The primary limitation of the first come, first served (FCFS) priority rule is that short jobs will tend to delay longer jobs that follow. True False
The correct answer and explanation is :
Correct Answer: False
Explanation:
The primary limitation of the First Come, First Served (FCFS) scheduling rule is actually the opposite of what the statement claims. In an FCFS system, long jobs tend to delay shorter jobs rather than the other way around. This is due to the convoy effect, where shorter jobs must wait for long-running jobs to complete before they can be processed.
Understanding FCFS Scheduling:
FCFS is a non-preemptive scheduling algorithm, meaning once a process starts execution, it runs until completion without being interrupted. The processes are scheduled in the order they arrive in the queue.
Limitation: Convoy Effect
- If a long job arrives first, it will occupy the CPU until completion.
- Shorter jobs that arrive afterward must wait, even if they could have completed quickly.
- This results in high waiting times for shorter jobs.
Example Scenario:
Assume three jobs arrive at the CPU in the following order:
- Job A: 10 seconds execution time
- Job B: 2 seconds execution time
- Job C: 1 second execution time
Since FCFS processes jobs in arrival order, Job A will run first for 10 seconds. During this time, Jobs B and C must wait, even though they could have finished quickly.
Better Alternative:
- Shortest Job Next (SJN) or Shortest Job First (SJF) can reduce waiting times by executing shorter jobs first.
- Round Robin (RR) ensures fairness by allocating time slices.
Thus, the correct answer is False—long jobs delay shorter jobs in FCFS, not the other way around.