Central processing unit: Difference between revisions

Revision as of 13:12, 10 August 2011

Revision as of 17:48, 10 August 2011

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[[Image:Edvac.jpg|thumb|[[EDVAC]], one of the first stored program computers]]

ComputersKomputers 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.

The structure 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 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 design of a computer that would eventually be completed in August 1949.<ref>{{cite paper | author = [[]] | title = First Draft of a Report on the EDVAC | publisher = Pennsylvania School of Electrical Engineering, [[University of Pennsylvania]] | url = http://www.virtualtravelog.net/entries/2003-08-TheFirstDraft.pdf | date = 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.