The head of a hard disk serves requests following the shortest seek time first (SSTF) policy. The head is initially positioned at track number 180.
What is the maximum cardinality of the request set, so that the head changes its direction after servicing every request if the total number of tracks are 2048 and the head can start from any track?
(A) 9
(B) 10
(C) 11
(D) 12
Answer: (C)
Explanation: Distance of SSTF changing – >
| 1 | 3 | 7 | 15 | 31 | 63 | 127 | 255 | 511 | 1023 | 2047 |
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 |
Head is changing it’s direction after servicing every request. Maximum Cardinality is thus 11
180->181->178->185->170->201->138->265->10