Consider the following processors (ns stands for nanoseconds).

Home » Computer Organization and Architecture » Computer organization and architecture miscellaneous » Question

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 ?

1. P1
2. P2
3. P3
4. P4

Correct Option: C

Frequency ∝	1
	clock period

Clock period = maximum stage delay + overhead
P₁ : CP = Max (1, 2, 2, 1) = 2 ns
P₂ : CP = Max (1, 1.5, 1.5, 1.5) = 1.5 ns
P₃ : CP = Max (0.5, 1, 1, 0.6, 1) = 1 ns
P₄ : CP = Max (0.5, 0.5, 1, 1, 1, 1) = 1.1 ns
∵ CP of P₃ is less, it has highest frequency

Frequency 1 P₃ =	1	= 1 GHz
	1 ns