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GATE 2014 CS (CS1) – Question 53

Computer Organization and Architecture · Instruction Pipelining and Pipeline Hazards · 2 marks · Numerical answer

A six-stage instruction pipeline has perfectly balanced stages and no cycle-time overhead. If 25% of instructions incur two pipeline stall cycles, find speedup relative to nonpipelined execution.

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Correct answer: 4 to 4

Explanation

Without pipelining each instruction takes6stage-times. The pipeline’s average CPI is1+0.25×2=1.5, because a quarter of instructions incur two extra cycles. Long-run speedup is6/1.5=**4**. Pipeline fill/drain overhead is neglected as intended.