Encyclopedia of Computer Science and Technology

CPU 119In recent years the U.S. Department of Homeland Securityhas apparently been developing more sophisticateddata-mining and pattern-recognition programs (see biometricsand data mining). One is called ADVISE, or Analysis,Dissemination, Visualization, Insight, and SemanticEnhancement. This at least suggests an attempt not to simplyfind matches between e-mail, online postings, or othertextual data, but to construct profiles of a person’s activityand/or intentions, which could presumably then be comparedwith terrorist or criminal profiles.Surveillance or wiretapping of specific individuals alsoraises legal issues, particularly with recent revelations ofso-called warrantless wiretaps. Officials have claimed thatthere are relatively few such cases (perhaps fewer than 100per year), but the Bush administration’s claim that it didnot need to follow Foreign Intelligence Surveillance Act(FISA) procedures raised considerable controversy, and acourt decision forced the administration to seek affirmationof its powers by Congress.Intelligence officials argue that existing FISA proceduresare too cumbersome to deal with the Internet. Oldstylewiretapping involved specific telephone instrumentsand lines, but on the Internet the routing of information isconstantly changing, and a person may use several differentdevices and types of communication. Thus it is argued thatthe warrant must be broad enough to apply to the person,not a particular means of communication. It is also arguedthat the global nature of the network also means that distinctionsabout whether persons are inside or outside of theUnited States may no longer be as relevant.Privacy and civil liberties advocates tend to agree thatsome updating of warrant procedures to deal with moderntechnology is necessary, but they point to secretivenessand lack of effective legal oversight resulting in a lackof accountability for government surveillance programs.This concern has also been fueled by a succession of revelationsthat surveillance programs are more extensivethan previously thought. (This includes the involvementof telecommunications and Internet service providersand the use of FBI “national security letters”—essentiallysecret subpoenas.)Coordinating EffortsBesides the gathering and analysis of intelligence, computerapplications are used in the intelligence and counterterrorismcommunity for many of the same functions foundin any large enterprise. These applications include e-mail,personal information management, collaborative creationor review of documents, scheduling and project management,and so on.Intelligence agencies are even adopting some popularemerging Web technologies. First came Intellipedia, a classifiedversion of Wikipedia serving as a knowledge basefor intelligence professionals (see wikis and Wikipedia).In late 2007 the director of national intelligence (DNI)launched A-Space, which includes Intellipedia, while addingother extensive databases, online office facilities (similarto Google Apps), and even blogs and a MySpace-likecomponent (see social networking).Further ReadingDerosa, Mary. Data Mining and Data Analysis for Counterterrorism.Washington, D.C.: Center for Strategic & International Studies,2004.Hoover, J. Nicholas. “U.S. Spy Agencies Go Web 2.0 in Effortto Better Share Information.” InformationWeek, August 23,2007. Available online. URL: http://www.informationweek.com/story/showArticle.jhtml?articleID=201801990. AccessedSeptember 10, 2007.Lichtblau, Eric. “F.B.I. Data Mining Reached beyond Initial Targets.”New York Times, September 9, 2007. Available online.URL: http://www.nytimes.com/2007/09/09/washington/09fbi.html. Accessed September 10, 2007.Miller, Greg. “Spy Chief Reveals Details of Operations.” Los AngelesTimes. Available online. URL: http://www.latimes.com/news/nationworld/nation/la-na-intel23aug23,0,6229712.story?coll=la-home-center. Accessed September 10, 2007.Mohammed, Arshad, and Sara Kehaulani Goo. “GovernmentIncreasingly Turning to Data Mining.” Washington Post,June 15, 2006, p. D03. Available online. URL: http://www.whisperingwires.info/. Accessed September 10, 2007.National Research Council. Information Technology for Counterterrorism:Immediate Actions and Future Possibilities. Washington,D.C.: National Academies Press, 2003.Taipale, K. A. “Whispering Wires and Warrantless Wiretaps: DataMining and Foreign Intelligence Surveillance.” Bulletin onLaw & Security, spring 2006. Available online. URL: http://www.whisperingwires.info/. Accessed September 10, 2007.CPUThe CPU, or central processing unit, is the heart of a computer,the place where data is brought in from input devices,processed, and sent to output devices. (This article describesthe CPU from the point of view of desktop micromputers,where it is a single large silicon chip and supporting chips;see mainframe for a discussion of that earlier architecture,microprocessor for desktop and portable CPUs, and chipand chipset for physical design of components.)The CPU consists of two major parts. The arithmeticlogicunit performs arithmetic or logical operations on pairsof numbers brought in from memory and stored in speciallocations called registers (see arithmetic logic unit). Forexample, the CPU can add a value from main memory toa value stored in a register and store the result back intomemory. In addition to addition, subtraction, multiplication,and division, the CPU can logically compare the individualbits in two values, performing such operations asAND, where the result is 1 only if both bits are ones, or OR,where the result is 1 if either bit is one. The power of a CPUis measured either in the number of clock cycles that driveit each second (see clock speed) or the number of standardinstructions it can execute in a second. For modern PCs,clock speeds range into the billions of cycles per second(gigahertz) and millions of instructions per second (mostinstructions take more than one cycle to be completed).The other key part of the CPU is the control unit, whichdetermines when (and which) instructions will be executed.Operations to be performed are specified by instruction valuesthat are the lowest level representation of program code,sometimes called machine code. An index register is usedto keep track of the current instruction. As instructions areprocessed, control signals can indicate special conditions,