Question

Consider the following statements about CPU scheduling :
A. First come, first serve can lead to the “convoy effect”

B. Shortest job first minimizes average waiting time

C. Round robin does not use time quantum for fairness

D. Priority scheduling may cause starvation

E. Multilevel feedback queue combines preemptive and non preemptive scheduling

Choose the correct answer from the options given below :

• A. A, B, C, E only
• B. B, C, D, E only
• C. A, B, D, E only
• D. A, C, D only

Hint:

If you see "Round Robin" and "No Time Quantum" in the same sentence, it's a trap! Round Robin is simply FCFS with a timer.

Answer 1

The Correct Option is C

Concept:
• CPU scheduling algorithms determine which process in the ready queue is allocated to the CPU.
• Each algorithm has specific pros (like fairness or low wait time) and cons (like starvation or the convoy effect).

Step 1: Evaluate FCFS and SJF (A and B)

• Convoy Effect: In FCFS, if a long CPU-bound process starts first, all short I/O-bound processes wait behind it. Statement A is correct.
• Optimality of SJF: SJF is provably optimal for minimizing the average waiting time for a given set of processes. Statement B is correct.

Step 2: Evaluate Round Robin and Priority (C and D)

• Round Robin: This algorithm relies entirely on a "time quantum" to ensure no process hogs the CPU. Statement C is incorrect.
• Starvation: In Priority scheduling, a low-priority process may never run if high-priority processes are constantly added to the queue. Statement D is correct.

Step 3: Evaluate Multilevel Feedback Queue (E)
MLFQ uses multiple queues with different priorities and different scheduling algorithms (some might be preemptive like RR, some non-preemptive). It moves processes between queues based on behavior. Statement E is correct.