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Barrons Publishing Dictionary of Computer and Internet Terms 10th

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/etc in UNIX, a directory that contains system configuration information; often pronounced “et-see.”

Ethernet a type of local-area network originally developed by Xerox Corporation. Communication takes place by means of radio-frequency signals carried by a coaxial cable. The name “Ethernet” apparently comes from “aether,” the 19th-century name for the medium through which light waves were thought to travel. See LOCAL-AREA NETWORK;


On the physical level, there are four types of Ethernet connections. Thinwire Ethernet uses RG-58 coaxial cable. Twisted-pair Ethernet is similar but uses a pair of unshielded wires. Conventional baseband Ethernet uses a thicker coaxial cable about 38 inch (0.9 cm) in diameter, and broadband Ethernet modulates the whole Ethernet signal on a higher-frequency carrier so that several signals can be carried simultaneously on a single cable, just like cable TV channels. See 10BASE-2; 10BASE-T; 100BASE-T.

The control strategy of Ethernet is called CSMA/CD (Carrier Sense, Multiple Access, Collision Detection). Each computer listens to see if another computer is transmitting. If so, it waits its turn to transmit. If two computers inadvertently transmit at the same time, the collision is detected, and they retransmit one at a time.

Ethernet systems use many software protocols, including TCP/IP, IPX/SPX, and NetBEUI. See MAC ADDRESS; NETBEUI; PROTOCOL; TCP/IP.

ethical hacking the practice of breaking into computers without malicious intent, simply to find security hazards and report them to the people responsible.

The concept of “ethical hacking” is questionable because most people do not want strangers trying to break into their computers, no matter how benign the motives. Malicious CRACKERs almost always claim to be “ethical hackers” when caught. We do not allow strangers to attempt “ethical burglary.” Experiments to test the security of a system should only be done with the advance permission of the victim.

Eudora a pioneering e-mail program, widely available for PC and Macintosh computers, distributed free of charge from www.eudora.com. It was developed by Steve Dorner starting in 1988. He named it after the writer Eudora Welty (1909–2001), who wrote a short story, “Why I Live at the P.O.,” about the importance of mail.

EULA abbreviation for end-user license agreement, the agreement that the user of a piece of software is required to accept when installing it. See


Euro the common European currency introduced in 1999 to replace national currencies in Austria, Belgium, Finland, France, Germany, Ireland, Italy, Luxembourg, the Netherlands, Portugal, and Spain. More information about the European currency is available from the European Union at www.europa.eu.int and the European Central Bank, which manages the currency, at www.ecb.int.



The Euro symbol is shown in Figure 96. In Windows, this can be typed by holding down Alt and typing 0128 on the numeric keypad. However, to display and print this symbol, users of versions prior to Windows 2000 may need to download updated fonts from www.microsoft.com.

FIGURE 96. Euro currency symbol

European paper sizes see PAPER SIZES (ISO).


1. (exposure value) in photography, a number that measures the effect of f-ratio and shutter speed together, as exposure adjustments. For example, an exposure of 1/250 second at f /8 is equivalent to 1/125 second at f /11; each of these is EV 14. Higher EV numbers correspond to shorter exposures or exposures at smaller apertures (higher-numbered f-stops). Adding 1 to the EV is equivalent to cutting the exposure in half. Thus, 1/250 second at f /11 is EV 15.

Cameras often have “EV +/–” adjustments to deliberately increase or decrease the exposure. Here +1 means to expose more than the meter indicates, and 1 means to expose less than the meter indicates.

See also F-RATIO.

2. (Extended Validation) a type of digital certificate with additional verification requirements to ensure that the certificate holder is really who they claim to be. (Web address: www.cabforum.org). See CERTIFICATE, DIGITAL.

EVDO (Evolution Data Optimized) a system for wireless broadband (web address: www.evdoinfo.com). Contrast HSDPA.

even smalls type that is set in all small capital letters, with no lower case letters, LIKE THIS. The cross-references in this book are set in even smalls.

Contrast C/SC.

event-driven programming programming in which the computer spends its time responding to events rather than stepping through a prearranged series of actions. Computers that control machinery are almost always event-driven. So are computer programs that run under graphical user interfaces such as the Macintosh operating system or Microsoft Windows. Such programs respond to events such as the user choosing an item on a menu or clicking the mouse on an icon. See GRAPHICAL USER INTERFACE; OBJECT-ORIENTED PROGRAMMING; VISUAL BASIC; WINDOW.

evil twin a malicious wireless hot spot that seems legitimate, but is designed to trick unwitting users into revealing personal information.

EX (describing items for sale) “excellent,” i.e., fully functional and undamaged. Particularly in the used-camera trade, EX applies to reliable, working equipment that shows some visible wear.

EX+ (describing items for sale) better than EX (i.e., fully functional and only slightly worn). Compare LN, LN–.



exa- metric prefix meaning ×1,000,000,000,000,000,000 (1018). Exa- is derived from the Greek word for “beyond” or “outside.” See METRIC PREFIXES.

Excel a popular SPREADSHEET program, originally released in 1985 by Microsoft for the Macintosh, and later adapted for Microsoft Windows.

exception a situation that prevents a computer program from running as specified, such as unexpectedly reaching the end of a file or trying to divide by zero. See also TRY; UNHANDLED EXCEPTION.

Exchange Server popular Microsoft software for electronic mail and other collaboration. Users run client software such as Outlook on their machines, which connect to the Exchange software on a server. See www.microsoft.com/exchange/evaluation/whatis.mspx.

exclusive-OR gate see XOR GATE.

exe file a file with EXTENSION .exe, containing an executable machine-lan- guage program for Windows. To execute it, simply double-click on it; right-click on it and choose Run; or type its name at a command prompt.

Most application programs are distributed as .EXE files. Most compilers translate source code into .EXE files. See COMPILER. Contrast BAT FILE; COM (definition 2).

Caution! Do not run .exe files received via e-mail because they are almost certainly viruses.

execute to do what an instruction says to do. A computer alternates between a fetch cycle, when it locates the next instruction, and an execute cycle, when it carries the instruction out. See COMPUTER ARCHITECTURE.

executive size a size of paper sometimes used for stationery in the United States, 714 × 1012 inches (18.4 cm × 26.7 cm).

EXIF (exchangeable image file format) a standard way of including METADATA in JPEG and some other file formats, mainly to preserve information about the digital camera and the camera settings used to create an image. The EXIF standard is maintained by the Japan Electronics and Information Technology Association (JEITA, www.jeita.or.jp). Unofficial but useful information about EXIF is maintained at www.exif.org.

exit to clear an application program from memory; to QUIT. Most software prompts you to save changes to disk before exiting. Read all message boxes carefully. Compare CLOSE.

exp the function, in many programming languages, that calculates the value of ex. See E.

Expansion in computer games, a supplement to the original game that adds features and content. It is important to note that expansions usually do not include the original game software, which must be purchased separately.

expert set a FONT that includes a full set of accented vowels, ligatures, small caps, and other special characters (such as an extended group of CASE




FRACTIONs). It is assumed that someone using such a font will have the knowhow and the software to be able to set the special characters. Not every typeface has a matching expert set; you may have to take this into consideration when selecting a typeface for a particular job or when purchasing fonts.

FIGURE 97. Expert set (Minion typeface, partial font)

expert system a computer program that uses stored information to draw conclusions about a particular case. It differs from a database, which merely calls up stored information and presents it to the user unchanged. Expert systems are widely used to troubleshoot defects in machines; they have also been used successfully to diagnose diseases or recommend manufactured products.

Every expert system consists of three parts: (1) a user interface, which is a way of communicating with the user through such devices as menus, commands, or short-answer questions (see USER INTERFACE); (2) a knowledge base containing stored expertise; and (3) an inference engine, which draws conclusions by performing simple logical operations on the knowledge base and the information supplied by the user. See also



1.(noun) a way of breaching the security of a system or using features that should be inaccessible. Often written and pronounced sploit.

2.A piece of software designed to make it easy for a large number of would-be hackers to take advantage of such a software flaw.

Explorer the part of Windows that is used for exploring directories, files, and desktop menus. To access it, right-click on the and choose “Explore.” (See Figure 98 on page 180.)

exponent a number or letter that indicates repeated multiplication. Thus the exponent n in the expression an means to multiply n number of a’s together. For example:

32 = 3 × 3 = 9 45 = 4 × 4 × 4 × 4 × 4 = 1,024

106 = 10 × 10 × 10 × 10 × 10 × 10 = 1,000,000

Also, a2 = a × a is called a to the second power, or a squared. The number that when multiplied by itself gives a is called the square root of a

(written as a ). That means a × a = a. For example, 9 = 3, since 3 × 3 = 9.

exponential function


FIGURE 98. Explorer (Windows)

exponential function a function of the form y = ax, where a can be any positive number except 1 and is called the base of the function. The most commonly used exponential function is ex. See E.

exponential notation (scientific notation, E format) a way of writing very large or very small numbers conveniently. For example, 2,500,000 can be written as 2.5 × 106 or (in E format) 2.5E6 or 2.5E+6. For very small numbers, the exponent is negative; thus 0.003 = 3.0 × 103 = 3.0E-3.

export to save a file in a format other than the application program’s native format. Many word processing and graphics programs have the ability to export to several different formats. Look under the “Save As. . . ” dialog box for the available file formats.

Because the export process is a type of file conversion (instead of a simple copy operation) there is the possibility of a loss of image quality or text formatting.

ExpressCard a type of add-on card for laptop computers introduced by the Personal Computer Memory Card International Association (PCMCIA) in 2003 to replace the earlier CardBus (PC Card, PCMCIA Card) standard. ExpressCards are much faster, since they combine USB 2.0 and PCI Express communication.

Note: An ExpressCard slot and a CardBus (PC Card) slot look alike from outside the computer, but if you insert the wrong kind of card, no connection is made (and no damage occurs). A CardBus card is 2.1 inches (54 mm) wide. An ExpressCard can be the same width, but it narrows to 1.6 inches (34 mm) at the connector end, and many ExpressCards are that width along their entire length.

expression a series of symbols that can be evaluated to have a particular value. For example, 2 + 3 is an expression that evaluates to 5.

Extended Industry Standard Architecture see EISA.


external viewer

extends in C++ and Java, a keyword indicating that a class inherits all of the functionality of another class, and then adds additional data or methods. Instead of extends, C# uses a colon (:). For example, all program- mer-defined Java applet classes include a declaration similar to this:

class myapplet extends Applet

This allows the class you write (myapplet) to include all of the features defined in the standard class Applet.


1.anything that adds capabilities to an existing system. For example, optional components of the Macintosh operating system are called extensions.

2.the part of a filename following the period, in Windows and other operating systems. For example, the filename myfile.txt has .txt as its extension.

The purpose of extensions is to indicate the type of file, but it is important to realize that the extension does not actually cause the file to be of a particular type; you can rename any file to have any extension, but when you do, your software may no longer recognize it for what it is.

Some file extensions have standard meanings; see Table 6 on page 182. See the individual entries in this book for more information on some of the more important types.

A practical problem arises when the same extension is used by different software packages for different purposes. For example, .tex denotes

both a TEX word processing document and a Corel Draw texture. When this happens, an extension may end up associated with the wrong piece of software. See ASSOCIATE for information on how to change the software that is associated with a particular extension.

Prior to Windows 95, all extensions could be no more than three characters. Newer file extensions can be longer.

FIGURE 99. Extensions, hidden (top) and visible (bottom).

In Windows, it is up to the user whether extensions are displayed or hidden (Fig. 99). The choice is under Tools, Folder Options, in any window displaying files or folders.

Note that you can be tricked by a filename with two extensions. If someone sends you a file named virus.txt.exe and extensions are hidden, you will see the name as virus.txt and think it is a text file, but if you open it, it will actually execute as a program.

external viewer see VIEWER.

external viewer






Adobe Illustrator subset of .eps



ASCII text file

.bak, .bk


Backup copy of a file that has been edited



BASIC program file



Batch job (file of commands, DOS or Windows)



Bitmap graphics file



C program file



Vector graphics (CorelDraw)



Java bytecode file



Command file (smaller version of .exe)



C++ program file



C# program file

.doc, docx


Document file (ASCII or Microsoft Word)



Dynamic link library



Encapsulated PostScript graphics



Executable file (machine-language program)



Bitmap graphics file (GIF format)



Help file

.htm, .html


Hypertext Markup Language



Icon (Windows)



Initialization file (configuration settings)



Java program source file

.jpeg, .jpg


Compressed graphics (popular on the Web)



Log of installation or usage (various software)



Makefile (Visual Basic and other environments)



Windows shortcut

.mid, .midi


MIDI digitized music file



MP3 digitized audio file



Pascal program file



Portable Document Format (images of printed pages)



Project file (various compilers)



Perl or Prolog program

.ppt, .pptx


PowerPoint presentation



PostScript printable file



Outlook e-mail archive file



Image file



Rich Text Format word processing file



Screen saver (in .exe format)



Shockwave file



TeX document

.tif, .tiff


Bitmap graphics file (TIFF format)



TrueType font



Temporary file



ASCII text file



Sound wave file

.wks, .wk2,


Lotus 1-2-3 or Microsoft Works worksheet



Windows Media audio (music)

.wp, .wpd,


WordPerfect document

.xls, .xlsx


Excel worksheet file



ZIP compressed file






extranet a network using Internet protocols that allows a company to share information with other companies (such as suppliers and customers) but with security features preventing access to others. See VPN; PROTOCOL.

Contrast INTRANET.

Extreme Programming (or eXtreme Programming, abbreviated XP) a programming methodology introduced by Kent Beck and others in 1999.

The key idea is never to write a long computer program without knowing whether it will work. Instead, build every program out of small pieces that can be tested individually. This often requires writing substitutes (STUBs) for unfinished routines so that the rest of the program can be tested.

Extreme Programming also includes other good management practices, such as encouraging teamwork and keeping working hours reasonable. Nothing in Extreme Programming is radically new or “extreme;” much of it reflects the way the best programmers have always worked. See SOFTWARE ENGINEERING.

Despite the abbreviation XP, Extreme Programming has no specific connection to Microsoft Windows XP, as far as we can determine.

extrude a special effect provided by drawing programs that creates a threedimensional shadow. It looks as if the type (actually any object) has been squeezed out from a cookie gun.

FIGURE 100. Extruded type

eyedropper a tool available in paint programs that allows you to match a color in the existing picture, and cause it to become the active color (Figure 101). All you have to do is click the eyedropper on the area of color you desire and that becomes the selected color. You can sample for your primary, secondary, and background colors.

FIGURE 101. Eyedropper tool

If at first this tool seems senseless, consider what would happen if you were working on a digitized 24-bit color photograph. There are literally millions of colors available in this format—how are you going to find the right one to extend that background shade over that telephone line? Or how are you going to remember which of those colors you were using yesterday? The eyedropper will let you pick up the right color to use. See


eyeglasses, computer


eyeglasses, computer eyeglasses for viewing a computer screen two or three feet away. Most eyeglasses are designed for vision at a great distance or for reading at about 18 inches (46 cm). Neither of these is suitable for looking at a computer screen. Moreover, the screen cannot be seen properly through the dividing line or transition region of bifocals. In addition, the slight fuzziness of screen images causes some people’s eyes to strain as they try to focus. As a result, many eyeglass wearers think the computer has harmed their vision, although in fact there is no evidence that computer work (or any other kind of close work) harms the eyes.

Computer screens emit tiny amounts of ultraviolet (UV) light, and special glasses are available that block this. However, there is much more UV in ordinary sunlight than in the image on a computer screen, so UV-blocking glasses are probably more beneficial outdoors than in the office.



fair use


F keys see

f-ratio the focal length of a lens divided by the clear aperture (diameter) through which light enters. The adjustment for f-ratio is called the


The f-ratio determines the brightness of the image formed by the lens; lower f-ratios produce brighter images. Thus, a camera with an f/1.8 lens requires much less light to take a picture than a camera with an f/ 8 lens, even with the same film or electronic image sensor.

The brightness of the image is inversely proportional to the square of the f-ratio. That is why f-stops on lenses are often numbered as powers of 2 : f/2, 2.8, 4, 5.6, 8, and so on. Each f-stop gives half as bright an image as the next larger (lower-numbered) one.

To increase or decrease exposure n “stops” means to increase it or decrease it by 2n. Thus a one-stop decrease means to cut the exposure in half, and a two-stop decrease means to cut it to 14 of its original value.

The rated f-ratio of a lens refers to its widest opening; smaller openings (higher f-ratios) are provided as an automatic or manual adjustment. The actual front glass element is much larger than the opening that the light must pass through. The f-ratio of a ZOOM lens generally varies as the focal length is changed.


f-stop the adjustment for selecting the F-RATIO of a lens. Choose a smaller aperture (higher-numbered f-stop) for greater DEPTH OF FIELD.

fabric network interconnections.

Facebook a social networking site (www.facebook.com). Because Facebook was originally restricted to school campuses, it is the most popular service with students.

facsimile see FAX.

factorial the product of all the integers from 1 up to a specified number. The factorial of a number n is symbolized by an exclamation point: n!. For example:

2! = 2

× 1



= 2

3! = 3

× 2

× 1


= 6

4! = 4 × 3 × 2 × 1


= 24

5! = 5

× 4

× 3 × 2

× 1

= 120


fair use in copyright law, a limited kind of use of copyrighted material that does not require the copyright holder’s permission. For example, quoting a few sentences from a book and acknowledging the source is fair use.

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