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GATE CSE 2025 Session 2 Q26: Average turnaround time under SRTF scheduling

Question

Processes P1,P2,P3,P4P_1, P_2, P_3, P_4 arrive in that order at times 0, 1, 2, and 8 milliseconds respectively, and have execution times of 10, 13, 6, and 9 milliseconds respectively. Shortest Remaining Time First (SRTF) algorithm is used as the CPU scheduling policy. Ignore context switching times.

Which ONE of the following correctly gives the average turnaround time of the four processes in milliseconds?

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Answer: D (official GATE 2025 final answer key)

Concept used: Preemptive shortest-job scheduling: at each arrival, run the job with the least remaining time.

First step: At t=2t = 2, P3P_3 (6 ms) preempts P1P_1 (8 ms left); draw the Gantt chart from there.

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Source: official GATE 2025 Session 2 CS question paper and final answer key, organised by IIT Roorkee. Question paper · Answer key

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