Operating system

Assume a multiprogramming system (1 CPU) and 3 I/O processors. Assume only 3 processes will run on the system simultaneously. The use of CPU and I/O by each process is shown below. All processes arrived in this order: A, B, C. Assume the O/S requires 2 cycles each invocation. No other processes will appear in the system until all processes are finished. Default Quantum is 5 units. Service requests are processed prior to time outs. All I/Os are started on second cycle just as in the example provided. What time units will each process finish? Assume first come first serve Round Robin in the ready state (INITIAL ORDER IS A,B,C). Note: The last 2 cycles are for O/S.

A: 5 cpu, 15 i/o, 10 cpu

B: 15 cpu

C: 5 cpu, 6 i/o, 4 cpu, 8 i/o, 5 cpu

Process

|

A |

|

B |

|

C |

|

O/S|

|

+....+....+....+....+....+....+....+....+....+....+....+....+....+....+

1 1 2 2 3 3 4 4 5 5 6 6 7

0 5 0 5 0 5 0 5 0 5 0 5 0 5 0

NOTE: Horizontal-line=CPU, Zig-Zag-line=I/O, |=End-Unit-Period, ]=Done

(1 Point each):

1) When will A finish: ___

2) When will B finish: ___

3) When will C finish: ___

4) How many cycles did the O/S get to process these processes: ___

5) Could the O/S itself be interrupted requiring more O/S cycles? _____