a) Assume a given computer x executes three different programs A, B& C in the sa

Question

a)     Assume a given computer x executes three different programs A, B& C in the same amount of time. Is MIPS be the same? If theanswer is yes, is MIPS always the same for a given computer for anyprogram?

b)     Assume two different computers X & Y executes the same program.X finishes in ½ the time of Y. What can you conclude aboutthe MIPS rate of the two different computers?

c)       Assume that a given computerX runs any given program in a certain amount of time. If computer Xis over clocked (i.e. the clock rate is increased) will it alwaysrun the same program in less time? If it is over clocked will MIPSgo up regardless of what program it is running?

Explanation / Answer

(a)

When a computer executes three instructions in the same amountof time, it doesn’t mean that the MIPS of the three programsis same. The execution time of the three programs may be same dueto various factors like instruction count, CPI, Clock cycle timeetc. MIPS vary between programs on the same computer. A computercannot have a single MIPS rating for all programs.

(b)

For given program, MIPS = Instruction Count/Exec Time * 106

Since the two computers are executing the same program, theinstruction count will be same, and let it be 10.

The execution time for the two computers vary, and given as Xfinishes in ½ the time of Y.

So, let the execution time for X is 5 and execution time for Yis 10.

MIPS of X = 10 / 5 x

                  = 2,000,000

MIPS of Y = 10 / 10 x

                  = 1,000,000

So we can conclude that the MIPS rate of X is larger than thatof Y and even if the same program is executed on two differentcomputers, the MIPS rate will not be same. It differs from computerto computer and program to program.

(c)

Since the execution time is the # clock cycles / clock rate, ifthe clock rate is increased, the program can be run in lesstime.

And also, the MIPS goes up because, MIPS depends on executiontime and if clock rate increases, the execution time decreases, andhence MIPS increases.

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