GATE CS 2020 Q.22 (CS Q.12): CPU Scheduling

Consider the following statements about process state transitions for a system using preemptive scheduling.

I. A running process can move to ready state.
II. A ready process can move to running state.
III. A blocked process can move to running state.
IV. A blocked process can move to ready state.

Which of the above statements are TRUE?

I, II, and III only

II and III only

I, II, and IV only

I, II, III, and IV

Official answer and solution

Official answer: C
From: Official GATE 2020 answer key

Solution

Identify valid process state transitions in a preemptive multitasking operating system.

Consider the standard process state model:

Transition I (Running $\to$ Ready): A running process is preempted by the scheduler (for instance, when its time slice expires or a higher priority process becomes ready). This is TRUE.
Transition II (Ready $\to$ Running): The CPU scheduler selects a process from the ready queue and dispatches it to the CPU. This is TRUE.
Transition III (Blocked $\to$ Running): A blocked process waits for an event (such as I/O completion). When the event occurs, the process transitions to the Ready state to await scheduling; it cannot jump directly to Running. This is FALSE.
Transition IV (Blocked $\to$ Ready): When an I/O operation or waited-for event completes, the operating system moves the process from the blocked queue to the ready queue. This is TRUE.

Therefore, statements I, II, and IV only are TRUE.

Final answer

The answer is the one in the official GATE answer key. The solution is this site's own explanation.

Source

Paper: GATE 2020 Computer Science and Information Technology (CS)
Question: 22 of 65, printed as CS Q.12
Section: Computer Science and Information Technology

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