Encyclopedia of Computer Science and Technology

264 kernelcould send a message to the button program object, whichwould be programmed to respond in specific ways.After leaving Xerox PARC in 1983, Kay briefly servedas chief scientist at Atari and then moved to Apple, wherehe worked on Macintosh and other advanced projects. In1996, Kay became a Disney Fellow and Vice President ofResearch and Development at Walt Disney Imagineering.In 2001 Kay founded Viewpoints Research Institute, a nonprofitorganization devoted to developing advanced learningenvironments for children. One such project is Squeak,a streamlined but powerful version of Smalltalk that Kaystarted developing in 1995. Another, eToys, is a multiplatform,media-rich, environment that can be used for educationor “just” play. Behind it all is Kay’s continuing effortto do no less than reinvent programming and peoples’ relationshipto computer environments.Kay’s numerous honors include the ACM Turing Award(2003) for contributions to object-oriented programmingand the Kyoto Prize (2004).Further ReadingAlter, Allan E. “Alan Kay: The PC Must Be Revamped—Now.” CIOInsight. Available online. URL: http://www.cioinsight.com/article2/0,1540,2089567,00.asp. Accessed August 1, 2007.Gasch, Scott. “Alan Kay.” Available online. URL: http://ei.cs.vt.edu/~history/GASCH.KAY.HTML. Accessed August 12, 2007.Kay, Alan. “The Early History of Smalltalk.” In Thomas J. Bergin,Jr., and Richard G. Gibson, Jr., eds. History of ProgrammingLanguages II. New York: ACM; Reading, Mass.: Addison-Wesley,1996.Shasha, Dennis, and Cathy Lazere, eds. Out of their Minds: TheLives and Discoveries of 15 Great Computer Scientists. NewYork: Copernicus, 1995.Viewpoints Research Institute. Available online. URL: http://www.vpri.org/. Accessed August 12, 2007.kernelThe idea behind an operating system kernel is that thereis a relatively small core set of “primitive” functions thatare necessary for the operation of system services (see alsooperating system). These functions can be provided in asingle component that can be adapted and updated as desirable.The fundamental services include:• Process control—scheduling how the processes (programsor threads of execution within programs) sharethe CPU, switching execution between processes, creatingnew processes, and terminating existing ones(see multitasking).• Interprocess communication—sending “messages”between processes enabling them to share data orcoordinate their data processing.• memory management—allocating and freeing upmemory as requested by processes as well as implementingvirtual memory, where physical storage istreated as an extension of main (RAM) memory. (Seememory management.)The kernel is an intermediary between users and programs and thehardware system. It provides the functions necessary for allocatingand controlling processes and system resources.• File system services—creating, opening, reading from,writing to, closing, and deleting files. This includes maintaininga structure (such as a list of nodes) that specifiesthe relationship between directories and files. (See file.)In addition to these most basic services, some operatingsystems may have larger kernels that include securityfunctions (such as maintaining different classes of userswith different privileges), low-level support for peripheraldevices, and networking (such as TCP/IP).The decision about what functions to include in the kerneland which to provide through device drivers or systemextensions is an important part of the design of operatingsystems. Many early systems responded to the very limitedsupply of RAM by designing a “microkernel” that could fitentirely in a small amount of memory reserved permanentlyfor it. Today, with memory a relatively cheap resource, kernelstend to be larger and include functions that are pageddynamically into and out of memory.In the UNIX world (and particularly with Linux) thekernel is constantly being improved through informal collaborativeefforts. Many Linux enthusiasts regularly installnew versions of the kernel in order to stay on the “leadingedge,” while more conservative users can opt for waitinguntil the next stable version of the kernel is released.Further ReadingBovet, Daniel, and Marco Cesati. Understanding the Linux Kernel.3rd ed. Sebastapol, Calif.: O’Reilly, 2005.Love, Robert. Linux Kernel Development. 2nd ed. Indianapolis:Novell Press, 2005.Torvalds, Linus. “LinuxWorld: The Story of the Linux Kernel.”linuxtoday. Available online. URL: http://www.linuxtoday.com/developer/1999032500910PS. Accessed August 12, 2007.