19、Disk requests come in to the disk driver for cylinders 10, 22, 20, 2, 40, 6, and 38, in that order. A seek takes 6 ms

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19、Disk requests come in to the disk driver for cylinders 10, 22, 20, 2, 40, 6, and 38, in that order. A seek takes 6 msec per cylinder. How much seek time is needed for
(a) First-come, first served.
(b) Closest cylinder next.
(c) Elevator algorithm (initially moving upward).
In all cases, the arm is initially at cylinder 20.
20、Disk requests come in to the disk driver for cylinders 8, 18, 20, 2, 38, 6, and 32, in that order. A seek takes 6 msec per cylinder. How much seek time is needed for
(a) First-come, first served.
(b) Closest cylinder next.
(c) Elevator algorithm (initially moving upward).
In all cases, the arm is initially at cylinder 20.