Encyclopedia of Computer Science and Technology

284 Logoa checksum, and two special layers that interface with thediffering ways that Ethernet and token ring networks physicallyhandle the packets.The low-level processing of data packets must also beinterfaced with the overall operating system so that, forexample, a user on a desktop PC can “see” folders and fileson the file server and whole files can be transferred betweenserver and desktop PC. From the 1980s to the mid-1990sthe most common LAN operating system for DOS and laterWindows-based PCs was Novell Netware, while Macintoshusers used AppleTalk. Later versions of Windows (notablyWindows NT) then incorporated their own networkingsupport, and Netware use declined somewhat.The tremendous popularity of the Internet (particularlythe Web) starting in the mid-1990s propelled the Internetprotocol (see tcp/ip) into the forefront of networking.Today’s business and home computers use essentially thesame tools to connect to the global Internet and to oneanother. (The term Intranet, once used to distinguish localTCP/IP networks from the Internet, is now pretty muchobsolete.)Meanwhile, the technologies used to implement thisuniversal networking have proliferated. While the Internetis most commonly delivered to homes and businessesvia wires (see cable modem and dsl), wireless networkinghas replaced cable for many local networks, including mosthome networks (see Wireless and mobile computing),with the hub of the network being an inexpensive routerand wireless access point.Further ReadingBriere, Danny, Pat Hurley, and Edward Ferris. Wireless Home Networkingfor Dummies. Hoboken, N.J.: Wiley Publishing, 2006.Komar, Brian. Sams Teach Yourself TCP/IP Networking in 21 Days.2nd ed. Indianapolis: Sams, 2002.Lowe, Doug. Networking for Dummies. Hoboken, N.J.: Wiley Publishing,2007.Spurgeon, Charles. Ethernet: The Definite Guide. Sebastapol, Calif.:O’Reilly Media, 2000.Tittel, Ed, Earl Follis, and James E. Gaskin. Networking with Net-Ware for Dummies. 4th ed. Foster City, Calif.: IDG Books,1998.LogoLogo is a derivative of LISP (see lisp) that preserves much ofthat language’s list processing and symbolic manipulationpower while offering simpler syntax, easier interactivity,and graphics capabilities likely to appeal to young people.Logo has often been used as a first computer language forstudents in elementary and junior high school grades. AsHarold Abelson noted in his Apple Logo primer in 1982,“Logo is the name for a philosophy of education and a continuallyevolving family of programming languages that aidin its realization.”Logo was developed starting in 1967 by educator SeymourPapert and his colleagues at Bolt, Beranek and Newman,Inc. Papert, a mathematician and AI pioneer, hadbecame interested in devising an education-oriented computerlanguage after working with developmental psychologistJean Piaget. Papert focused particularly on Piaget’semphasis on “constructivism”—the idea that people learnmainly by fitting new concepts into an existing frameworkbuilt from the experience of daily life. Papert came tobelieve that abstract computer languages such as FORTRANor even BASIC were hard for children to assimilate becausetheir algebraic formulas and syntax had little in commonwith daily activities such as walking, playing, drawing, ormaking things.For example, most computer languages implementgraphics using statements that specify screen points usingCartesian coordinates (X, Y). A square, for example, mightbe drawn by statements such as:PLOT 100, 100LINETO 150, 100LINETO 150, 150LINETO 100, 150LINETO 100, 100While familiarity with the coordinate system eventuallyallows one to visualize this operation, it is far from intuitive.Papert, however, includes a “turtle” in his Logo language.The turtle was originally an actual robot that couldbe programmed to move around; in most systems today it isrepresented by a cursor on the screen. As the turtle moves,it uses a “pen” to leave a “trail” that draws the graphic.With turtle commands, a square can be drawn by:FD 50 (that is, forward 50)RT 90 (turn right 90 degrees)FD 50RT 90FD 50RT 90FD 50RT 90Here, the student programmer can easily visualize walkingand turning until he or she arrives back at the startingpoint. In keeping with Piaget’s theories, the learning is congruentwith the physical world and daily activities.Logo includes control structures similar to those inother languages, so the above program can be rewritten assimply:REPEAT 4 [FD 50 RT 90]Logo is much more than a set of simple drawing commands,however. Students can also be encouraged to use thelist-processing commands to create everything from computer-generatedpoetry to adventure games. Unlike LISP’sobscurely named commands such as car and cdr, Logo’s listcommands are readily understandable. For example, firstreturns the first item in a list, while butfirst returns all ofthe list except the first item.Logo procedures are introduced by the to keyword,implying that the programmer is “teaching the computer”how to do something. For example, a procedure to draw asquare with a variable size and starting position might looklike this: