In computer architecture, Amdahl's law (or Amdahl's argument) is a formula that shows how much faster a task can be completed when more resources are added to the system.

The law can be stated as:

"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".

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.

Amdahl's law is often used in parallel computing to predict the theoretical speedup when using multiple processors.

In the context of Amdahl's law, speedup can be defined as:

${\displaystyle {\text{Speedup}}={\frac {\text{Performance for the entire task when enhancements are applied}}{\text{Performance for the same task without those enhancements}}}}$

or