Amdahl's law is a widely used law that is used to design processors and parallel algorithms. It states that the maximum speedup that can be achieved is limited by the serial component of the program:
1 – P denotes the serial component (not parallelized) of a program.
This means that, for example, if a program in which 90% of the code can be made parallel, but 10% must remain serial, then the maximum achievable speedup is 9, even for an infinite number of processors.