Q18) (Input / Output) Disk requests come in to the disk driver for different cylinders during times given in the below table. Assuming all files are of the same size, a data read takes 6 msec per request and moving the disk head by one cylinder takes 1 msec. Assuming the disk head is initially at cylinder 20, how much seek time is needed for: (Justify your answers for partial credits)

Time (msec)	Cylinder Request	Time (msec)	Cylinder Request
0	10	27	20
22	11	28	2
24	17	29	40
25	12	40	6
26	22	41	38

(a) (5 pts) First-come, first served.

(b) (5 pts) Closest cylinder next.

(c) (5 pts) Elevator algorithm (initially moving upward).

(d) (5 pts) Elevator algorithm starting from cylinder 0 (initially moving upward).