Encyclopedia of Computer Science and Technology

374 Plug and PlayImpact of the LanguageBecause of its many practical features and its availability forthe popular IBM 360 mainframes, PL/I enjoyed considerablesuccess in the late 1960s and 1970s. The language waslater ported to most major platforms and operating systems.When personal computers came along, PL/I becameavailable for IBM’s OS/2 operating system as well as forMicrosoft’s DOS and Windows, although the language neverreally caught on in those environments.Computer scientists such as structured programmingguru Edsger Dijkstra decried PL/I’s lack of a clear, welldefinedstructure. In his Turing Award Lecture in 1972,Dijkstra opined that “I absolutely fail to see how we cankeep our growing programs firmly within our intellectualgrip when by its sheer baroqueness the programming language—ourbasic tool, mind you!—already escapes ourintellectual control.” (See Dijkstra, Edsger.)On a practical level the sheer number of features inthe language meant that truly mastering it was a lengthyprocess. A language like C, on the other hand, had a muchsimpler “core” to master even though it was less versatile.PL/I also tended to retain the mainframe associations fromits birth at IBM, while C grew up in the world of minicomputersand the UNIX community and proved more suitablefor PCs. Nevertheless, PL/I provided many examples thatlanguage designers could use in attempting to design betterimplementations.Further ReadingThe Essentials of PL/I Programming Language. Piscataway, N.J.:Research and Education Association, 1993.Hughes, Joan Kirby. PL/I Structured Programming. 3rd ed. NewYork: Wiley, 1986.“PL/I Frequently Asked Questions (FAQ).” Available online. URL:http://www.faqs.org/faqs/computer-lang/pli-faq/. AccessedAugust 17, 2007.“The PL/I Language.” Available online. URL: http://home.nycap.rr.com/pflass/pli.htm. Accessed February 9, 2008.Sebesta, Robert W. Concepts of Programming Languages. 8th ed.Boston: Pearson Addison-Wesley, 2007.Plug and PlayIn early MS-DOS systems installation of new hardware suchas a printer often had to be performed manually by copyingfiles (see device driver) to the hard drive from floppiesand then making specified settings to the system configurationfiles AUTOEXEC.BAT and CONFIG.SYS. These settingsoften involved unfamiliar concepts such as interrupts(IRQs) and DMA (direct memory access) channels.When Windows came along, device manufacturers generallyprovided an installation program that takes care ofcopying the files and making the necessary changes to thesystem registry. However, there was still the problem ofensuring that one had a driver compatible with the versionof the operating system in use, and users were sometimesasked to make choices for which they were not prepared(such as choosing which port to use).By the mid-1990s, Intel was promoting a standard for theautomated detection and configuration of devices. Knownas Plug and Play (PnP), this standard was incorporated inversions of Microsoft Windows starting with Windows 95(see Microsoft Windows). The required hardware supportsoon appeared on PC motherboards and expansion cards.With Plug and Play the user simply connects a printer,scanner, or other device to the PC. Windows detects thata device has been connected and queries it for its officialname and other information. If necessary, Windows canthen prompt the user for a disk containing the appropriatedriver or even search for a driver on a Web site.The concept of Plug and Play extends beyond the Windowsworld, however. In recent years there has been interestin developing a Universal Plug and Play (UPnP) protocolby which a variety of devices could automatically configurethemselves with any of a variety of different networks.This would be particularly helpful for home users who areincreasingly setting up small networks so they can sharebroadband Internet connections, as well as the growingnumber of users who want their desktop PC to work withhandheld (palm) computers and other devices. Microsoftsupports UPnP in versions of Windows starting with MEand XP.Further ReadingBigelow, Stephen J. The Plug & Play Book. New York: McGraw Hill,1999.Shanley, Tom. Plug and Play System Architecture. Reading, Mass.:Addison-Wesley, 1995.Universal Plug and Play Forum. Available online. URL: http://www.upnp.org/. Accessed August 17, 2007.plug-inA number of applications programs include the ability forthird-party developers to write small programs that extendthe main program’s functionality. For example, thousandsof “filters” (algorithms for transforming images) have beenwritten for Adobe Photoshop. These small programs arecalled plug-ins because they are designed to connect tothe main program and provide their service whenever it isdesired or required.Perhaps the most commonly encountered plug-ins arethose available for Web browsers such as Firefox, Netscape,or Internet Explorer. Plug-ins can enable the browser to displaynew types of files (such as multimedia). Many standardprograms for particular kinds of files are now providedboth as stand-alone applications and as browser plug-ins.Examples include Adobe (PDF document format), AppleQuickTime (graphics, video, and animation), RealPlayer(streaming video and audio), and Macromedia Flash (interactiveanimation and presentation). These and many otherplug-ins are offered free for the downloading, in order toincrease the number of potential users for the formats andthus the market for the development packages.One of the most useful plug-ins found in most browsersis one that allows the browser to run Java applets (see Java).In turn, Java is often used to write other plug-ins.Beyond such traditional workhorses, a number of innovativebrowser plug-ins have appeared, particularly for the