Two processors: priority and RR (q=3)

Assumptions: both processors are identical and share one ready queue; a process may run on either processor; priority 1 is the highest; ties are broken by earlier arrival; context-switch time is zero. In round robin a process arriving at the same instant a quantum ends joins the queue before the preempted one.

1. Preemptive priority

At every instant the two highest-priority ready processes run on the two CPUs. A new process of higher priority preempts the lowest-priority running one. (A and F, both priority 1, hold the CPUs whenever present; F arrives at 8 and preempts B.)

CPU1
| A | B | D | H | C |
0   12  14  23  27  34
CPU2
| idle | B | F | E | I | G |
0      2   8   13  19  21  28

Average waiting time = 95/9 = 10.56; average turnaround time = 155/9 = 17.22

2. Round Robin (q = 3)

Both CPUs take processes from the head of a single FIFO queue; each runs at most 3 ms and then goes to the tail.

CPU1
| A | D | A | I | C | D | F | E | B | G | A |
0   3   6   9   11  14  17  20  23  25  28  31
CPU2
| idle | B | H | E | B | G | H | A | C | D | F | C |
0      2   5   8   11  14  17  18  21  24  27  29  30
| G |
30  31

Average waiting time = 129/9 = 14.33; average turnaround time = 189/9 = 21

Answer: Preemptive priority: AWT = 10.56 ms, ATAT = 17.22 ms. Round robin (q=3): AWT = 14.33 ms, ATAT = 21 ms.