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Disk requests come in to the d

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Disk requests come in to the disk driver for cylinders 10,22,20,2,40,6, and 38, in that order. In all cases, the arm is initially at cylinder 20. A seek takes 6 msec per cylinder moved. How much seek times is needed for

(1) First Come First Served (FCFS).

(2) Shorted Seek Time First (SSTF).
(3) Elevator algorithm (SCAN, initially moving upward)
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(1) FCFS

柱面访问序列： (20),10,22,20,2,40,6,38

磁盘臂访问序列： (20),10,22,20,2,40,6,38

(10+12+2+18+38+34+32)X6 = 876msec

(2) SSTF

柱面访问序列： (20),10,22,20,2,40,6,38

磁盘臂访问序列： 20,22,10,6,2,38,40

(2+12+4+4+36+2)X6 = 360msec

(3) elevator

柱面访问序列： (20),10,22,20,2,40,6,38

磁盘臂访问序列： 20,22, 38,40,10,6,2

(2+16+2+30+4+4)X6 = 348msec

发表于 2017-05-17 01:17:48 回复(0)
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