Project ForgeProcesses 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?
- A22
- B15
- C37
- 19
Explanation
Trace: P1 runs [0-1] (remaining 9) then P2 arrives (13, more, continue P1) [1-2] (remaining 8), then P3 arrives (6, shortest, preempt) — P3 runs [2-8] (completes, no shorter arrivals before P4 arrives exactly at t=8). At t=8: remaining are P1(8), P2(13), P4(9, just arrived) — P1 shortest, runs [8-16] (completes). Then P4(9) vs P2(13): P4 runs [16-25] (completes). Finally P2 runs [25-38] (completes). Turnaround = completion−arrival: P1=16, P2=37, P3=6, P4=17. Average = (16+37+6+17)/4 = 76/4 = 19.
Source: GATE CS 2025 (Session 2 / CS2) (2025)
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