GATE Overflow | Mock GATE | Test 1 | Question: 60

Question

A program runs in $20s$ in machine A  with a clock speed of $200MHz$. A computer architecture wants to build a machine B which will run this program in $6$ seconds. The architect has delivered that a substantial increase in clock rate is possible, but this will affect the design of rest of the CPU causing machine B to require $1.2$ times as many as clock cycles as machine A for this program. What clock rate should be targeted for  a best design? (In $MHz$)

Comments

Yes, I think an answer might be wrong...

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A small misprint in the question. Its 20s and not 20ms. 20ms doesn't make sense. 20s reduced to 6s makes sense. Thanks for pointing it out.

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ok...

Answer 1

Machine A, Cycle Time $= \frac{1}{200MHZ} = 5ns$

number of cyles needed = total time taken / Cyle time

$=\frac{20 Seconds}{5ns} = 4*10^9$

Machine B, cyles needed $= 1.2*4*10^9 = 4.8*10^9$

Total time taken = 6 seconds

Cycle Time = Total Time Taken/ Number of Cycles Needed

$=\frac{6 Seconds}{4.8*10^9} = 1.25ns$

Frequnecy $= \frac{1}{1.25ns} = 800 MHZ$

Answer 2

1 sec 200*${10^{6}}$ cycles

20 sec 20x200*${10^{6}}$ cycles

6 sec total cycles  1.2*20*200*10^6cycles

1 sec total cycle is (1.2*20*200*10^6)/6 =800*10^6

so 800 MHZ