GATE 2026 CS2 Q.23: solution and answer

Official answer: BSource: Official answer key, GATE 2026 CS2 (IIT Guwahati)

1. A scheduling algorithm is preemptive if the CPU can be taken from a running process before its burst ends, either on a timer interrupt or when a better candidate arrives. Check each option against this.

2. SRTF is the preemptive form of shortest job first. A newly arrived process whose burst is shorter than the running process's remaining time takes the CPU. So SRTF is preemptive by definition.

3. Round Robin gives each process a time quantum. When the quantum expires the running process is moved to the back of the ready queue. This is preemption by the timer, so Round Robin is preemptive.

4. Priority Scheduling has both a preemptive and a non-preemptive version. In the preemptive version, a higher-priority arrival displaces the running process. So it can be preemptive.

5. FCFS always runs the process that arrived earliest, and runs it until it finishes or blocks. A later arrival always has a later arrival time, so it can never displace the running process. No timer or priority rule exists to take the CPU away, so FCFS cannot be preemptive. The answer is (B).