Consider that requests to read the following set of logical block numbers are en

Question

Consider that requests to read the following set of logical block numbers are enqueued to be serviced from a disk that has 100 logical blocks laid out sequentially from block 0 to block 99. {1, 22, 14, 86, 32, 11, 66, 45, 80} Assume that the seek time in moving the disk arm head from logical block i to block j is proportional to |i - j|. Given that the arm head is currently positioned at block 34 and is in the midst of moving in the direction towards block 99, what is the sequence in which the enqueued blocks will be read with the i) SSTF, ii) SCAN, and iii) C-SCAN algorithms?

Explanation / Answer

request queue = {1,22,14,86,32,11,66,45,80}

i) SSTF

head movement

34----45 =11

45----32 = 13

32----22 =10

22----14 =12

14----11 = 3

11----1 =10

1----66 =65

66----80 = 14

80----86 = 6

Total Head movement = 144

ii) SCAN

Head Movement

34 -----45 =11

45 ----- 66 = 21

66-----80 = 14

80 ------86 = 6

86------32 = 54

32-----22 = 10

22-----14 = 8

14-----11 = 3

11-----1 = 10

Total Head Movement = 137

iii) C-SCAN

Head Movement

34---45 = 11

45----66 = 21

66-----80 =14

80-----86 = 6

86-----99 = 13

99-----0 not included

0------1 =1

1------11 = 10

11------14 = 3

14-----22 = 8

22------32 = 10

Total Head Movement = 97

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