Central processing unit: Difference between revisions

Revision as of 02:17, 21 August 2011

Revision as of 17:37, 26 August 2011

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Computers such as the [[ENIAC]] had to be physically rewired in order to perform different tasks, which caused these machines to be called "fixed-program computers." Since the term "CPU" is generally defined as a [[software]] (computer program) execution device, the earliest devices that could rightly be called CPUs came with the advent of the stored-program computer.

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The idea of a stored-program computer was already present in the design of [[J. Presper Eckert]] and [[John William Mauchly]]'s ENIAC, but was initially omitted so that it could be finished sooner. On June&nbsp;30, 1945, before ENIAC was made, mathematician [[John von Neumann]] distributed the paper entitled ''[[First Draft of a Report on the EDVAC]]''. It was the outline of a stored-program computer that would eventually be completed in August 1949.<ref>{{cite journal | author = | title = First Draft of a Report on the EDVAC | publisher = [[Moore School of Electrical Engineering]], [[University of Pennsylvania]] | url = http://www.virtualtravelog.net/entries/2003-08-TheFirstDraft.pdf | year = 1945 }}</ref> EDVAC was designed to perform a certain number of instructions (or operations) of various types. These instructions could be combined to create useful programs for the EDVAC to run. Significantly, the programs written for EDVAC were stored in high-speed [[Memory (computers)|computer memory]] rather than specified by the physical wiring of the computer. This overcame a severe limitation of ENIAC, which was the considerable time and effort required to reconfigure the computer to perform a new task. With von Neumann's design, the program, or software, that EDVAC ran could be changed simply by changing the contents of the memory.

Early CPUs were custom-designed as a part of a larger, sometimes one-of-a-kind, computer. However, this method of designing custom CPUs for a particular application has largely given way to the development of mass-produced processors that are made for many purposes. This standardization began in the era of discrete [[transistor]] [[Mainframe computer|mainframes]] and [[minicomputer]]s and has rapidly accelerated with the popularization of the [[integrated circuit]]&nbsp;(IC). The IC has allowed increasingly complex CPUs to be designed and manufactured to tolerances on the order of [[nanometer]]s. Both the miniaturization and standardization of CPUs have increased the presence of digital devices in modern life far beyond the limited application of dedicated computing machines. Modern microprocessors appear in everything from [[automobile]]s to [[cell phone]]s and children's toys.