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Dictionary of
Computer and
Internet Terms

Tenth Edition

Douglas A. Downing, Ph.D.

School of Business and Economics

Seattle Pacific University

Michael A. Covington, Ph.D.

Artificial Intelligence Center

The University of Georgia

Melody Mauldin Covington

Covington Innovations

Athens, Georgia

Catherine Anne Covington

Covington Innovations

Athens, Georgia

With the assistance of
Sharon Covington


Douglas Downing teaches economics and quantitative methods at the School of Business and Economics at Seattle Pacific University. He is the author of several books in both Barron’s Easy Way and Business Review series. He is also the author of Java Programming the Easy Way and Dictionary of Mathematics Terms, published by Barron’s Educational Series, Inc. He holds the Ph.D. degree in economics from Yale University.

Michael Covington is Associate Director of the Artificial Intelligence Institute at the University of Georgia. He is the author of several books and over 250 magazine articles. He holds the Ph.D. degree in linguistics from Yale University.

Melody Mauldin Covington is a graphic designer living in Athens, Georgia. She is the author of Dictionary of Desktop Publishing (published by Barron’s).

Catherine Anne Covington is a student at the Lamar Dodd School of Art (University of Georgia).

Sharon Covington is a student at Emory University.

© Copyright 2009, 2006, 2003, 2000, 1998, 1996, 1995, 1992, 1989, and 1986 by Barron’s Educational Series, Inc.

All rights reserved.

No part of this book may be reproduced or distributed in any form or by any means without the written permission of the copyright owner.

All inquiries should be addressed to:

Barron’s Educational Series, Inc. 250 Wireless Boulevard Hauppauge, NY 11788 www.barronseduc.com

ISBN-13: 978-0-7641-4105-8

ISBN-10: 0-7641-4105-8

Library of Congress Catalog Card No. 2008044365

Library of Congress Cataloging-in-Publication Data

Downing, Douglas.

Dictionary of computer and Internet terms / Douglas A. Downing, Michael A. Covington, Melody Mauldin Covington. — 10th ed.
p. cm.

ISBN 978-0-7641-4105-8

1. Computers—Dictionaries. 2. Internet—Dictionaries. I. Covington, Michael A., 1957– II. Covington, Melody Mauldin. III. Title.

QA76.15.D667 2009
004.03—dc22 2008044365


9 8 7 6 5 4 3 2 1


About the Authors ii

To the Reader iv

Dictionary of Computer and Internet Terms 1

Numbers 1

Greek Letters 5

A 7

B 38

C 71

D 124

E 159

F 185

G 211

H 223

I 242

J 264

K 272

L 276

M 296

N 322

O 336

P 349

Q 389

R 392

S 421

T 468

U 498

V 510

W 521

X 538

Y 543

Z 545

Visual Dictionary of Characters and Symbols 547

Country Codes for Top-Level Domains 552


Computers are no longer just for specialists. Today, computing is not just a profession and a hobby; it is also a tool used in virtually all human activities.

That’s why we’ve compiled this book of background knowledge. Its pur-pose is to tell you the things other people think you already know.

We design this book to have a convenient size so it can be easily carried around. In compiling a book this size, we have had to be selective. The quickest way to identify a word that you can’t find in a book is probably to do a web search (see SEARCH ENGINE). Also, some terms are almost always abbreviated, and in that case you should look for the abbreviation rather than the full term.

Much has changed since the first edition of this book was published more than twenty years ago. New terms are being invented every day. We regularly update the book, and this edition contains new entries on a vari-ety of topics including Windows Vista and Mac OS X. We’ve also cut out material that was showing its age.

Terms are marked slang or humorous if they are seldom used in serious writing. They are marked as jargon if, in our estimation, they are somewhat pretentious new names for old concepts and are not likely to endure. We provide occasional Usage notes to explain grammar, spelling, and proper use of words, such as the exact difference between disc and disk.

Throughout, we use SMALL CAPITALS to mark important words that are defined elsewhere in this book. By following cross-references, you can quickly find many entries that pertain to whatever interests you. Here are some entries you may wish to start with to learn about particular topics:

• Internet culture: CHAT ROOM
• right and wrong: COMPUTER ETHICS
• safe computing: COMPUTER SECURITY
• solving exceptionally difficult problems: ARTIFICIAL INTELLIGENCE
• productively using computers in business and daily life: APPLICATION


• listening to music: DIGITAL MUSIC
• taking pictures: DIGITAL CAMERA
• creating web pages: HTML
• writing computer programs: PROGRAMMING LANGUAGE
• software that controls a computer: OPERATING SYSTEM
• how a computer works: COMPUTER ARCHITECTURE
• networking and the Internet: INTERNET
• connecting computers wirelessly: WIRELESS COMMUNICATION
• electronic components: TRANSISTOR



Be sure to notice the visual dictionary of symbols at the end of the book. If you don’t know what ∑ or ≈ or • is called, don’t worry; you can look it up there.

All four of us want to thank The University of Georgia and Seattle Pacific University for access to facilities and for accommodating us as we worked on the project. We also want to thank Robert Downing for help with 1960s data processing terminology; Sharon Covington for help with current Internet culture; and Brantley Coile of Coraid, Inc., for permission to adapt material from Coraid’s glossary of networking and data storage.

Many of the words used in this book are registered trademarks. We have made no attempt to determine or report their legal status. For further infor-mation about any product name, consult the manufacturer’s literature.

1 10base-2


1-2-3 see LOTUS 1-2-3.

3Com a leading producer of networking hardware, mainly focusing on res-idential and small to medium businesses. In recent years the company has sharpened its focus in this area by acquiring U.S. Robotics but sell-ing off Palm (see PALM). Their web address is www.3com.com.


4, 8, 16 . . . 64 (etc.) describing a CD or DVD drive, able to transfer data at 4, 8, 16 (etc.) times the speed of normal audio or video. For example, a 16 CD-R drive can record a full CD, equivalent to about an hour of audio, in about four minutes.

5.1 a format of SURROUND SOUND with five speakers that transmit the full audio spectrum and one that transmits only bass. The five full-range speakers are positioned as front left, center, and right, and rear left and right. The bass speaker, or SUBWOOFER, is usually placed in front. See Fig. 253, p. 464. Compare 6.1, 7.1.

6.1 a format of SURROUND SOUND with six full-range speakers in the left front, center front, right front, left, right, and rear center positions, plus a SUBWOOFER for additional bass. Compare 5.1.

7-layer model see DATA COMMUNICATION.

7.1 a format of SURROUND SOUND with seven full-range speakers in the left front, center front, right front, left, right, left rear, and right rear posi-tions, plus a SUBWOOFER for additional bass. Compare 5.1.

8.3 filename a filename consisting of up to 8 letters or digits, a dot (period), and up to three more letters or digits, as in DOS and Windows 3.

10/100 (describing a network adapter) capable of operating at 10 or 100 megabits per second. See 10BASE-T; 100BASE-T.

10/100/1000 (describing a network adapter) capable of operating at 10, 100, and 1000 megabits per second. See 10BASE-T; 100BASE-T; 1000BASE-T.

10base-2 thinwire Ethernet; a type of Ethernet connection using thin coax-ial cable with BNC T-connectors, a bus topology, and a maximum data rate of 10 megabits per second. Cable segments can range from 2 feet (0.6 m) to 607 feet (185 m) in length. See ETHERNET; THINWIRE.

Usage note: In this and similar terms, 10 stands for the data rate in megabits per second; base means baseband (not modulated on a higher-frequency carrier); and 2 is the approximate maximum cable length in hundreds of meters. The hyphen is often left out.

10base-5 2

10base-5 thickwire Ethernet; a type of Ethernet connection using thick coaxial cable with special cable-piercing taps, a bus topology, and a maximum data rate of 10 megabits per second. Cable segments can range from 8.2 feet (2.5 m) to 1640 feet (500 m) in length. See ETHER-NET; THICKWIRE.

10base-F fiber-optic Ethernet; a type of Ethernet connection using fiber-optic cable and a maximum data rate of 10 megabits per second. Cables can be as long as 1.2 miles (2 km). See ETHERNET; FIBER OPTICS.

10base-T twisted-pair Ethernet using Category 3 or Category 5 cable and RJ-45 modular connectors, a star topology with hubs, and a maximum data rate of 10 megabits per second. Each cable can be up to 328 feet (100 m) long. However, because they are unshielded, these cables are somewhat subject to electrical noise if placed close to motors or fluo-rescent lights. See ETHERNET; CROSSOVER CABLE; CATEGORY 5 CABLE.

16-bit program a program that runs on Intel microprocessors using only the features of the 8088 or 80286, with 16-bit internal registers. Most DOS applications and many earlier Windows applications are 16-bit pro-grams. Contrast 32-BIT PROGRAM.

24-bit graphics graphical images that use 24 bits to represent each color, so that each color is made by mixing red, green, and blue, each of which is measured on a scale of 0 to 255, and a total of 16,777,216 colors is available. Often called “millions of colors.”

24  7 (or 24/7, 24-7) available 24 hours a day, 7 days a week.

32-bit program a program that uses the 32-bit internal registers and large memory capacity of the Intel 386, 486, Pentium, or other compatible micro-processor; generally faster than a 16-bit program doing the same computa-tion on the same CPU. Contrast 16-BIT PROGRAM. See also WIN32S.

32-bit Windows Microsoft Windows 95, NT, and their successors for the Pentium and related processors, as distinct from Windows 1.0–3.1 (apart from 32-bit add-ons) or Windows CE. See WINDOWS.

35-mm equivalent the focal length of lens, on a 35-mm film camera, that would cover the same field of view as a particular digital camera and lens. See CROP FACTOR; FOCAL LENGTH; ZOOM.

47 USC 227 the 1991 U.S. law that banned “junk faxing” (unsolicited advertising by fax). See JUNK FAX.

100base-F fast fiber-optic Ethernet, like 10base-F but with a maximum data rate of 100 megabits per second.

100base-T fast twisted-pair Ethernet using Category 5 cable and RJ-45 modular connectors; like 10base-T but with a maximum data rate of 100 megabits per second. Many network cards and hubs are compatible with

3 486

both 10base-T and 100base-T transmission. Thus, you can convert a 10base-T network to 100base-T component-by-component and switch to the higher speed when all the components have been modernized.

386 the first Intel microprocessor with 32-bit internal registers and good support for multitasking and extended memory; able to run Windows 95, but too slow for most present-day software. See MICROPROCESSOR.

403 FORBIDDEN HTTP error message indicating that the HTTP server is not permitted to read a file. This usually means that the owner of the web page has not set the correct permissions on the file. See PERMISSION.

404 NOT FOUND HTTP error message indicating that a web address is invalid. See DEAD LINK.

419 scam, 4-1-9 scam a form of fraud conducted through e-mail, usually from Nigeria, where it violates section 4-1-9 of the criminal code, hence the name.

The perpetrator sends out mass e-mail claiming to be a bank officer or government official who needs help sneaking some money out of the country and wants to use someone else’s bank account. In return, the vic-tim will get thousands or millions of dollars.

What actually happens is that the victim’s bank account is emptied, or the victim’s information is used for further fraud. Some victims have even been lured into traveling overseas without proper visas so that they could be trapped and blackmailed.

The 419 scam is so common that many active Internet users receive more than one solicitation per day. Newer versions of the scam no longer mention Nigeria, and many of them claim to offer lottery winnings, inheritances, or business deals.

486 an Intel microprocessor similar to the 386 but faster; predecessor of the Pentium. See MICROPROCESSOR



Specification Popular name Frequency Speed Compatible with

802.11a Wireless-A 5 GHz 54 Mbps Wireless-A
802.11b Wireless-B 2.4 GHz 11 Mbps Wireless-B
802.11g Wireless-G 2.4 GHz 54 Mbps Wireless-B, -G
802.11n Wireless-N 2.4 GHz 100 Mbps Wireless-B, -G, -N

802.11 4

802.11 (more fully, IEEE 802.11) a set of specifications for wireless net-working that give performance similar to 10base-T or 100base-T and implement Wi-Fi product compatibility standards (Table 1).

Note that the three 2.4-GHz specifications are downward compatible; that is, a Wireless-B computer will work in a Wireless-G or Wireless-N network. Of course, in that case, communication takes place at the lower speed of Wireless-B.

802.16 see WIMAX.

1394, 1394a, 1394b see FIREWIRE.

2000 see YEAR 2000 PROBLEM.

2600 a number used as an identifying code by groups of people who exchange detailed information about how to break into computers, tam-per with telephone systems, duplicate credit cards, and the like, whether for the purpose of preventing or encouraging these acts. There is a mag-azine (2600: The Hacker Quarterly), a newsgroup (alt.2600), and a variety of loosely organized local “2600” groups. See HACKER (definition 3); CRACKER; PHREAK.

The number 2600 is from the 2600-Hz control tone formerly used in telephone systems. The Atari 2600 video game machine is completely unrelated.

8088 the Intel microprocessor used in the original IBM PC (1981). It has 16-bit registers and an 8-bit external bus. See MICROPROCESSOR.

68000 the series of Motorola microprocessors originally used in the Apple Macintosh. See MICROPROCESSOR.

80286 the Intel microprocessor used in the IBM PC AT (1984). It is faster than the 8088 and supports extended memory but does not have 32-bit registers or the built-in ability to emulate multiple 8088s; for that reason, multitasking operating systems did not become common until the 386 was introduced. See MICROPROCESSOR.

80386, 80486 unofficial names for the Intel 386 and 486 microprocessors. See 386, 486, and references there.

5 π


α (alpha) the opacity of a layer in a graphical image. See ALPHA.

γ (gamma) a measure of the contrast of photographic film or the nonlin-earity of an electronically obtained image. See GAMMA.

μ (mu) abbreviation for micro- (one-millionth). See METRIC PREFIXES.

μC abbreviation for microcontroller.

μP abbreviation for microprocessor.

π (pi) the ratio of the circumference of a circle to its diameter, approxi-mately 3.14159. See PI.


The Greek Alphabet

A α alpha
B β beta
Γ γ gamma


Εεepsilon ( in some typefaces)

Ζ ζ zeta
Η η eta

theta ( in some typefaces)

Ι ι iota
Κ κ kappa
Λ λ lambda
Μ μ mu
Ν ν nu
Ξ ξ xi
Ο ο omicron

Ππpi ( in some typefaces)

Ρρrho ( in some typefaces)

Σσsigma ( at ends of words)

Τ τ tau
υ upsilon

Φφphi ( in some typefaces)

Χ χ chi
Ψ ψ psi
Ω ω omega

7 abs



1. abbreviation used in HTML to indicate an anchor, a link to another location. For an example, see HTML.

2. (on a digital camera) aperture-priority autoexposure, the mode in which the user sets the lens opening (f-ratio) and the camera chooses the exposure time; same as Av. Contrast P, TV, S.

A4 the standard size of typing paper everywhere except the United States, 210  297 mm, about 81⁄4  113⁄4 inches. American typing paper is 81⁄2  11 inches.

A4 is part of an ISO standard for paper sizes (chosen so that A0 paper (840  1189 mm) has an area of 1 square meter and each size can be cut in half to make the next smaller one. Thus, the area of a sheet of A4 paper is 1⁄16 m2). For table, see PAPER SIZES (ISO).

FIGURE 1. A4 paper is longer and narrower than letter size

AAC Advanced Audio Coding, an audio compression format newer and more efficient than MP3, used internally by iTunes and Nintendo Wii. See www.mpeg.org/MPEG/aac.html.

ABC Atanasoff Berry Computer, a machine developed in 1939 at Iowa State University by John Atanasoff and Clifford Berry for solving equa-tion systems. Although it did not allow for stored programs, it was an important predecessor of the ENIAC and other digital computers.

abort to cancel an action or command.

Abort, Retry, Fail? an error message displayed by DOS and similar oper-ating systems when a disk is unreadable or some other input or output operation is physically impossible. An earlier version said, “Abort, Retry, Ignore?”

abs the function that calculates absolute value in many programming lan-guages and on scientific calculators. It converts negative numbers to positive while leaving positive numbers unchanged. For example,

abs(37) = 37; abs(–37) = 37; abs(–2.5) = 2.5; abs(0) = 0.



absolute address

absolute address
1. a fixed location in the computer’s memory. See
2. in a spreadsheet program, a cell address that refers to a fixed location that will not change when a formula is copied to another location. In Excel, absolute addresses are indicated by placing a dollar sign before the column and row indicator. For example, if the formula 2*$D$7 is entered into a cell, then $D$7 is an absolute address. If this formula is copied to another cell, the address $D$7 will not change. Contrast RELA-TIVE ADDRESS.
3. See

absolute URL a URL that contains the full address, identifying the machine, directory, and file. For example, if a web page contains the link:

<a href=”http://www.census.gov/2010census/about_2010_census/”>

it will find about _2010_census in the directory 2010census at the com-puter labeled www.census.gov. Contrast RELATIVE URL.


1. a summary of a document or file. For example, in Java programming, a JAR FILE contains class files together with an encrypted abstract (sum-mary) calculated with a kind of hash function. If one of the class files is tampered with, the hash function calculated from the downloaded files will not match the hash function in the abstract, so the verifier will not allow the class to load. See also MANIFEST.

2. not tied to a specific pre-existing example. For example, an abstract data type is one that does not correspond exactly to anything in the archi-tecture of the computer; instead, it is declared by the programmer to suit the purposes of the program.

In object-oriented programming, a class is declared abstract if there will not be any data or methods specific to that class; instead, it is to be used as a superclass for other classes that will have specific data. An abstract class cannot be instantiated, but other classes can extend it.

accelerator a device that makes an operation run faster. For example, a graphics accelerator is a card that contains built-in circuits for perform-ing graphics operations, allowing the system to render graphics more quickly than would be the case if the microprocessor bore the entire load.

accents marks added to letters (as in é è ê ë) to indicate differences of pro-nunciation; said to have been introduced by Aristophanes of Byzantium c. 200 B.C. to preserve the pitch accent of ancient Greek, which was dying out. The only major languages that do not require accents are English and Latin.

Most computer software treats a letter with an accent as a single char-acter. More sophisticated systems represent the accent and the letter sep-arately, so that any accent can be put on any letter. See ANSI.

9 accessibility

acceptable-use policy a policy established by the owner of a computer sys-tem, or by an Internet service provider, concerning acceptable use of the computer and network facilities. Acceptable-use policies should gener-ally include the following points:

1. Users are accountable for what they do. Deliberate snooping, harassment, or interference with other users will not be tolerated, nor will any deliberate unauthorized activity.

2. The computer shall be used only for its intended purposes. For example, you generally can’t use your employer’s computer to run another business on the side; nor can you run private money-making schemes on a computer owned by a state university. Employees are accountable for how they use their time at work.

3. Passwords must be kept secret. See PASSWORD.

4. The service provider has the right to suspend accounts that are being misused. People accused of misconduct have the right to a fair hearing.

5. Users must abide by the acceptable-use policies of newsgroups and other electronic discussion forums, which are mostly paid for by other people. On the Internet you are always someone’s guest.

6. Chain letters and mass e-mailing are expensive, unwelcome, and generally not permitted. The correct way to reach a wide audience is to use an appropriate newsgroup.

7. Cyberspace is not above the law. Practices that are illegal in the real world, such as forgery, gambling, obscenity, and threatening or inciting violence, are still illegal when you do them on the computer.

8. Losing an account is not necessarily the only penalty for miscon-duct. The service provider cannot shield users from criminal or civil liability when they break laws or deliberately harm others. Really destructive computer abusers generally have several accounts and must be stopped by other means.

Access a powerful, highly programmable RELATIONAL DATABASE marketed by Microsoft as part of the Office suite of products.

access control list in Windows, the list of which users or groups are allowed to use a file, directory, or device. See CACLS.

access provider see INTERNET SERVICE PROVIDER.

access time the amount of time needed by a memory device to transfer data to the CPU.

accessibility the measure of how fully a computer product can be used by people of varying abilities. For example, a blind computer user visiting a web page may use speech synthesis software to read the page aloud. A web site where images all have alternate text descriptions is more acces-sible than a web site without such tags. See also WAI.

account 10

account authorization to use a computer or any kind of computer service, even if free of charge. An account consists of an identifying name and other records necessary to keep track of a user. Sometimes an account belongs to another computer or a computer program rather than a human being.

accounting system software that reads in data for transactions and gener-ates income statements, balance sheets, and related financial reports. See also QUICKEN.

accumulator the register where a computer stores the result of an arith-metic operation. For example, in 8086 assembly language, the instruc-tion ADD AX,10 means “Add 10 to the number in the accumulator, and leave the result there.” Some computers can use more than one register as an accumulator. See COMPUTER ARCHITECTURE; ASSEMBLY LANGUAGE.


ACM (Association for Computing Machinery) a worldwide association of computer professionals headquartered in the United States. Their web address is www.acm.org.

ACPI (Advanced Configuration and Power Interface) a set of standard hardware/software interactions that give the operating system the ability to direct power management of hardware devices. For example, a com-puter with ACPI can turn itself off under software control as the last step in shutting down the operating system.

acquire to obtain a file (for editing) from a scanner or a camera. Similar to IMPORT, except that the image is not coming from a file.

Acrobat software from ADOBE SYSTEMS, INC., for creating and reading PDF (Portable Document Format) files. Acrobat Reader is a browser plug-in available free from Adobe’s web site (www.adobe.com) that enables users to view and print PDF files that they receive from others. The full version of Acrobat is a powerful multi-use utility designed to facilitate annotation and distribution of digital documents. With Acrobat, com-ments and highlights can be added to documents. It’s possible to perform minor text edits, although large changes to page layout are not possible. Forms can be made interactive. Multiple .pdf documents can be com-bined or pages may be extracted into separate files. Acrobat also includes the ability to add a secure digital signature to .pdf documents.
See PDF.

acronym a word formed from the initial parts of other words. For example, BASIC stands for Beginner’s All-Purpose Symbolic Instruction Code.
See also TLA.


1. to choose a window in which you want to type. This is done by mov-ing the mouse pointer into the window and clicking one button. In some

11 ActiveX

operating systems you must click on the window’s title bar. See WINDOW. 2. to start a piece of software by double-clicking on its name or icon.
3. to make a software product usable by informing the manufacturer that it has been installed and obtaining an activation code. This can be done on line or by making a telephone call. See REGISTRATION (definition 1).

active color the color currently selected (in a painting or drawing pro-gram). Whatever tool is being used will paint or draw in the active color.

Active Desktop in Windows, the ability to use a WEB PAGE as the desktop, i.e., the screen itself, not just as one of the programs running on it. This makes it easy to display a web page that is constantly updated, such as weather or stock price information, without having to start and run a

active matrix a type of liquid crystal display (LCD) that produces higher contrast than earlier passive-matrix displays by incorporating transistors into the LCD matrix.

active window the window currently in use, the one in which the user is typing, drawing, or making menu choices (see Figure 2). There can only be one active window at a time. See WINDOW; ACTIVATE.

FIGURE 2. Active window

ActiveX a marketing name used by Microsoft for many types of software components implemented in the COM (Component Object Model) architecture (see COM).

An ActiveX control is a small piece of software designed to be used as part of a larger one. Some ActiveX controls are simply object libraries or subroutine libraries used by programmers—a more sophisticated kind of DLL. Others work more like Java applets (see APPLET).

At one time it was common to include ActiveX controls in web pages, as programs to be executed on the client computer, but because of secu-rity risks, many web browsers no longer accept them.

actor 12

actor in computer animation, any object that moves in a specified manner along a path, whether or not it represents a human being. Even a bounc-ing ball is an actor.

actual parameter the value actually passed to a function or procedure in a programming language. For example, if you compute ABS(X) and the value of X is –2.5, then –2.5 is the actual parameter of ABS. See FORMAL PARAMETER; PARAMETER.


Ada a programming language developed in the late 1970s for the U.S. Department of Defense. It is named for Augusta Ada Byron, Countess of Lovelace, who worked with Babbage’s mechanical calculator in the nineteenth century.

Ada subprograms can be compiled separately and linked together before execution. In the sample program, the with and use statements specify that this program uses a library of precompiled subroutines called I_O_PACKAGE.

Much of the original motivation for designing Ada was the need for a better language for real-time programming, that is, programming com-puters to control automatic or semiautomatic equipment. Toward this end, Ada allows the programmer to create multiple tasks that run con-currently (see TIMESHARING) to pass signals from one task to another and to introduce controlled time delays.

with I_O_PACKAGE; procedure FACTORIAL is


--This program reads a number and --computes its factorial.



FACT := 1;

for COUNT in 2..NUM loop FACT := FACT * COUNT;

end loop;

PUT(”The factorial of ”); PUT(NUM); PUT(” is ”); PUT(FACT);


FIGURE 3. Ada program

adaptive tech

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