Question

Suppose in a time-shared operating system, a certain process is performing I/O. It must be in which one of the following states?

• A. Ready
• B. Blocked
• C. Terminating
• D. Running

Hint:

If a process is waiting for any event like I/O completion, it is always in the Blocked or Waiting state.

Answer 1

The Correct Option is B

A process moves through Ready, Running, Blocked and Terminated states depending on what it is doing. Ready means it's waiting only for CPU time; Running means the CPU is executing it right now; Blocked means it's waiting on something other than the CPU, like an I/O device; Terminated means it has finished.
Once a process asks the I/O subsystem to read or write data, the CPU can't usefully continue running it since the result of the I/O isn't available yet, so the OS sets it aside and gives the CPU to another process. That "set aside, waiting on I/O" condition is precisely the Blocked state.
So the correct answer is Blocked.

Answer 2

Think of this in terms of the process state-transition diagram used in OS design, where a process moves between states based on specific triggering events:

1. Ready: reached from Blocked when an I/O completes, or from Running when the scheduler preempts a process. It is a "waiting for CPU" state, not a "waiting for a device" state, so it doesn't describe a process currently doing I/O.
2. Blocked: reached from Running the moment a process issues an I/O or event-wait request, and left only when that I/O completes. This transition (Running to Blocked, triggered by an I/O request) is exactly what happens to the process in the question.
3. Terminating: reached from Running when a process completes its execution entirely; there is no transition into this state from an I/O request.
4. Running: a process leaves the Running state the instant it makes an I/O call, since the CPU cannot sit idle waiting on hardware, it switches to another process.

Tracing the transition triggered by "process requests I/O" leads directly to one state.

Therefore, the correct answer is Blocked.