What happens to the waiting times of the short processes?
easy🧠🧾 Concept Trace Q12 of Q15
Operating Systems - FCFS Scheduling - Convoy Effect & Waiting Time
Trace the waiting time behavior step-by-step when a long CPU-bound process arrives first, followed by several short processes in FCFS scheduling. What happens to the waiting times of the short processes?
AShort processes start immediately after arrival, so their waiting times are minimal
BShort processes wait for the long process to finish, causing their waiting times to increase significantly
CShort processes preempt the long process to reduce their waiting times
DWaiting times of short processes remain unaffected because FCFS schedules based on burst time
Step-by-Step Solution
Step 1: Understand FCFS scheduling order
Processes are scheduled strictly in arrival order without preemption.
Step 2: Analyze the scenario
The long CPU-bound process arrives first and runs to completion. Short processes arriving later must wait until the long process finishes.
Step 3: Impact on waiting times
Short processes experience increased waiting times because they cannot start until the long process completes.
Step 4: Evaluate options
A is incorrect because short processes do not start immediately. B is correct as it describes the convoy effect where short processes wait behind a long one. C is incorrect because FCFS is non-preemptive. D is incorrect because FCFS does not schedule based on burst time.
Final Answer:
Option B -> Option B
Quick Check:
Convoy effect causes short processes to wait behind long ones in FCFS.
Quick Trick:In FCFS, long first -> short wait longer (convoy effect)
Common Mistakes:
MISTAKES
Assuming short processes can preempt long ones
Believing waiting times depend on burst time in FCFS
Thinking short processes start immediately after arrival
Trap Explanation:
PITFALL
Option A is tempting because short processes arrive and might seem ready to run, but FCFS queues strictly by arrival. Option C is a common misconception about preemption. Option D confuses FCFS with shortest-job-first scheduling.
Interviewer Note:
CONTEXT
Tests understanding of the convoy effect and waiting time accumulation in FCFS.
Master "FCFS Scheduling - Convoy Effect & Waiting Time" in Operating Systems
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