Suppose that a disk drive has 5000 cylinders,numbered 0 to 4999.The drive is currently Serving a request at cylinder 143,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 current head position,what is a total distance(in cylinders) that the Disk arm move to satisfy all a pending requests,for each of the following disk Scheduling algorithms?

1.FCFS 2.SSTF 3.SCAN 4.LOOK.

Solution:

(1) FCFS:

• The FCFS algorithm just follows the order of the requests given.

• The FCFS schedule is: 143, 86, 1470, 913, 1774, 948, 1509, 1022, 1750, 130

• Movements: 57 + 1384 + 557 + 861 + 826 + 561 + 487 + 728 + 1620

• The total distance is: …