AMDAHL'S LAW

Domain	Definition
Computing	Amdahl's Law (Named after Gene Amdahl) If F is the fraction of a calucation that is sequential, and (1-F) is the fraction that can be parallelised, then the maximum speedup that can be achieved by using P processors is 1/(F+(1-F)/P). [Gene Amdahl, "Validity of the Single Processor Approach to Achieving Large-Scale Computing Capabilities", AFIPS Conference Proceedings, (30), pp. 483-485, 1967]. (2001-03-26). Source: The Free On-line Dictionary of Computing.
Source: compiled by the editor from various references; see credits.

Specialty Definition: Amdahl's law

Amdahl's law, named after computer architect Gene Amdahl, states that if F is the fraction of a calculation that is sequential, and (1-F) is the fraction that can be parallelised, then the maximum speedup that can be achieved by using P processors is 1 / (F + (1-F)/P). In the limit, as P tends to infinity, the maximum speedup tends to 1/F. In practice, price/performance ratio falls rapidly as P is increased once (1-F)/P is small compared to F.

As an example, if F is only 10%, the problem can be sped up by only a maximum of a factor of 10, no matter how large the value of P used. For this reason, parallel computing is only useful for either small numbers of processors, or problems with very low values of F: so-called embarrassingly parallel problems.

A great part of the craft of parallel programming consists of attempting to reduce F to the smallest possible value.

References:

Gene Amdahl, "Validity of the Single Processor Approach to Achieving Large-Scale Computing Capabilities", AFIPS Conference Proceedings, (30), pp. 483-485, 1967.

External links

Reevaluating Amdahl's Law

Anagrams: AMDAHL'S LAW

Scrabble® Enable2K-Verified Anagrams
	Words within the letters "'-a-a-a-d-h-l-l-m-s-w"
	-3 letters: wadmaals.
	-4 letters: halalas, hamadas, wadmaal, wadmals, wallahs.
	-5 letters: almahs, halala, halmas, hamada, hamals, llamas, salaam, wadmal, wallah, wallas.
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