Question

In Operating Systems, which of the following CPU scheduling algorithms is strictly non-preemptive?

• A. Round Robin
• B. Shortest Remaining Time First
• C. First-Come, First-Served (FCFS)
• D. Priority Scheduling (Preemptive)

Hint:

Non-preemptive algorithms (like FCFS) are easier to implement and have less overhead, but they can suffer from the "Convoy Effect," where short processes wait behind a long process.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
We need to identify which of the given CPU scheduling algorithms does not support preemption (i.e., once a process starts executing, it cannot be interrupted until it finishes or performs I/O).


Step 2: Detailed Explanation:
Let us evaluate each scheduling algorithm:
- Round Robin (RR): This is inherently a preemptive algorithm. It uses a time quantum, and processes are forcefully preempted if they exceed their allotted time.
- Shortest Remaining Time First (SRTF): This is the preemptive version of Shortest Job First (SJF). If a new process arrives with a shorter execution time than the currently running process, the current process is preempted.
- First-Come, First-Served (FCFS): This is the simplest scheduling algorithm. Processes are assigned to the CPU in the order they arrive. Once a process gets the CPU, it keeps it until it terminates or blocks. Therefore, it is strictly non-preemptive.
- Priority Scheduling (Preemptive): As the name specifies in the option, this version is preemptive.
Thus, FCFS is the only strictly non-preemptive algorithm among the choices.


Step 3: Final Answer:
The correct choice is (C).