Suppose that a disk drive has 2,000 cylinders numbered 0 to 1999. The drive is currently serving a request at cylinder 142, and the previous request was at cylinder 125. The queue of pending requests in FIFO order is:

86, 1470, 913, 1774, 948, 1509, 1022, 1750, 130.

Starting from the current head position, what is the total distance (in cylinders) that the disk arm moves to satisfy all the pending requests for the following disk scheduling algorithm Scan

7080

Explanation:

Let totaldistanceincylinders (total seek distance)=x=0

Its  

     142-86=56                  x=56

      1470-86=1384                      x= 56+ 1384=1440

      1470-913= 557             x= 1440+557= 1997

      1774-913=861                    x= 1997+ 861=2858

      1774-948= 826              x=2858+826=3684

      1509-948=561             x=3684+561=4245

      1509-1022=    487        x=4245+487=4732

      1750-1022=728          x=4732+728=5460

      1750-130=1620          x=5460+1620=7080

       hence, total distance in cylinders = 7080

This is the total seek distance.