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Amdahl's law
Formula in computer architecture / From Wikipedia, the free encyclopedia
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In computer architecture, Amdahl's law (or Amdahl's argument[1]) is a formula which gives the theoretical speedup in latency of the execution of a task at fixed workload that can be expected of a system whose resources are improved. It states that "the overall performance improvement gained by optimizing a single part of a system is limited by the fraction of time that the improved part is actually used".[2] It is named after computer scientist Gene Amdahl, and was presented at the American Federation of Information Processing Societies (AFIPS) Spring Joint Computer Conference in 1967.
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Amdahl's law is often used in parallel computing to predict the theoretical speedup when using multiple processors. For example, if a program needs 20 hours to complete using a single thread, and a one-hour portion of the program cannot be parallelized, then only the remaining 19 hours' (p = 0.95) execution time can be parallelized. Therefore, regardless of how many threads are devoted to a parallelized execution of this program, the minimum execution time is always more than 1 hour. Hence, the theoretical speedup is, at most, 20 times the single thread performance, .