OS

Question

Which of the following disk scheduling policies results in the minimum amount of head movement?

(A) FCFS
(B) Circular scan
(C) Elevator

Answer 1

Amount of head movement will depend on scheduling policies as well as request order..still circular scan seem to be better choice...

Answer 2

This will depend the order of Track requested.
FCFS : complete the first cum first serve  
C-scan: completes whatever it comes in its moving direction then goes back to starting point or end point & again start from there. 
Elevator(Scan):completes whatever it comes in its moving direction the reverse back and completes the left request. 
Let us consider head is now at 53 and moving forward  and request of track are 

1. 65 75 85 89 99 in this all will give same head movement 
2. 75 65 85 99 in this elevator and c-scan gives the same and FCFS will give on extra.
3.44 65 51 74 84 99 in this FCFS  = 4 head movement 
                                       C-scan = 2
                                       Elevator(scan) = 1
so we can say Elevator gives min head movement.

Answer 3

SCAN (Elevator) will be the answer.

Answer 4

Circular scanning works just like the elevator to some extent. It begins its scan toward the nearest end and works its way all the way to the end of the system. Once it hits the bottom or top it jumps to the other end and moves in the same direction. Circular SCAN has more head movement than SCAN (elevator) because Circular SCAN has circular jump and it does count as a head movement.
SCAN (elevator) is the best choice here.

Source: https://www.geeksforgeeks.org/operating-systems-input-output-systems-question-5/