Question

Which one of the following CPU scheduling algorithms cannot be preemptive?

• A. Round Robin
• B. Shortest Remaining Time First
• C. First Come First Served
• D. Priority Scheduling

Hint:

FCFS is the simplest scheduling algorithm but often suffers from the "Convoy Effect," where small processes wait behind a very long process.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
CPU scheduling algorithms are classified as Preemptive or Non-preemptive. In preemptive scheduling, the OS can interrupt a running process to allocate the CPU to another. In non-preemptive scheduling, a process keeps the CPU until it terminates or switches to a waiting state.
Step 2: Detailed Explanation:
- Round Robin: Inherently preemptive as it uses time quantums.
- Shortest Remaining Time First (SRTF): This is the preemptive version of Shortest Job First (SJF).
- Priority Scheduling: Can be either preemptive or non-preemptive.
- First Come First Served (FCFS): This is a strictly non-preemptive algorithm. Once the CPU is allocated to a process, it cannot be taken back until the process completes its burst.
Step 3: Final Answer:
FCFS is always non-preemptive.