GATE | GATE-CS-2014-(Set-3) | Question 65

Consider the following processors (ns stands for nanoseconds). Assume that the pipeline registers have zero latency.

P1: Four-stage pipeline with stage 
    latencies 1 ns, 2 ns, 2 ns, 1 ns.
P2: Four-stage pipeline with stage 
    latencies 1 ns, 1.5 ns, 1.5 ns, 1.5 ns.
P3: Five-stage pipeline with stage 
    latencies 0.5 ns, 1 ns, 1 ns, 0.6 ns, 1 ns.
P4: Five-stage pipeline with stage 
    latencies 0.5 ns, 0.5 ns, 1 ns, 1 ns, 1.1 ns. 

Which processor has the highest peak clock frequency?

(A) P1
(B) P2
(C) P3
(D) P4


Answer: (C)

Explanation:



Peak clock frequency = 1 / Maximum latency

Maximum of latencies is minimum in P3

i.e. 

P1 : f= 1/2 = 0.5 GHz

P2: f=1/1.5 = 0.67 GHz

P4: f=1/1.1 GHz

P3 : f=1/1 GHz =1

Thus P3 is be the right answer

This explanation has been contributed by Abhishek Kumar.

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