amdahl's law
 

* 1.(Computers) law which states that there is a limit to additional speed gained by using multiple parallel processors because some portions of programs must be executed serially* &lt parallel&gt (Named after Gene Amdahl) 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).