Question

In the various CPU scheduling algorithms we have studied thus far, when does
preemption occur? Circle the best answer.
(a) When a pre-defined timeslice expires
(b) When a process changes its state to being blocked on I/O
(c) When a higher-priority process arrives and wants to use the CPU
(d) Both (a) and (b), but not (c)
(e) Both (b) and (c), but not (a)
(f) Both (a) and (c), but not (b)

Answer 1

The answer is (f) both (a) and (c) but not (b).

Preemptive multitasking involves interrupting the currently running process and selecting a different one from the waiting pool so that all processes get some CPU time at any given moment. Nowadays, all operating systems support Preemptive multitasking.

Multitasking is achieved by,

(a)Timeslicing, where a process runs uninterrupted for a period of time(timeslice or quantum)and as the timeslice expires a scheduler is run to choose the next effective process to utilize the CPU.

(c)Context switch, where the state of the current process is stored before switching the CPU to a newly arrived high priority process.

option (b) is not valid because the scenario applies to non-preemptive multitasking systems, where the current process volantarily handovers the CPU to other processes inorder to run concurrently.