Operating Systems - Shortest Job First (SJF) - Preemptive vs Non-Preemptive
In which scenario is preemptive Shortest Job First (SJF) scheduling preferred over non-preemptive SJF?
In which scenario is preemptive Shortest Job First (SJF) scheduling preferred over non-preemptive SJF?
easy🔍 Pattern Recognition Q11 of Q15
Step-by-Step Solution
Step 1: Understand preemptive SJF behavior
Preemptive SJF allows the CPU to switch to a newly arrived process if it has a shorter burst time than the currently running process.Step 2: Analyze scenarios
If new processes with shorter burst times can arrive anytime, preemptive SJF ensures the CPU always runs the shortest job next, improving average waiting time.Step 3: Why other options are incorrect
A: If all processes arrive simultaneously with similar burst times, preemptive advantage is minimal.
B: Starvation is a concern in preemptive SJF, so it's not chosen when fairness is ignored.
C: Preemptive SJF increases context switches, so it's not preferred when minimizing overhead.Final Answer:
Option A -> Option AQuick Check:
Preemptive SJF is best when shorter jobs can arrive anytime, requiring immediate preemption.
Quick Trick: Preemptive SJF shines when shorter jobs arrive unpredictably [OK]
Common Mistakes:
MISTAKES- Assuming preemptive SJF always reduces overhead
- Believing preemptive SJF is best when all jobs arrive simultaneously
Trap Explanation:
PITFALL- Options A and C seem plausible because they mention common scheduling concerns, but they ignore the key advantage of preemption in handling dynamic arrivals.
Interviewer Note:
CONTEXT- Tests candidate's ability to identify when preemptive SJF is beneficial versus non-preemptive.
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