Unformatted text preview: (once the seek has been performed is the rotational delay (one half of a rotation) plus 22 / 256 of a rotation. Thus, the total cost is 2560(9 . 5 + 11 . 11(0 . 5 + 22 / 256)) ≈ 40 , 985 ms. This is far more expensive than storing the f le in adjacent tracks. 8.6 Considering all of the possible cases for a disk with n tracks, the f rst track could be at any position from 1 to n , and the second track could be at any position from 1 to n . If the f rst track is i and the second is j , then the distance is  j − i  . Alternatively, in n of the n 2 possible cases the distance is 0, and otherwise we can count only the cases where i < j and multiply the sum by two to account for the cases where j < i . Thus, we get the average cost as 2 ∑ n i =1 ∑ n j = i +1 ( j − i ) n 2 = 2 ∑ n − 1 i =1 ∑ i j =1 ( j ) n 2 = 2 ∑ n − 1 i =1 ( i 2 + i ) / 2 n 2 = 1 n 2 ( n − 1 X i =1 i 2 + i ) =...
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 Fall '08
 BELL,D

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