Amdahl's Law

Last Updated: April 13, 2018

Definition - What does Amdahl's Law mean?

Amdahl’s law is a formula used to find the maximum improvement possible by improving a particular part of a system. In parallel computing, Amdahl's law is mainly used to predict the theoretical maximum speedup for program processing using multiple processors. It is named after Gene Amdahl, a computer architect from IBM and the Amdahl Corporation.

This term is also known as Amdahl’s argument.

Techopedia explains Amdahl's Law

Amdahl’s law states that in parallelization, if P is the proportion of a system or program that can be made parallel, and 1-P is the proportion that remains serial, then the maximum speedup that can be achieved using N number of processors is 1/((1-P)+(P/N).

If N tends to infinity then the maximum speedup tends to 1/(1-P).

Speedup is limited by the total time needed for the sequential (serial) part of the program. For 10 hours of computing, if we can parallelize 9 hours of computing and 1 hour cannot be parallelized, then our maximum speedup is limited to 10x.

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