Processor A has a CPI 1.2 and a clock rate of 1 GHz. Processor B has a CPI of 2.

Question

Processor A has a CPI 1.2 and a clock rate of 1 GHz. Processor B has a CPI of 2.0 and a clock rate of 2 GHz. Processor C has a clock rate of 2.5 GHz (400 ps/cycle) and a CPI of 2.6. All three processors implement the same instruction set. Determine the time per instruction for each processor and write it in the correct spot. Which processor is faster? How many times faster is it than the slowest processor? Show your work! Processor A time per instruction ______ Processor B time per instruction ______ Processor C time per instruction ______ Which is fastest? How many times faster than the slowest?

Explanation / Answer

It is given that all the three Processors implement the same instruction set.

Thus, time per instruction of each processor can be given by the formula:

Instructions per second = Clock Rate / CPI

Thus

For Processor A:

Instruction per second = 1 / 1.2 = 0.8 x 109instructions per second

Time per instructions = 1 / Instructions per time = 1 / (0.8 x 109) = 1.19 x 10-9 seconds per instructions

For Processor B:

instructions per second = 2 / 2 = 1.0 x 109instructions per second

Time per instruction = 1 / instructions per second = 1.0 x 10-9 seconds per instructions

For Processor C:

instructions per second = 2.5 / 2.6 = 0.96 x 109instructions per second

Time per instruction = 1 / instructions per second = 1.04 x 10-9 seconds per instructions

The processor which takes the least time to execute one instruction would be called the fastest.

According to all the data we have calculated above, Processor B is the fastest processor. And Processor A is the slowest processor.

Now Processor A : Processor B = IPS(B) / IPS (A)

= 1.0 / 0.8 = 1.25

Thus, Processor B is 1.25 times faster than processor A.

Hope this helps...

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