Tuesday, 31 October 2017

Net 40


Q. Consider a disk queue with request for input/output to block on cylinders
98, 183, 37, 122, 14, 124, 65, 67
in that order. Assume that disk head is initially positioned at cylinder 53 and moving towards cylinder number 0. The total number of head movements using Shortest Seek Time First (SSTF) and SCAN algorithms are respectively

(A) 236 and 252 cylinders
(B) 640 and 236 cylinders
(C) 235 and 640 cylinders
(D) 235 and 252 cylinders

Ans: (Current ans. is 208 & 236 which not given in option)


SSTF Algorithm when movement to 0 given:
Total head movements=16+23+51+2+31+24+2+59=208.

SCAN Algorithm:
Total head movements=   16+23+14+65+2+31+24+2+59=236
SSTF Algorithm when movement to 0 not given:

Total head movements=12+2+30+23+84+24+2+59=236.

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