GATE CS 2024 Set 1 — Question 25

MSQ+1 / -0EasyProcess States & PCBProcesses & ThreadsOperating System

Operating System → Processes & Threads → Process States & PCB

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Question

Which of the following process state transitions is/are NOT possible?
A.
Running to Ready
B.
Waiting to Running
C.
Ready to Waiting
D.
Running to Terminated

Correct answer

(B) Waiting to Running; (C) Ready to Waiting

Solution

In a standard five-state process transition model (New, Ready, Running, Waiting, Terminated):
1.Running to Ready: This is a possible transition. It occurs when a process is preempted (e.g., its time quantum expires in a Round Robin scheduling algorithm).
2.Waiting to Running: This is NOT possible. A process in the Waiting (or Blocked) state must first transition to the Ready state once the event it was waiting for (like I/O completion) occurs. From the Ready state, the CPU scheduler can then dispatch it to the Running state.
3.Ready to Waiting: This is NOT possible. A process can only enter the Waiting state from the Running state. This happens when the process makes a system call for an I/O operation or needs to wait for a specific event to occur.
4.Running to Terminated: This is a possible transition. It occurs when a process finishes its execution or is terminated due to an error.
Therefore, the transitions that are not possible are (B) and (C).

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