The limit of parallel speedup is determined by Amdahl's Law, which states that the maximum speedup that can be achieved by parallelizing a program is limited by the portion of the program that cannot be parallelized.
According to Amdahl's Law, if a fraction p of a program is parallelizable and the remaining fraction (1-p) is sequential, then the maximum speedup that can be achieved by parallelizing the program is given by the formula:
Speedup = 1 / [(1-p) + (p/n)]
Where n is the number of processors used.
As the number of processors increases, the speedup approaches a maximum value determined by the sequential portion of the program. Therefore, the limit of parallel speedup is 1 / (1-p), where p is the portion of the program that can be parallelized.