Which CPU-scheduling algorithm is inherently pre-emptive because it allocates…
2010
Which CPU-scheduling algorithm is inherently pre-emptive because it allocates each ready process a fixed time quantum?
Answer: A. Round Robin (RR) — ConceptPre-emptive scheduling allows the operating system to interrupt a running process and reassign the CPU before that process finishes. An algorithm is…
- A.
Round Robin (RR)
- B.
First-Come, First-Served (FCFS)
- C.
Shortest Job First (SJF)
- D.
Priority scheduling
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Show answer & explanation
Correct answer: A
Concept
Pre-emptive scheduling allows the operating system to interrupt a running process and reassign the CPU before that process finishes.
An algorithm is inherently time-sliced when every ready process receives a bounded quantum and quantum expiry triggers pre-emption.
Application
Round Robin (RR) applies this rule through a circular ready queue.
Suppose the ready queue contains P1 followed by P2 and the time quantum is 4 ms.
Run P1 for at most 4 ms. If P1 is still unfinished when the quantum expires, the scheduler pre-empts it.
Place the unfinished P1 at the rear of the ready queue, then give P2 the next quantum.
Repeat the rotation. Queue removal and reinsertion are O(1) with a deque, while the quantum length controls response time and context-switch overhead.
Cross-check
Contrast the scheduling rules:
First-Come, First-Served normally runs the current process until it blocks or completes.
Shortest Job First is non-pre-emptive in its basic form; its pre-emptive counterpart is Shortest Remaining Time First.
Priority scheduling may be either pre-emptive or non-pre-emptive, so its name alone does not imply a fixed quantum.
Therefore, the uniquely time-quantum-driven pre-emptive choice is Round Robin (RR).