Encyclopedia of Computer Science and Technology

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itwise operations 51in terms of bytes. A byte is 8 bits or binary digits, whichamounts to a range of from 0 to 255 in terms of decimal (base10) numbers. A byte is thus enough to store a small integeror a character code in the standard ASCII character set(see character). Common multiples of a byte are a kilobyte(thousand bytes), megabyte (million bytes), gigabyte (billionbytes), and occasionally terabyte (trillion bytes). The actualnumbers represented by these designations are actually somewhatlarger, as indicated in the accompanying table.Further Reading“How Bits and Bytes work.” Available online. URL: http://www.howstuffworks.com/bytes.htm. Accessed April 22, 2007.One byte in memory can store an 8-bit binary number. Just as eachplace to the left in a decimal number represents the next higherpower of 10, the places in the byte increase as powers of 2. Here theplaces with 1 in them add up to a total decimal value of 213.With regard to computer architectures the numberof bits is particularly relevant to three areas: (1) The sizeof the basic “chunk” of data or instructions that can befetched, processed, or stored by the central processing unit(CPU); (2) The “width” of the data bus over which data issent between the CPU and other devices—given the sameprocessor speed, a 32-bit bus can transfer twice as muchdata in a given time as a 16-bit bus; and (3) The width of theaddress bus (now generally 32 bits), which determines howmany memory locations can be addressed, and thus themaximum amount of directly usable RAM.The first PCs used 8-bit or 16-bit processors, whiletoday’s PC processors and operating systems often use 32-bits at a time, with 64-bit processors now entering the market.Besides the “width” of data transfer, the number of bitscan also be used to specify the range of available values.For example, the range of colors that can be displayed bya video card is often expressed as 16 bit (65,536 colors) or32 bit (16,777,777,216 colors, because only 24 of the bits areused for color information).Since multiple bits are often needed to specify meaningfulinformation, memory or storage capacity is often expressedbitwise operationsSince each bit of a number (see bits and bytes) can holda truth value (1 = true, 0 = false), it is possible to use individualbits to specify particular conditions in a system, andto compare individual pairs of bits using special operatorsthat are available in many programming languages.Bitwise operators consist of logical operators and shiftoperators. The logical operators, like Boolean operators ingeneral (see Boolean operators), perform logical comparisons.However, as the name suggests, bitwise logical operatorsdo a bit-for-bit comparison rather than comparing theoverall value of the bytes. They compare the correspondingbits in two bytes (called source bits) and write result bitsbased on the type of comparison.The AND operator compares corresponding bits andsets the bit in the result to one if both are one. Otherwise, itsets it to zero.Example: 10110010 AND 10101011 = 10100010The OR operator compares corresponding bits and setsthe bit in the result to one if either or both of the bits areones.Example: 10110110 OR 10010011 = 10110111The XOR (“exclusive OR”) operator works like ORexcept that it sets the result bit to one only if either (notboth) of the source bits are ones.Example: 10110110 XOR 10010011 = 00100101The COMPLEMENT operator switches all the bits totheir opposites (ones for zeroes and zeroes for ones).Example: COMPLEMENT 11100101 = 00011010Measurement Number of Bytes examples of Usebyte 1 small integer, characterkilobyte 2 10 1,024 RAM (PCs in the 1980s)megabyte 2 20 1,048,576 hard drive (PCs to mid-1990s)RAM (modern PCs)gigabyte 2 30 1,073,741,824 hard drive (modern PCs)RAM (latest PCs)terabyte 2 40 1,099,511,627,776 large drive arrays
52 blogs and bloggingThe shift operators simply shift all the bits left (LEFTSHIFT) or right (RIGHT SHIFT) by the number of placesspecified after the operator. Thus00001011 LEFT SHIFT 2 = 00101100and00001011 RIGHT SHIFT 2 = 00000010 (bits that shift offthe end of the byte simply “drop off” and are replaced withzeroes).While we have used words in our general description ofthese operators, actual programming languages often usespecial symbols that vary somewhat with the language. Theoperators used in the C language are typical:& AND| OR^ Exclusive OR~ Complement>> Right Shift
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Encyclopedia ofComputer scienceand
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C on t e n t sAcknowledgmentsivintr
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I n t r od u c t ion to t h eR e v
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Introduction to the Revised Edition
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Page 19 and 20: Algolgrammar of the data-descriptio
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Page 23 and 24: 10 Amdahl, Gene MyronShanahan, Fran
Page 25 and 26: 12 analog and digitalhistory, bring
Page 27 and 28: 14 Andreessen, MarcCompleted in 193
Page 29 and 30: 16 animation, computerAndreessen tr
Page 31 and 32: 18 APLAPL (a programming language)T
Page 33 and 34: 20 application program interfacerat
Page 35 and 36: 22 application softwareURL: http://
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Page 39 and 40: 26 artificial intelligenceby tradit
Page 41 and 42: 28 artificial lifewriters such as V
Page 43 and 44: 30 Atanasoff, John VincentAtanasoff
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Page 47 and 48: 34 awkthose found in C. There are a
Page 49 and 50: 36 backup and archive systemsthe ec
Page 51 and 52: 38 Backus-Naur formBackus-Naur form
Page 53 and 54: 40 basic input/output systemdecisio
Page 55 and 56: 42 Bell Laboratoriesand the early a
Page 57 and 58: 44 Bezos, Jeffrey P.use if it is to
Page 59 and 60: 46 bioinformaticsand a hierarchy of
Page 61 and 62: 48 biometricsvariety of biometric s
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Page 70 and 71: oadbandTechnically, broadband refer
Page 72 and 73: Brooks, Rodney 59such as Flickr and
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Page 79 and 80: 66 CTotal = Total + 1;Total += 1;To
Page 81 and 82: 68 C++While attracted to the advant
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Page 85 and 86: 72 cascading style sheetsMojave Des
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Page 91 and 92: 78 central processing unitcentral p
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Page 105 and 106: 92 codecMurcah, Mike, Anne Prince,
Page 107 and 108: 94 COMcommon object request broker
Page 109 and 110: 96 compilersuch as a keyword (reser
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102 computer forensicsa device proc
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104 computer graphicsthe same time,
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106 computer industryso on). By cre
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108 computer industrypackages serve
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110 computer virus• What is the b
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112 computer visionsense on the par
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114 conferencing systemsFeldman, Mi
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116 cookiesunlike most traditional
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118 CORBA“activation” or “val
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120 CraigslistMano, M. Morris, and
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122 CRMtasks can be assigned to dif
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124 cyberneticsMany issues regardin
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126 cyberstalking and harassmentThe
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DdataToday the term data is associa
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130 database administrationsignal m
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132 database management systemMicro
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134 data compressionlocal network,
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136 data securityparticular purpose
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138 data typeswhile a list has one
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140 Dell, Inc.User Interface—The
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142 design patternsdesign patternsD
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144 device driverOne Laptop per Chi
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146 digital cashcould be worked bac
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148 digital dashboardThe ownership
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150 Dijkstra, Edsger W.discs. A big
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152 disaster planning and recoveryT
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154 distributed computingAnother wa
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156 DNSCSCUCVCXCYCZDEDJDKDMDODZECEE
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158 documentation of program codewi
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160 document modelSociety for Techn
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162 DRMresearchers. For example, Al
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164 DVRMPEG file) that is fully com
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166 e-books and digital librariesha
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168 e-commerceRemington Rand. Worki
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170 education and computersApplicat
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172 e-governmentlenges face educati
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174 Electronic Artsteaching softwar
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176 e-maillanguages. However this c
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178 employment in the computer fiel
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180 encapsulationconsist of a combi
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182 Engelbart, DouglasEngelbart, Do
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184 entrepreneurs in computinganaly
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186 error correctionSalvendy, Gavri
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188 expert systemsAnatomy of an Exp
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190 Feigenbaum, Edwardhttp://hissa.
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192 file serverdata integrity. Vers
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194 film industry and computingImpl
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196 firewallcontrolled by a state t
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198 flash and smart mobs(or even pr
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200 flowchartused to hold data. The
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202 FORTRANearly days of microcompu
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204 fuzzy logicdefining and arrangi
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206 Gates, William, IIIGame console
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208 Geographical Information System
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210 Google• downward wage pressur
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212 government funding of computer
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214 graphics formatsof objects so t
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216 grid computingoff. By 2000, vir
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218 Grove, Andrew S.Cavalancia, Nic
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220 handwriting recognitionand othe
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222 hard disk• remote surgery, wh
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224 health, personalTo search a has
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226 history of computingFurther Rea
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228 history of computingThe most st
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230 home officeFacing vigorous comp
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232 HTML, DHTML, and XHTMLFurther R
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234 hypertext and hypermediaImpleme
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236 IBM PCFurther ReadingBashe, Cha
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238 identity theftfrom meetings to
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240 information retrievalinvasion o
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242 information warfareShannon foun
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244 installation of softwareinstall
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246 internationalization and locali
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248 Internettransmission of a messa
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250 Internet censorshipDunaev, Serg
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252 interpreterconsidered to be ISP
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JJavaJava is a computer language si
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256 JavaScriptIn 2006 Sun Microsyst
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258 Jobs, Steven Paulan enthusiasti
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260 journalism and the computer ind
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262 Joy, Billwho will be unable to
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264 kernelcould send a message to t
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266 knowledge representationattende
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268 Kurzweil, RayFurther ReadingFre
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LLAN See local area network.languag
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272 laptop computerapplications for
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274 Lessig, Lawrencepleadings and o
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276 library, programadditional copi
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278 linguistics and computingIn his
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280 LISPA Linux system running Open
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282 list processinga rich variety o
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284 Logoa checksum, and two special
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286 LuaNext CharValHere Char$ is a
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288 macroMacDailyNews. Available on
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290 mainframeMaes has participated
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292 map information and navigation
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294 mashupsbefore you buy” softwa
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296 Mauchly, John WilliamMoving fro
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298 measurement units used in compu
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300 medical applications of compute
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302 memory managementTom’s Hardwa
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304 microprocessorMicroprocessor de
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306 Microsoft .NETbrowser had broug
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308 Microsoft WindowsIntroduced in
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310 middlewareBott, Ed, Carl Sieche
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312 minicomputer“How Military Rob
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314 Mitnick, Kevin D.———. “
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316 molecular computingdevice could
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318 Moore, Gordon E.only one gun, w
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320 Motorola CorporationMotorola Co
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322 multimediaa maximum of 640 kB o
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324 multitasking“local” memory
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326 music and video distribution, o
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328 music and video players, digita
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330 natural language processingplac
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332 Net Neutrality• Do not post b
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334 networkGoogle Groups, is the be
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336 neural networkwebmd.com/stroke/
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338 numeric dataselect customer whe
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340 object-oriented programmingPARC
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342 Omidyar, Pierreprovided for typ
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344 online advertisingnew structure
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346 online gamblingand agencies suc
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348 online investingThe close and g
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350 online servicesand drugs. The s
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352 open-source movementopen-source
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354 operators and expressionsOperat
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356 optical computingA more general
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PPage, Larry(1973- )AmericanEntrepr
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360 parallel porthis work. Papert l
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362 PascalLevine, John R., Tony Mas
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364 PDATheodoridis, Sergios, and Ko
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366 personal computerConway, Damian
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368 personal information managercom
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370 phishing and spoofing“Phishin
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372 PHPeach of the three RGB colors
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374 Plug and PlayImpact of the Lang
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376 pointers and indirectionA point
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378 popular culture and computingHo
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380 presentation softwareDeclineBy
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382 printersarray of magnetically c
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384 procedures and functionsagencie
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386 programming as a professioncalc
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388 programming languagesprogrammer
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390 PrologGiven the scope and pace
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392 punched cards and paper tapepun
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Qquality assurance, softwareModern
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396 queueIn an empty queue, the hea
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RRAID (redundant array of inexpensi
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400 recursionand with the potential
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402 regular expressioncompetitive a
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404 reverse engineeringA similar ap
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406 RFIDParts of an RFID system. De
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408 risks of computingHafner, Katie
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410 roboticsMac. The MIT computer s
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412 RPGHenderson, Harry. Modern Rob
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414 Rubya file, as with many script
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416 satellite Internet serviceFurth
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418 science fiction and computingre
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420 scientific computing applicatio
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422 search engineuseful tools for m
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424 semantic WebSearch Engine Watch
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426 Shannon, Claude E.Service-orien
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428 shellPC-Write as a full-feature
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430 Simonyi, Charlestests for the p
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432 singularity, technologicalToget
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434 smart buildings and homesThis m
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436 smartphonestore a hundred or mo
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438 SOAPPogue, David. iPhone: The M
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440 social networkingThere continue
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442 software agentLife could be stu
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444 software piracy and counterfeit
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446 sorting and searching• Discma
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448 sound file formatsapproach, and
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450 Spafford, Eugene H.and computer
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452 spreadsheetSpeech recognition b
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454 SQLFurther Reading“Antispywar
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456 stackstackOften a temporary sto
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458 Stoll, CliffordCharles Babbage
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460 structured programmingsuited fo
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462 supply chain managementApplicat
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464 system administratorsystem admi
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Ttablet PCAs the name suggests, a t
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468 TclHaylor, Phil. Computer Stora
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470 technical supportIPv6 Informati
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472 technology policyDuring the 198
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474 telepresence• elimination of
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476 text editortyping commands into
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478 touchscreencode. This would mea
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480 trends and emerging technologie
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482 Turkle, SherryFurther ReadingHe
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Uubiquitous computingTraditionally
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486 USB% who | awk ' { print $1 }'H
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488 user groupsGarofoli, Joe. “Us
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VvariableVirtually all computer pro
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492 videoconferencingconsequence wa
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494 virtualizationused as an expres
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496 VoIPtank crews and even individ
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498 von Neumann, JohnJohn von Neuma
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WWales, Jimmy(1966- )AmericanIntern
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502 Web 2.0 and beyond“Web 2.0”
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504 webcamabout a 75 percent market
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506 Web page design• fluency in t
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508 Web servicesWhen a user types i
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510 Wiener, Norbertcomplexity . . .
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512 wikis and WikipediaWiki softwar
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514 Wirth, NiklausMobile Wireless N
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516 word processingto promote netwo
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518 World Wide WebBy the beginning
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XXMLSeveral markup languages have b
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YY2K problemSherlock Holmes once re
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524 YouTube• excessive time spent
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526 Zuse, Konradneeded would make t
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528 Appendix IRed Herring: The Busi
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530 Appendix IIing company (CTR) in
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532 Appendix II• Users of the new
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534 Appendix II••ibm developed
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536 Appendix II• Bill Gates and P
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538 Appendix II• A consortium cal
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540 Appendix II• Apple released o
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Appendix IIISome Significant Awards
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544 Appendix III1993 Juris Harmanis
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546 Appendix III1972 Paul E. Dirkse
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548 Appendix IIIJohn W. BackusRober
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550 Appendix IIIsity of Manchester
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552 Appendix IIIthereby enhancing A
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554 Appendix IVInternational Webmas
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556 IndexAnalytical Engine 35-36, 3
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558 Indexdata communications over13
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560 Indexgraphics in 106, 194haptic
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562 IndexDertouzos, Michael L. 141D
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564 IndexFFacebook 16, 440-441, 487
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566 IndexIDNA (Internationalizing D
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568 Indexin open-source movement352
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570 IndexMinard, Joseph 239mind 92-
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572 IndexOnStar 71ontologies and da
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574 Indexin object-orientedprogramm
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576 Indexsequential calculator 5ser
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578 Indexterminals in 475-476user i
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580 Indexdatabases in 132developmen
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