Identify the circumstances under which pre-emptive CPU scheduling is used:
(a) A process switches from Running state to Ready state
(b) A process switches from Waiting state to Ready state
(c) A process completes its execution
(d) A process switches from Ready to Waiting state
Choose the correct option:
(A)
(a) and (b) only
(B)
(a) and (d) only
(C)
(c) and (d) only
(D)
(a), (b), (c) only
Answer: (A)
Explanation:
Preemptive scheduling is used when a process switches from running state to ready state or from the waiting state to ready state. The resources (mainly CPU cycles) are allocated to the process for a limited amount of time and then taken away, and the process is again placed back in the ready queue if that process still has CPU burst time remaining. That process stays in the ready queue till it gets its next chance to execute.
So that option 1 is correct.
1. A process switches from Running state to Ready state
2. A process switches from Waiting state to Ready state
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