We wish to compare two systems S1 and S2. The table below presents measurements

Question

We wish to compare two systems S1 and S2. The table below presents measurements for the two systems when running two programs, Program 1 and Program 2. System 1 System 2 Program ExT (sec) IC ExT (sec) IC 1 12x106 8 10x10 10 1. If the clock rate of system S1 is 4 MHz and the clock rate for system S2 is 6 MHz, find CPI For each system when running Program 1 CPI for S1 CPI for S2 2. Assuming the CPI for each system when running Program 2 is the same as it is when running Program 1, find the instruction count (IC) for each system when running Program 2 for S1 IC for S2

Explanation / Answer

Solution:

• CPU has a fixed clock cycle time C = 1/clock rate sec/cycle

C1=1/4*10^6=2.5*10^-7 s

C2=1/6*10^6=1.6*10^-7s

T = I x CPI x C

T=execution Time per program in seconds

I= Number of instructions executed

CPI=average CPI for program

C=CPU Clock cycle

CPI=T/(I*C)

For system 1,

CPI(cycles per instruction)= 6/(12*10^6 * 2.5*10^-7)=2

For system 2,

CPI(cycles per instruction)= 8/(10*10^6 * 1.6*10^-7)=5

2. Assuming the CPI for each system when running Program 2 is the same as it is when running Program 1, find the instruction count (IC) for each system when running Program 2 for S1 IC for S2

For Program 2,

For System 1

CPI=2

IC=?

T=10

T = I x CPI x C

I=T/CPI*C

I =10/2*2.5*10^-7= 20000000=20*10^6

For System 2

CPI=5

IC=?

T=6

T = I x CPI x C

I=T/CPI*C

I =6/5*1.6*10^-7=7500000=7.5*10^6

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