The GATE Grind

GATE 2025 CS (CS2) – Question 26

Operating System · CPU and I/O Scheduling · 1 mark · Multiple choice

Processes $P1, P2, P3, P4$ 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?

  1. 22
  2. 15
  3. 37
  4. 19

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Correct answer: (D) 19

Explanation

Schedule: P1 runs 0-2, P3 runs 2-8, P1 runs 8-16, P4 runs 16-25, P2 runs 25-38. Turnaround times are 16, 37, 6 and 17, summing to 76. The average is 76/4 = 19.