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Operating systems MCQ interview questions - Set 8

1. The difference between preemptive and non-preemptive scheduling is

(a) Whether or not a ready process can be involuntarily terminated

(b) Whether or not a running process is involuntarily removed from the ready state

(c) Whether or not a blocked process can have its resources involuntarily taken away from it

(d) Waiting time is more in preemptive scheduling and less in non-preemptive

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Ans : (b)

Answer: (b)            Preemptive scheduling - Processor can be preempted to execute a different process in the middle of execution of any current process. Non-preemptive scheduling - Once Processor starts to execute a process it must finish it before executing the other. It cannot be paused in middle.

2. The four conditions that must hold in order for deadlock to occur are

(a) Mutual exclusion, hold-and-wait, circular wait, and no preemption

(b) No preemption, no starvation, circular wait, and mutual exclusion

(c) Hold-and-wait, circular wait, no starvation and mutual exclusion

(d) All of the above

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Ans : (a)

Answer: (a)             What are the four conditions that are necessary and sufficient to cause a deadlock? Mutual exclusion - At least one process must be held in a non-sharable mode. At least one non-sharable resource in the system which can be used by only one process at a time. Hold and wait – there must be a process holding one resource and waiting for another. Circular wait – there exist a set of circular chain of processes with each process holding resources which are currently being requested by the next process in the chain. No preemption – Resources cannot be preempted. Previously granted resources cannot forcibly taken away

3. When does preemption take place?

(a) When a quantum expires.

(b) When a process issues an I/O request.

(c) When a process exits.

(d) All of the above.

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Ans : (a)

Answer: (a)             Preemption means the operating system moves a process from running state to ready state without the process requesting it. Preemption takes place when a process switches from the running state to the ready state due to timer interrupt (time slice or quantum), or when a process switches from the waiting state to the ready state due to the completion of I/O.

4. What does interrupt do?

(a) Allow the CPU to notify devices that it needs attention

(b) Allow the devices to notify the device controller that they need attention

(c) Allow the devices to notify the CPU that they need attention

(d) None of the above

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Ans : (c)

Answer: (c)             An interrupt is a signal to the processor emitted by hardware or software indicating an event that needs immediate attention.

5. In contrast to a cooperative scheduler, a preemptive scheduler supports the following state transition

(a) Ready → running

(b) Running → ready

(c) Ready → blocked

(d) Blocked → running

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Ans : (b)

Answer: (b)            Cooperative scheduler is the non-preemptive scheduler. Preemption means the operating system moves a process from running to ready without the process requesting it. Ready → blocked or blocked → running are not valid state transitions. Ready → running is a state transition that happens both in preemptive and non-preemptive scheduling. Running → ready is supported by preemptive scheduler.

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