Consider a processor executing a program consisting of 3 different instructions

Question

Consider a processor executing a program consisting of 3 different instructions classes (A, B, C), each with the same CPI, and with distributions A=40%, B=40%, C=20%. As currently implemented, the program executes in 500 milliseconds.

a) How long would it take for the program to fully execute if we modify the processor such that the speed of class B instructions is doubled (i.e., class B instructions take half as long after the improvement)?

b) In this scenario, how much faster is the improved processor relative to the original?

Explanation / Answer

1. Currently B takes 40% time of 500 ms. That would mean 200ms. If the speed of class B instructions is doubled, then B would take 100 ms to execute, therefore the program would execute for 400ms.

2. In this scenario CPU is 20% faster than before as earlier when it took 500ms now it takes 400ms so an improvement of 20% of speed.

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