GATE | GATE-CS-2000 | Question 8

Comparing the time T1 taken for a single instruction on a pipelined CPU with time T2 taken on a non­ pipelined but identical CPU, we can say that
(A) T1 <= T2 (B) T1 >= T2

(C) T1 < T2 (D) T1 is T2 plus the time taken for one instruction fetch cycle


Answer: (B)

Explanation: Pipelining does not increase the execution time of a single instruction. It increases the overall performance by executing instructions in multiple pipeline stages.

We assume that each stage takes ‘T’ unit of time both in pipelined and non-pipelined CPU.
Let total stages in pipelined CPU = Total stages in non-pipelined CPU = K and number of Instructions = N = 1

• Pipelined CPU : Total time (T1) = (K + (N – 1)) * T = KT
• Non-Pipelined CPU : Total time (T2) = KNT = KT

  Considering buffer delays in pipelined CPU, T1 >= T2

   Thus, option (B) is the answer.

  Please comment below if you find anything wrong in the above post.

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