If we want to use more than one node to speed up P, it will only affect P2 by a factor of s>1:

The speedup of the process P can be easily calculated as follows:

The ratio of the parallelizable portion of a process to its total is represented by b and is calculated as follows:

For example, in the preceding scenario, b = 8/10 = 0.8.

Simplifying these equations will give us Amdahl's law:

Here, we have the following:

• P is the overall process.
• b is the ratio of the parallelizable portion of P.
• s is the speedup achieved in the parallelizable portion of P.

Let's assume that we plan to run the process P on three parallel nodes:

• P1 is the sequential portion and cannot be reduced by using parallel nodes. It will remain at 2 seconds.
• P2 now takes 3 seconds instead of 9 seconds.

So, the total time taken by process P is reduced to 5 seconds, as shown in the following diagram:

In the preceding example, we can calculate the following:

• n_p = the number of processors = 3
• b = the parallel portion =  9/11 = 81.81%
• s = the speedup = 3

Now, let's look at a typical graph that explains Amdahl's law:

In the preceding diagram, we draw the graph between s and n_p for different values of b.