Encyclopedia of Computer Science and Technology

120 CraigslistMano, M. Morris, and Charles Kime. Logic and Computer DesignFundamentals. 4th ed. Upper Saddle River, N.J.: Prentice Hall,2007.Stokes, Jon. Inside the Machine: An Illustrated Introduction to Microprocessorsand Computer Architecture. San Francisco: NoStarch Press, 2006.The CPU uses the Instruction Pointer (IP) to keep track of theaddress of the next instruction in memory, which is stored in theInstruction Register (IR). The Address Register (AR) and DataRegister (DR) perform a similar function with program data. Datacan also be moved between main memory and the CPU’s registers,which are special fast-retrieval memory locations. Instructions aredecoded by the control unit and passed to the arithmetic Logic Unit(ALU) for execution.such as a result being negative. Based on the instructionsand signals, the CPU can skip over some instructions, jumpingto another location in the program.The main memory or RAM (random access memory)contains both the program instructions and the data beingused by the program, which in turn can be read from adisk or other medium or written back to storage. The effectivespeed of the system is derived not only from the clockspeed but from the speed at which data travels over the systembus, a set of wires that each carry one data bit, as wellas the operating speed of the memory chips themselves (seeclock speed and bus).The access of programs to the CPU is controlled in turnby the operating system. Modern operating systems sharethe CPU with several running programs, doling out executiontime according to a scheduling algorithm that takesinto account the possible special priority of some programs(see multitasking).Further ReadingBrain, Marshall. “How Microprocessors Work.” Available online.URL: http://computer.howstuffworks.com/microprocessor.htm.Accessed June 30, 2007.CraigslistSome of the most successful Web services involve just oneor two basic changes in a traditional business or socialmodel. Online auctions, for example, came from the realizationthat the auctioneer and auction house could beeliminated and a platform provided by which people couldbuy from or sell to one another directly. (The platform, ofcourse, does have to include such things as listing policies,payment methods, and feedback systems.)Craigslist has done for the newspaper “personal” ad andlaundromat bulletin board what eBay has done for auctions.It was founded in 1995 by Craig Newmark, a San FranciscoBay Area software developer who saw a need for an onlineforum for news about local events. The “list” part of Craigslistreflects its origin as an e-mail list.News about the list spread rapidly in Newmark’s milieuof well-connected professionals, and the volume of postingsgrew correspondingly large. Furthermore, many peoplebegan to post things other than event listings—includingjob openings, for which Newmark soon set up a separatecategory on the list. As the number and kinds of postingsgrew, the mailing list format became unwieldy, so Newmarkand some volunteers put together a Web interface thatusers could use to browse the various categories. By 2000Craigslist.org had become a full-time job for Newmark andnine employeesCraiglist’s Web site is organized by community, includingU.S. states and cities and a variety of other countriesand international cities. Each local site is further dividedinto sections such as community activities (including peopleseeking or providing childcare or sharing rides), personalads (seeking relationships), housing (mostly rentals), jobs,services, items for sale, and a variety of discussion forums.As of 2007 Craigslist had 24 employees. The site is nearlycompletely free of charge, with revenue coming only frompaid job listings and apartment broker listings in selectedcities. The site’s popularity has been impressive, with morethan 5 billion page views, 10 million visitors, and over 10million classified ads per month.Newmark and CEO Jim Buckimaster have suggestedthat they have little interest in either turning Craigslistinto a public company or “going commercial” and tappingwhat many observers consider to be much greater revenuepotential.Problems and IssuesCraiglist’s success has raised some issues. In 2004 eBaybought a 25 percent stake in the company, leading somesupporters to worry about pressure to raise more revenueby carrying banner ads or charging for posting on the site.However, as of 2008 the site remains free to users.