Question

1. Assume that at time 5 no system resources are being used except for the processor and memory and every process (1,3) is either in ready queue (ready to run) or at CPU. Now consider the following events: (Hints: if a process executes something, it is on CPU at the point, if a process going to do IO or create a process, it needs to give out CPU immediately, if a process is time-out, an event will occur and listed here.)

At time 5: P1 executes a command to read from disk unit 3.

At time 20: P3 executes a command to read from disk unit 2.

At time 33: An interrupt occurs from disk unit 2: P3's read is complete.

At time 36: An interrupt occurs from disk unit 3: P1's read is complete.

At time 48: P3 terminates

At Time 52: P1 terminates

For each time 22, 37, and 47, identify which state each process is in. If a process is blocked, further

identify the event on which is it blocked.

Answer 1

Let's consider the system at time t = 22.

At this time, we only have to consider the first two instructions.

At time 5: P1 executes a command to read from disk unit 3.

At time 20: P3 executes a command to read from disk unit 2.

So, at time t = 22, both processes P1 and P3 will be blocked for I/O.

Let's consider the system at time t = 37. We now have to consider the next two instructions.

At time 33: An interrupt occurs from disk unit 2: P3's read is complete.

At time 36: An interrupt occurs from disk unit 3: P1's read is complete.

Now both processes have finished reading data from the respective disk units. Hence, at this time both of them would be in the running state.

Let's consider the system at time t = 47. No new instruction has occurred between t = 37 and t = 47. Hence, both P1 and P3 would still be in the running state.

Let me know if you have any doubts in the comments.