+1 vote

Amdahl’s Law pertains to the speedup achieved when running a program on parallel processors versus using a single serial processor. In this context, speedup is the ratio of original running time to improved running time. According to Amdahl's Law, approximately how much speedup could we expect for an unlimited number of processors if 10 percent of a program is sequential( i.e. will not benefit from additional processors), and the remaining part is ideally parallel?

(A) 10X

(B) 20X

(C) 40X

(D) Infinite asked May 25
reshown May 27

Say the program takes 100 units time when executed sequentially .

Now, on the parallel processros, 10 % of the program is executed sequentially so time needed for that is 10 units.

Remaining 90 % of the program is run parrallely using unlimited no of processors  ,then  execution time is negligible.

So speed up = 100 unit /10 unit

=10

Speed up is approximately 10 times. answered May 29 by (1,650 points)
selected May 29

Let us consider that we have  x instructions:

Unmodified version:
Time taken is 1ns for each x instruction so total =xns.

Modified version:
10% are sequential,
let us consider each instruction takes 1ns then,
(0.1x) instructions each takes 1ns so->(0.1x)ns
and, remaining all the instructions can be executed parallely in 1ns
So, total time =(0.1x+1)ns

Speed up=x/(0.1x+1) =10. answered Jun 6 by (990 points)