Compute the average traveling distance in the following IO p

Compute the average traveling distance in the following I/O problem using SCAN and SSTF scheduling. The I/O queue has the following requests: 64, 12, 55, 85, 14, 36, 62, 45, 24. The R/W heads are currently positioned at track 50.  

Solution

The I/O queue has the following requests: 64,12,55,85,14,36,62,45,24

current position of R/W heads = track 50

SCAN

50 -----> 55 (5)

55----->62 (7)

62 ----->64 (2)

64 ------> 85 (21)

45 <--------- 85 (40)

36 <--------- 45 (9)

24 <--------- 36 (12)

14 <--------- 24 (10)

12 <------- 14 (2)

Total distance covered = 5+7+2+21+40+9+12+10+2 = 108

Average distance = 108/9 = 12

SSTF(Shortest Seek Time First)

50 -----> 55 (5)

55 ------> 62 (7)

62 ----> 64 (2)

45 <------ 64 (19)

36 <------ 45 (9)

24 <-------- 36 (12)

14 <-------- 24 (10)

12 <------- 14 (2)

12 ---------->85 (73)

Total distance = 5+7+2+19+9+12+10+2+73 =139

Average distance 139/9 = 15.33