Operating Systems - Shortest Job First (SJF) - Preemptive vs Non-Preemptive
Consider three processes arriving at time 0 with burst times 6, 8, and 7 units respectively. Under preemptive SJF, which process will be running at time 5?
Consider three processes arriving at time 0 with burst times 6, 8, and 7 units respectively. Under preemptive SJF, which process will be running at time 5?
easy🧠🧾 Concept Trace Q3 of Q15
Step-by-Step Solution
Solution:
Step 1: Trace process execution under preemptive SJF
All processes arrive at time 0: burst times 6, 8, and 7.Step 2: Execution timeline
Process with burst 6 runs first from 0 to 6 (shortest remaining time).Step 3: Determine process running at time 5
At time 5, process with burst 6 is still running (not completed yet).Final Answer:
Option C -> Option CQuick Check:
Process with burst 6 runs uninterrupted until completion [OK]
Quick Trick: No arrivals to preempt, shortest job runs [OK]
Common Mistakes:
MISTAKES- Assuming process with burst 7 or 8 runs at time 5
- Thinking CPU is idle without reason
- Confusing preemptive with non-preemptive behavior
Trap Explanation:
PITFALL- Candidates often forget that no new shorter jobs arrive to preempt the running process.
Interviewer Note:
CONTEXT- Tests understanding of preemptive SJF behavior with simultaneous arrivals.
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