Question

Ben builds a 1 GHz processor where two important programs, A and B, take one second each to execute. Each program has a CPI of 2. Elaine is tasked with designing the company's next-generation processor. She comes up with an idea that improves the CPI of A to 1.5 and the CPI of B to 1.8. But the idea is so complex that the processor can only be implemented with a cycle time of 1.2 ns. Does Elaine's new processor out-perform Ben's processor on program A? How about on program B?

Answer 1

`Hey,

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Performance = clock speed / CPI instructions per second
1Ghz processor:
PerformanceA = clock rate / CPI A = (1 * 10^9)/(2) = 2*10^9 instructions per second
PerformanceB = clock rate / CPI B =(1 * 10^9)/(2) = 2*10^9 instructions per second

New processor:
new CPIA =1.5
new CPIB = 1.8
new clock rate = 1/(1.2 * 10^(9))
= 0.83 * 10^9 Hz = 0.83GHZ
new Performance A = new clock rate / new CPIA = (0.83 * 10^9)/1.5
= 0.55 *10^9 instructions per second
new Performance B = new clock rat / new CPIB = (0.83 * 10^(9))/1.8
= 0.46 * 10^9 instructions per second
=> Program A has better performance than program B with the new processor

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Thanks.