Encyclopedia of Computer Science and Technology

86 chipsetattached to the silicon substrate, are formed by altering thesubstrate itself with tiny amounts of impurities (a processcalled “doping”). This creates regions with an excess ofelectrons (n-type, for negative) or a deficit (p-type for positive).The junction between a p and an n region functionsas a diode. More complex arrangements of p and n regionsform transistors. Layers of transistors and other devices canbe formed on top of one another, resulting in a highly compactintegrated circuit. Today this is generally done usingoptical lithography techniques, although as the separationbetween components approaches 100 nm (nanometers, orbillionths of a meter) it becomes limited by the wavelengthof the light used.In computers, the IC chip is used for two primary functions:logic (the processor) and memory. The microprocessorsof the 1970s were measured in thousands of transistorequivalents, while chips such as the Pentium and Athlonbeing marketed by the late 1990s are measured in tensof millions of transistors (see microprocessor). Meanwhile,memory chips have increased in capacity from the4K and 16K common around 1980 to 256 MB and more.In what became known as “Moore’s law,” Gordon Moorehas observed that the number of transistors per chip hasdoubled roughly every 18 months.Future TechnologiesAlthough Moore’s law has proven to be surprisingly resilient,new technologies will be required to maintain thepace of progress.In January 2007, Intel and IBM separately announced aprocess for making transistors out of the exotic metal hafnium.It turns out that hafnium is much better than the traditionalsilicon at preventing power leakage (and resultinginefficiency) through layers that are only about five atomsthick. Hafnium transistors can also be packed more closelytogether and/or run at a higher speed.Another approach is to find new ways to connect thetransistors so they can be placed closer together, allowingsignals to travel more quickly and thus provide fasteroperation. Hewlett-Packard (HP) is developing a way toplace the connections on layers above the transistors themselves,thus reducing the space between components. Thescheme uses two layers of conducting material separated bya layer of insulating material that can be made to conductby having a current applied to it. Although promising, theapproach faces difficulties in making the wires (only about100 atoms thick) reliable enough for applications such ascomputer memory or microprocessors.Ultimately, direct fabrication at the atomic level (seenanotechnology) will allow for the maximum densityand efficiency of computer chips.Further ReadingBaker, R. Jacob, Harry W. Li, and David E. Boyce. CMOS CircuitDesign, Layout and Simulation. New York: IEEE Press, 1998.Saint, Christopher and Judy Saint. IC Layout Basics. New York:McGraw-Hill, 2001.Semiconductor Industry Association. Available online. URL:http://www.sia-online.org/home.cfm. Accessed August 13,2007.Thompson, J. M. T., ed. Visions of the Future: Physics and Electronics.New York: Cambridge University Press, 2001.chipsetIn personal computers a chipset is a group of integratedcircuits that together perform a particular function. Systempurchasers generally think in terms of the processor itself(such as a Pentium III, Pentium IV, or competitive chipsfrom AMD or Cyrix). However they are really buying asystem chipset that includes the microprocessor itself (seemicroprocessor) and often a memory cache (which may bepart of the microprocessor or a separate chip—see cache)as well as the chips that control the memory bus (whichconnects the processor to the main memory on the motherboard—seebus.) The overall performance of the systemdepends not just on the processor’s architecture (includingdata width, instruction set, and use of instruction pipelines)but also on the type and size of the cache memory,the memory bus (RDRAM or “Rambus” and SDRAM) andthe speed with which the processor can move data to andfrom memory.In addition to the system chipset, other chipsets on themotherboard are used to support functions such as graphics(the AGP, or Advanced Graphics Port, for example), driveconnection (EIDE controller), communication with externaldevices (see parallel port, serial port, and USB), andconnections to expansion cards (the PCI bus).At the end of the 1990s, the PC marketplace had chipsetsbased on two competing architectures. Intel, whichoriginally developed an architecture called Socket 7, hasswitched to the more complex Slot-1 architecture, whichis most effective for multiprocessor operation but offersthe advantage of including a separate bus for accessing thecache memory. Meanwhile, Intel’s main competitor, AMD,has enhanced the Socket 7 into “Super Socket 7” and isoffering faster bus speeds. On the horizon may be completelynew architecture. In choosing a system, consumersare locked into their choice because the microprocessor pinsockets used for each chipset architecture are different.Further ReadingIntel. “Desktop Chipsets.” Available online. URL: http://www.intel.com/products/desktop/chipsets/. Accessed June 6, 2007.“Motherboards.” Available online. URL: http://www.motherboards.org/index.html. Accessed June 6, 2007.Walrath, Josh. “Chipsets Today and Tomorrow.” ExtremeTech.Available online. URL: http://www.extremetech.com/article2/0,1697,1845493,00.asp. Accessed June 6, 2007.Church, Alonzo(1903–1995)AmericanMathematicianBorn in Washington, D.C., mathematician and logicianAlonzo Church made seminal contributions to the fundamentaltheory of computation. Church was mentored bynoted geometer Oswald Veblen and graduated from Prince-