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:
A scheduling algorithm is preemptive if the OS can interrupt a running process to allocate the CPU to another. It is non-preemptive if a process keeps the CPU until it voluntarily releases it (finishes or blocks).
Step 2: Detailed Explanation:
- Round Robin (RR): Uses a time quantum to switch between processes. It is always preemptive.
- Shortest Remaining Time First (SRTF): This is the preemptive version of Shortest Job First (SJF). It is always preemptive.
- First Come First Served (FCFS): Processes are executed in order of arrival. Once a process starts, it runs to completion. It is inherently non-preemptive.
- Priority Scheduling: Can be implemented as either preemptive or non-preemptive.
Step 3: Final Answer:
FCFS is the only one in the list that is strictly non-preemptive.