In an FCFS scheduling system, if multiple short CPU-bound processes arrive immediately after a single long CPU-bound process, what is the primary impact on the average waiting time of the short processes?
medium🧾🤔 Trace Reasoning Q4 of Q15
Operating Systems - FCFS Scheduling - Convoy Effect & Waiting Time
In an FCFS scheduling system, if multiple short CPU-bound processes arrive immediately after a single long CPU-bound process, what is the primary impact on the average waiting time of the short processes?
AThe short processes experience increased waiting times due to the long process blocking the queue.
BThe short processes have reduced waiting times because they are scheduled immediately after the long process.
CThe waiting times for short processes remain unaffected as FCFS treats all processes equally.
DThe short processes are executed in parallel, so waiting time is minimized.
Step-by-Step Solution
Solution:
Step 1: Identify the scheduling order
FCFS schedules processes in the order they arrive, so the long CPU-bound process runs first.
Step 2: Analyze waiting time for short processes
Short processes must wait until the long process finishes, increasing their waiting time significantly.
Final Answer:
Option A -> Option A
Quick Check:
Long process first causes delay for short ones [OK]
Quick Trick:Long first process delays all subsequent short processes [OK]
Common Mistakes:
MISTAKES
Assuming short processes run immediately after arrival
Believing FCFS reduces waiting time for short processes
Thinking processes execute in parallel under FCFS
Trap Explanation:
PITFALL
Option B looks plausible because short processes arrive after the long one but ignores FCFS ordering.
Interviewer Note:
CONTEXT
Tests understanding of how FCFS scheduling impacts waiting times and convoy effect.
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