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Instruction Pipelining

GATE CSE 2025 Set 2 · Q56

NAT2 marksMedium

Time

A 5-stage instruction pipeline has stage delays of 180, 250, 150, 170, and 250, respectively, in nanoseconds. The delay of an inter-stage latch is 10 nanoseconds. Assume that there are no pipeline stalls due to branches and other hazards. The time taken to process 1000 instructions in microseconds is _________ . (rounded off to two decimal places)

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Official answer: 261.04 (±0.84) (±0.84)

Instruction Pipelining
  1. Determine the clock cycle time (tclockt_{\text{clock}}): The stage delays are 180,250,150,170,180, 250, 150, 170, and 250 ns250\text{ ns}.

    Maximum stage delay=max⁡(180,250,150,170,250)=250 ns\text{Maximum stage delay} = \max(180, 250, 150, 170, 250) = 250\text{ ns}
    Latch delay=10 ns\text{Latch delay} = 10\text{ ns}
    tclock=250+10=260 ns=0.26 μst_{\text{clock}} = 250 + 10 = 260\text{ ns} = 0.26\,\mu\text{s}
  2. Determine the total number of clock cycles: For a kk-stage pipeline executing nn instructions with no stalls:

    k=5,n=1000k = 5, \quad n = 1000
    Total cycles=k+(n−1)=5+999=1004 cycles\text{Total cycles} = k + (n - 1) = 5 + 999 = 1004\text{ cycles}
  3. Calculate total execution time:

    T=1004×260 ns=261040 ns=261.04 μsT = 1004 \times 260\text{ ns} = 261040\text{ ns} = 261.04\,\mu\text{s}

Thus, the time taken is 261.04 microseconds (acceptable range: 260.20 to 261.20).

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This Instruction Pipelining previous year question is Q56 of the GATE CSE 2025 Set 2 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. 16 of them are 2-mark NAT questions like this one, and it is the only one in GATE CSE 2025 Set 2.

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A 5-stage instruction pipeline has stage delays of 180, 250, 150, 170, and 250, respectively, in nanoseconds. The delay of an inter-stage latch is 10 nanoseconds. Assume that there are no pipeline stalls due to branches and other hazards. The time taken to process 1000 instructions in microseconds is … (rounded off to two decimal places)

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