Remember, the value of α is between 0 and 1. Now, let us put some values of α and compute the speed up factor for increasing values of number of processors. We get that the S(N) keeps on decreasing with increase in the value of α (i.e. number of sequential operations as shown in Figure).
No. of processors required
Figure:- Speed-up vs. Number of Processors
The graph in Figure clearly shows that there is a bottleneck caused due to sequential operations in a parallel computer. Even when the amount of sequential operations is more, after increasing the number of processors, the speed up factor S (N) degrades.
The sequential fraction i.e. α can be compared with speed up factor S(N) for a fixed value of N say 500. Figure shows a pictorial view of effect of Amdahl's law on the speed up factor.
α (Sequential Operations)