer data at about 10 megabits per second, but they are capable of doubling that speed. Although fast, ESDI has been superseded by interfaces such as SCSI and EIDE. See also EIDE, SCSI.

ESP n. See enhanced serial port.

ESP IEEE standard n. Short for Encapsulating Security Payload IEEE standard. A standard for providing integrity and confidentiality to IP (Internet Protocol) datagrams. In some circumstances, it can also provide authentication to IP datagrams. See also authentication, datagram, IEEE, IP.

ESRB n. Acronym for Entertainment Software Rating Board. An independent, self-regulatory body providing ratings to the public and support to companies in the interactive software entertainment industry. The ESRB provides ratings for computer games and other interactive products such as Web sites, online games, and interactive chat.

e-tail n. See e-commerce.

e-text n. Short for electronic text. A book or other text-based work that is available on line in an electronic media format. An e-text can be read online or downloaded to a user s computer for offline reading. See also e-zine.

Ethernet n. 1. The IEEE 802.3 standard for contention networks. Ethernet uses a bus or star topology and relies on the form of access known as Carrier Sense Multiple Access with Collision Detection (CSMA/CD) to regulate communication line traffic. Network nodes are linked by coaxial cable, by fiberoptic cable, or by twisted-pair wiring. Data is transmitted in variable-length frames containing delivery and control information and up to 1500 bytes of data. The Ethernet standard provides for baseband transmission at 10 megabits (10 million bits) per second and is available in various forms, including those known as Thin Ethernet, Thick Ethernet, 10Base2, 10Base5, 10Base-F, and 10Base-T. The IEEE standard dubbed 802.3z, or Gigabit Ethernet, operates at 10 times 100 Mbps speed. See also ALOHAnet, baseband, bus network, coaxial cable, contention, CSMA/CD, Gigabit Ethernet, IEEE 802 standards, twisted-pair cable. 2. A widely used local area network system developed by Xerox in 1976, from which the IEEE 802.3 standard was developed.

Ethernet/802.3 n. The IEEE standard for 10- or 100-Mbps transmissions over an Ethernet network. Ethernet/802.3 defines both hardware and data packet construction specifications. See also Ethernet.

E-time n. See execution time.

etiquette n. See netiquette.

ETX n. See end-of-text.

Eudora n. An e-mail client program originally developed as freeware for Macintosh computers by Steve Dorner at the University of Illinois, now maintained in both freeware and commercial versions for both Macintosh and Windows by Qualcomm, Inc.

EULA n. See End-User License Agreement.

Euphoria n. Acronym for End User Programming with Hierarchical Objects for Robust Interpreted Applications. An interpreted programming language intended for general application development and game programming on MS-DOS, Windows, and Linux platforms.

European Computer Manufacturers Association n. See ECMA.

European Laboratory for Particle Physics n. See CERN.

EUV lithography n. Acronym for Extreme UltraViolet lithography. Manufacturing process allowing smaller circuits to be etched onto chips than is possible with traditional lithographic techniques. With this process, it is possible to economically produce chips that are much faster than those that are created using traditional processes. In EUV lithography, the image of a map of circuits to appear on a chip is bounced off a series of mirrors that condense the image. The condensed image is projected onto wafers containing layers of metal, silicon, and photosensitive material. Because EUV light has a short wavelength, extremely intricate circuit patterns can be created on the wafers.

evaluation n. The determination, by a program, of the value of an expression or the action that a program statement specifies. Evaluation can take place at compile time or at run time.

even parity n. See parity.

event n. An action or occurrence, often generated by the user, to which a program might respond for example, key presses, button clicks, or mouse movements. See also event-driven programming.

event-driven adj. Of, pertaining to, or being software that accomplishes its purpose by responding to externally caused events, such as the user pressing a key or clicking a button on a mouse. For example, an event-driven data entry form will allow the user to click on and edit any field at any time rather than forcing the user to step through a fixed sequence of prompts.

event-driven processing n. A program feature belonging to more advanced operating-system architectures such as the Apple Macintosh operating system, Windows, and UNIX. In times past, programs were required to interrogate, and effectively anticipate, every device that was expected to interact with the program, such as the keyboard, mouse, printer, disk drive, and serial port. Often, unless sophisticated programming techniques were used, one of two events happening at the same instant would be lost. Event processing solves this problem through the creation and maintenance of an event queue. Most common events that occur are appended to the event queue for the program to process in turn; however, certain types of events can preempt others if they have a higher priority. An event can be of several types, depending on the specific operating system considered: pressing a mouse button or keyboard key, inserting a disk, clicking on a window, or receiving information from a device driver (as for managing the transfer of data from the serial port or from a network connection). See also autopolling, event, interrupt.

event-driven programming n. A type of programming in which the program constantly evaluates and responds to sets of events, such as key presses or mouse movements. Event-driven programs are typical of Apple Macintosh computers, although most graphical interfaces, such as Windows or the X Window System, also use such an approach. See also event.

event handler n. 1. A method within a program that is called automatically whenever a particular event occurs. 2. A core function in JavaScript that handles client-side events. It is the mechanism that causes a script to react to an event. For example, common JavaScript event handlers coded in Web pages include onClick, onMouseOver, and onLoad. When the user initiates the action, such as a mouse over, the event handler executes, or carries out, the desired outcome. 3. In Java applets, rather than having a specific starting point, the applet has a main loop where it waits for an event or series of events (keystroke, mouse click, and so on). Upon occurrence of the event, the event handler carries out the instructions specified. See also applet, client, JavaScript.

event horizon n. The time at which hardware or software began to have the potential to encounter a Year 2000 problem. For instance, the event horizon in an accounting system in a company whose fiscal year ended on June 30, 1999, would be six months dating from January 1, 1999. Also called: time horizon to failure.

event log n. A file that contains information and error messages for all activities on the computer.

event logging n. The process of recording an audit entry in the audit trail whenever certain events occur, such as starting and stopping, or users logging on and off and accessing resources. See also event, service.

event procedure n. A procedure automatically executed in response to an event initiated by the user or program code, or triggered by the system.

event property n. A characteristic or parameter of an object that you can use to respond to an associated event. You can run a procedure or macro when an event occurs by setting the related event property.

e-wallet n. A program used in e-commerce that stores a customer s shipping and billing information to facilitate Web-based financial transactions. An e-wallet allows customers to instantly enter encrypted shipping and billing information when placing an order, rather than manually typing the information into a form on a Web page.

exa- prefix A prefix meaning 1 quintillion (10¹⁸ ). In computing, which is based on the binary (base-2) numbering system, exa- has a literal value of 1,152,921,504,606,846,976, which is the power of 2 (2⁶⁰ ) closest to one quintillion.Abbreviation: E.

exabyte n. Roughly one quintillion bytes, or a billion billion bytes, or 1,152,921,504,606,846,976 bytes. Abbreviation: EB.

Excel n. Microsoft s spreadsheet software for Windows PCs and Macintosh computers. Excel is part of the family of Office products. The most recent version, part of Office XP, includes the ability to access and analyze live data from the Web by simply copying and pasting Web pages into Excel. The first version of Excel was introduced for the Macintosh in 1985. Excel for Windows was released in 1987.

exception n. In programming, a problem or change in conditions that causes the microprocessor to stop what it is doing and handle the situation in a separate routine. An exception is similar to an interrupt; both refer the microprocessor to a separate set of instructions. See also interrupt.

exception handling n. See error handling.

exchangeable disk n. See removable disk.

exchange sort n. See bubble sort.

Excite n. A World Wide Web search engine developed by Excite, Inc. After conducting a search, Excite provides both a summary of each matching Web site it has located and a link to more information of the same type.

exclusive NOR n. A two-state digital electronic circuit in which the output is driven high only if the inputs are all high or all low.

exclusive OR n. A Boolean operation that yields true if and only if one of its operands is true and the other is false. See the table. Acronym: EOR. Also called: XOR. See also Boolean operator, truth table. Compare AND, OR.

Table E.1 Exclusive OR.

a	b	a XOR b
0	0	0
0	1	1
1	0	1
1	1	0

.exe n. In MS-DOS, a filename extension that indicates that a file is an executable program. To run an executable program, the user types the filename without the .exe extension at the prompt and presses Enter. See also executable program.

executable¹ adj. Of, pertaining to, or being a program file that can be run. Executable files have extensions such as .bat, .com, and .exe.

executable² n. A program file that can be run, such as file0.bat, file1.exe, or file2.com.

executable program n. A program that can be run. The term usually applies to a compiled program translated into machine code in a format that can be loaded into memory and run by a computer s processor. In interpreter languages, an executable program can be source code in the proper format. See also code (definition 1), compiler (definition 2), computer program, interpreter, source code.

execute vb. To perform an instruction. In programming, execution implies loading the machine code of the program into memory and then performing the instructions.

execute in place n. The process of executing code directly from ROM, rather than loading it from RAM first. Executing the code in place, instead of copying the code into RAM for execution, saves system resources. Applications in other file systems, such as on a PC Card storage device, cannot be executed in this way. Acronym: XIP.

execution time n. The time, measured in clock ticks (pulses of a computer s internal timer), required by a microprocessor to decode and carry out an instruction after it is fetched from memory. Also called: E-time. See also instruction time.

executive n. The set of kernel-mode components that form the base operating system for Microsoft Windows NT or later. See also operating system.

executive information system n. A set of tools designed to organize information into categories and reports. Because it emphasizes information, an executive information system differs from a decision support system (DSS), which is designed for analysis and decision making. Acronym: EIS. Compare decision support system.

exerciser n. A program that exercises a piece of hardware or software by running it through a large set of operations.

exit vb. In a program, to move from the called routine back to the calling routine. A routine can have more than one exit point, thus allowing termination based on various conditions.

expanded adj. A font style that sets characters farther apart than the normal spacing. Compare condensed.

expanded memory n. A type of memory, up to 8 MB, that can be added to IBM PCs. Its use is defined by the Expanded Memory Specification (EMS). Expanded memory is not accessible to programs in MS-DOS, so the Expanded Memory Manager (EMM) maps pages (blocks) of bytes from expanded memory into page frames in accessible memory areas. Expanded memory is not needed in Windows 9x, all versions of Windows NT, and Windows 2000. See also EEMS, EMS, Expanded Memory Manager, page frame.

Expanded Memory Manager n. A driver that implements the software portion of the Expanded Memory Specification (EMS) to make expanded memory in IBM and compatible PCs accessible. Acronym: EMM. See also EMS, expanded memory, extended memory.

Expanded Memory Specification n. See EMS.

expansion n. A way of increasing a computer s capabilities by adding hardware that performs tasks that are not part of the basic system. Expansion is usually achieved by plugging printed circuit boards (expansion boards) into openings (expansion slots) inside the computer. See also expansion board, expansion slot, open architecture (definition 2), PC Card, PCMCIA slot.

expansion board n. A circuit board that is plugged into a computer s bus (main data transfer path) to add extra functions or resources to the computer. Typical expansion boards add memory, disk drive controllers, video support, parallel and serial ports, and internal modems. For laptops and other portable computers, expansion boards come in credit card-sized devices called PC Cards that plug into a slot in the side or back of the computer. Also called: expansion board, extender board. See also expansion slot, PC Card, PCMCIA slot.

expansion bus n. A group of control lines that provide a buffered interface to devices. These devices can be located either on the system board or on cards that are plugged into expansion connectors. Common expansion buses included on the system board are USB, PC Card, and PCI. See also AT bus.

expansion card n. See expansion board.

expansion slot n. A socket in a computer, designed to hold expansion boards and connect them to the system bus (data pathway). Expansion slots are a means of adding or enhancing the computer s features and capabilities. In laptop and other portable computers, expansion slots come in the form of PCMCIA slots designed to accept PC Cards. See also expansion board, PC Card, PCMCIA slot.

experience points n. Often used in role-playing games (RPGs), experience points are a way of measuring how much a player has experienced or learned. As a player moves through a game, additional benefits, often in the form of increased statistics or skills, are earned. These points are frequently spent or used by the player to increase his or her score. See also computer game, role-playing game.

expert system n. An application program that makes decisions or solves problems in a particular field, such as finance or medicine, by using knowledge and analytical rules defined by experts in the field. It uses two components, a knowledge base and an inference engine, to form conclusions. Additional tools include user interfaces and explanation facilities, which enable the system to justify or explain its conclusions as well as allowing developers to run checks on the operating system. See also artificial intelligence, inference engine, intelligent database, knowledge base.

expiration date n. The date on which a shareware, beta, or trial version of a program stops functioning, pending purchase of the full version or the entry of an access code.

expire vb. To stop functioning in whole or in part. Beta versions of software are often programmed to expire when a new version is released. See also beta².

Explicitly Parallel Instruction Computing n. See EPIC.

exploded view n. A form of display that shows a structure with its parts separated but depicted in relation to each other. See the illustration.

Exploded view.

Explorer n. See Internet Explorer, Windows Explorer.

ExploreZip n. A destructive virus that attacks computers running Windows, where it first appears as an e-mail attachment named zipped_files.exe. ExploreZip affects local drives, mapped drives, and accessible network machines and destroys both document and source-code files by opening and immediately closing them, leaving a zero-byte file. Described as both a Trojan horse (because it requires the victim to open the attachment) and a worm (because it can propagate itself in certain instances), ExploreZip spreads by mailing itself to the return address of every unread e-mail in the inbox of the computer s e-mail program, as well as by searching for and copying itself to the Windows directory on mapped drives and networked machines. See also Trojan horse, virus, worm.

exponent n. In mathematics, a number that shows how many times a number is used as a factor in a calculation; in other words, an exponent shows that number s power. Positive exponents, as in 2³, indicate multiplication (2 times 2 times 2). Negative exponents, as in 2^-3, indicate division (1 divided by 2³ ). Fractional exponents, as in 8^1/3, indicate the root of a number (the cube root of 8).

exponential notation n. See floating-point notation.

exponentiation n. The operation in which a number is raised to a given power, as in 2³. In computer programs and programming languages, exponentiation is often shown by a caret (^), as in 2^3.

export vb. To move information from one system or program to another. Files that consist only of text can be exported in ASCII (plain text format). For files with graphics, however, the receiving system or program must offer some support for the exported file s format. See also EPS, PICT, TIFF. Compare import.

export n. In NFS, a file or folder made available to other network computers using the NFS mount protocol. See also NFS.

expression n. A combination of symbols identifiers, values, and operators that yields a result upon evaluation. The resulting value can then be assigned to a variable, passed as an argument, tested in a control statement, or used in another expression.

extended ASCII n. Any set of characters assigned to ASCII values between decimal 128 and 255 (hexadecimal 80 through FF). The specific characters assigned to the extended ASCII codes vary between computers and between programs, fonts, or graphics characters. Extended ASCII adds capability by allowing for 128 additional characters, such as accented letters, graphics characters, and special symbols. See also ASCII.

Extended Binary Coded Decimal Interchange Code n. See EBCDIC.

extended characters n. Any of the 128 additional characters in the extended ASCII (8-bit) character set. These characters include those used in several foreign languages, such as accent marks, and special symbols used for creating pictures. See also extended ASCII.

extended data out random access memory n. See EDO RAM.

Extended Edition n. A version of OS/2 with built-in database and communications facilities, developed by IBM. See also OS/2.

eXtended Graphics Array n. An advanced standard for graphics controller and display mode design, introduced by IBM in 1990. This standard supports 640 x 480 resolution with 65,536 colors, or 1024 x 768 resolution with 256 colors, and is used mainly on workstation-level systems. Acronym: XGA.

Extended Industry Standard Architecture n. See EISA.

extended memory n. System memory beyond 1 megabyte in computers based on the Intel 80x86 processors. This memory is accessible only when an 80386 or higher-level processor is operating in protected mode or in emulation on the 80286. To use extended memory, MS-DOS programs need the aid of software that temporarily places the processor into protected mode or by the use of features in the 80386 or higher-level processors to remap portions of extended memory into conventional memory. Extended memory is not an issue in Windows 9x, all versions of Windows NT, Windows 2000, and Windows XP. See also EMS, extended memory specification, protected mode.

extended memory specification n. A specification developed by Lotus, Intel, Microsoft, and AST Research that defines a software interface allowing real-mode applications to use extended memory and areas of memory not managed by MS-DOS. Memory is managed by an installable device driver, the Expanded Memory Manager (EMM). The application must use the driver to access the additional memory. Acronym: XMS. See also Expanded Memory Manager, extended memory.

extended VGA n. An enhanced set of Video Graphics Array (VGA) standards that is capable of displaying an image of from 800 x 600 pixels to 1600 x 1200 pixels and that can support a palette of up to 16.7 million (2²⁴ ) colors. This palette approaches the 19 million colors that a normal person can distinguish, so it is considered a digital standard for color realism that parallels analog television. Also called: Super VGA, SVGA. See also analog-to-digital converter, CRT, VGA.

extender board n. See expansion board.

eXtensible Firmware Interface n. In computers with the Intel Itanium processor, the interface between the operating system and the computer s low-level booting and initialization firmware. The interface is made up of data tables that contain platform-related information, plus boot and run-time service calls that are available to the operating system and its loader to provide a standard environment for booting an operating system and running preboot applications. Acronym: EFI.

Extensible Forms Description Language or eXtensible Forms Description Language n. See XFDL.

Extensible Hypertext Markup Language n. See XHTML.

extensible language n. A computer language that allows the user to extend or modify the syntax and semantics of the language. In the strict sense, the term relates to only a few of the languages actually used that allow the programmer to change the language itself, such as Forth. See also computer language, semantics (definition 1), syntax.

Extensible Markup Language or eXtensible Markup Language n. See XML.

extensible style language n. See XSL.

eXtensible Stylesheet Language n. See XSL.

eXtensible Stylesheet Language Formatting Objects n. See XSL-FO.

Extensible Stylesheets Language-Transformations n. See XSLT.

extension n. 1. A set of characters added to a filename that serves to extend or clarify its meaning or to identify a file as a member of a category. An extension may be assigned by the user or by a program, as, for example, .com or .exe for executable programs that MS-DOS can load and run. 2. A supplemental set of codes used to include additional characters in a particular character set. 3. A program or program module that adds functionality to or extends the effectiveness of a program. 4. On the Macintosh, a program that alters or augments the functionality of the operating system. There are two types: system extensions, such as QuickTime, and Chooser extensions, such as printer drivers. When a Macintosh is turned on, the extensions in the Extensions folder within the System folder are loaded into memory. See also Chooser extension, QuickTime, System folder.

Extension Manager n. A Macintosh utility developed by Apple that allows the user to determine which extensions are loaded when the computer is turned on. See also extension (definition 4).

extent n. On a disk or other direct-access storage device, a continuous block of storage space reserved by the operating system for a particular file or program.

exterior gateway protocol n. A protocol used by routers (gateways) on separate, independent networks for distributing routing information between and among themselves for example, between hosts on the Internet. Acronym: EGP. Also called: external gateway protocol. Compare interior gateway protocol.

external command n. A program included in an operating system such as MS-DOS that is loaded into memory and executed only when its name is entered at the system prompt. Although an external command is a program in its own right, it is called a command because it is included with the operating system. See also XCMD. Compare internal command.

external function n. See XFCN.

External Gateway Protocol n. A protocol for distributing information regarding availability to the routers and gateways that interconnect networks. Acronym: EGP. See also gateway, router.

external gateway protocol n. See exterior gateway protocol.

external hard disk n. A free-standing hard disk with its own case and power supply, connected to the computer with a data cable and used mainly as a portable unit. See also hard disk.

external interrupt n. A hardware interrupt generated by hardware elements external to the microprocessor. See also hardware interrupt, internal interrupt, interrupt.

external modem n. A stand-alone modem that is connected via cable to a computer s serial port. See also internal modem.

external reference n. A reference in a program or routine to some identifier, such as code or data, that is not declared within that program or routine. The term usually refers to an identifier declared in code that is separately compiled. See also compile.

external storage n. A storage medium for data, such as a disk or tape unit, that is external to a computer s memory.

external viewer n. A separate application used to view documents that are of a type that cannot be handled by the current application. See also helper program.

extract vb. 1. To remove or duplicate items from a larger group in a systematic manner. 2. In programming, to derive one set of characters from another by using a mask (pattern) that determines which characters to remove.

extra-high-density floppy disk n. A 3.5-inch floppy disk capable of holding 4 MB of data and requiring a special disk drive that has two heads rather than one. See also floppy disk.

extranet n. An extension of a corporate intranet using World Wide Web technology to facilitate communication with the corporation s suppliers and customers. An extranet allows customers and suppliers to gain limited access to a company s intranet in order to enhance the speed and efficiency of their business relationship. See also intranet.

extrinsic semiconductor n. A semiconductor that conducts electricity due to a P-type or N-type impurity that allows electrons to flow under certain conditions, such as heat application, by forcing them to move out of their standard state to create a new band of electrons or electron gaps. See also N-type semiconductor, P-type semiconductor, semiconductor.

eyeballs n. The individuals or the number of individuals who view a Web site or its advertising.

e-zine or ezine n. Short for electronic magazine. A digital publication available on the Internet, a bulletin board system (BBS), or other online service, often free of charge.