Question

2. (22 points) Given that it takes 1.75 ms to travel from one track to the next of a hard drive; that the arm is originally positioned at Track 15 moving toward the low- numbered tracks; and that you are using the LOOK scheduling policy: Compute the total seek time to satisfy the following requests 4, 40, 35, 11, 14, and 7. Assume all requests are initially present in the wait queue. (Ignore rotational time and transfer time; just consider seek time.)

Answer 1

The requests are serviced as follows:

15 --> 14 --> 11 --> 7 --> 4 --> 35 --> 40

Total track movements = (15 - 14) + (14 - 11) + (11 - 7) + (7 - 4) + (35 - 4) + (40 - 35)

                                       = 1 + 3 + 4 + 3 + 31 + 5

                                       = 47

Total Time = total movements * time/movement

                  = 47 * 1.75

                  = 82.25 ms