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GATE 2015 CS (CS3) – Question 48

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

A pipeline reservation table uses S1 at times 1 and 5, S2 at times 2 and 4, and S3 at time 3. Find its minimum average initiation latency.

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Correct answer: 3

Explanation

Differences of occupied times in the same stage give forbidden latencies two and four. Starting jobs every three cycles gives differences three,six,nine,…, none forbidden, so average three is attainable. A gap one forces the next gap to be at least five because successive-start differences two and four would collide; such combinations cannot average below three. Therefore MAL=3.

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