A disk takes 1 ms per track seek time, and the head is currently on track 70. Assume it takes 5 ms to service a request once the head is at the right track. The following set of requests are pending, given as (ID, track) in order of arrival. How much time does it take to service all the requests if the Elevator algorithm is used and the current direction is down?

Total time = 190 ms

Explanation:

The requests missing in question are:

Requests ( A, 80) , (B,75) , (C,82) , (D,90) , (E,45)

Number of movements = | 70 - 45 | +  | 45 - 0 | +  | 0 - 75 | +  | 75 - 80 | +  | 80 - 82 | +  | 82 - 90 |

= 35 + 45 + 75 + 5 + 2 + 8

= 70 + 80 + 10

= 160

Time taken for seek = 160 * 1 ms = 160 ms

Time taken for servicing request = Number of tracks * Time for each track = 5*6 = 30

Total time = 160 + 30 = 190 ms.  

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