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Instruction Pipelining

GATE CSE 2023 · Q33

NAT1 markEasy

Time

Consider a 3-stage pipelined processor having a delay of 10 ns (nanoseconds), 20 ns, and 14 ns, for the first, second, and the third stages, respectively. Assume that there is no other delay and the processor does not suffer from any pipeline hazards. Also assume that one instruction is fetched every cycle. The total execution time for executing 100 instructions on this processor is ___________ ns.

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Solution

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Official answer: 2040

Instruction Pipelining

To find the total execution time of a pipelined processor:

  1. Determine the clock cycle time (TclockT_{\text{clock}}): The clock cycle is determined by the maximum stage delay among all stages plus any intermediate buffer/latch delay (which is 00 here).

    Tclock=max⁡(10 ns,20 ns,14 ns)=20 nsT_{\text{clock}} = \max(10\text{ ns}, 20\text{ ns}, 14\text{ ns}) = 20\text{ ns}
  2. Determine the total number of cycles required: For a kk-stage pipeline executing nn instructions with no pipeline hazards:

    Total Cycles=k+(n−1)\text{Total Cycles} = k + (n - 1)

    Given k=3k = 3 stages and n=100n = 100 instructions:

    Total Cycles=3+(100−1)=102 cycles\text{Total Cycles} = 3 + (100 - 1) = 102\text{ cycles}
  3. Calculate total execution time:

    Execution Time=102×20 ns=2040 ns\text{Execution Time} = 102 \times 20\text{ ns} = 2040\text{ ns}

Thus, the total execution time is 2040 ns.

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This Instruction Pipelining previous year question is Q33 of the GATE CSE 2023 paper. Find more GATE CSE PYQs on Instruction Pipelining in Computer Organization and Architecture, or browse all GATE CSE PYQs.

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Instruction Pipelining in GATE CSE

Instruction Pipelining has 25 GATE CSE PYQs across 20 papers from 2011 to 2026. This is the only 1-mark NAT question among them, and it is the only one in GATE CSE 2023.

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GateAI solution cardGATE CSE 2023 · Q33 · NAT

Consider a 3-stage pipelined processor having a delay of 10 ns (nanoseconds), 20 ns, and 14 ns, for the first, second, and the third stages, respectively. Assume that there is no other delay and the processor does not suffer from any pipeline hazards. Also assume that one instruction is fetched every cycle. The total execution time for executing 100 instructions on this processor is … ns.

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Independent practice explanation verified by the GateAI team. GATE is conducted by the IITs; question text follows the official paper.