A rule first formalised by Gene Amdahl in 1967, which states that if F is the fraction of a calculation that is serial and 1-F the fraction that can be parallelized, then the speedup that can be achieved using P processors is: 1/( F + (1-F)/P) which has a limiting value of 1/F for an infinite number of processors. This no matter how many processors are employed, if a calculation has a 10% serial component, the maximum speedup obtainable is 10.