Note that some of the data in this problem is different from the similar problem
ID: 3732043 • Letter: N
Question
Note that some of the data in this problem is different from the similar problem in the textbook. Given that it takes 0.90 ms to travel from one track to the next of a hard drive; that the arm is originally positioned at Track 12 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, 38, 11, 14, and 7. Assume all requests are initially present in the wait queue. (Ignore rotational time and transfer time; just consider seek time.). In addition, EXPLAIN below the table why the policy handled the requests the way it did. This question is worth 24% of the assignment, 20% for table data and 4% for your explanation.
From
To
# of Tracks
TOTAL
Total ms
From
To
# of Tracks
TOTAL
Total ms
Explanation / Answer
Time = 0.90ms
Total seek time= —4, 40, 38, 11, 14, and 7
Path ranges
12-4
4-11
11-38
38-40
40-14
14-7
TABLE:
In LOOK scheduling policy the arm moves as long as final request in one direction direction and then it reverses direction immediately without going all the way to the end of the disk. Thus, using this we find the seek time is equal to
=[(12-14)+(14-11)+(11-7)+(7-4)+(38-4)] *0.90
=[-2+3+4+3+34]*0.90 =42*0.90 = 37.8 ms
FROM TO TRACK 12 14 -2 14 11 3 11 7 4 7 4 3 38 4 34 TOTAL 42*0.90ms TOTAL ms 37.8msRelated Questions
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