45, 81, 185, 33, 175, 99, 150, 77
(Consider that the head starts from location 58)
FCFS Disk Scheduling Explained
Disk scheduling algorithms manage the order in which read/write requests to a disk are serviced. The First-Come, First-Served (FCFS) algorithm is the simplest approach. It processes requests strictly in the order they arrive in the queue, without prioritizing based on location.
FCFS Request Sequence and Head Movement
The initial position of the disk head is at cylinder 58. The requests arrive in the following sequence:
- 45
- 81
- 185
- 33
- 175
- 99
- 150
- 77
To calculate the total head movement using FCFS, we track the head's movement from its starting position to the first request, and then sequentially to each subsequent request in the given order.
Step-by-Step Head Movement Calculation
The total head movement is the sum of the absolute differences between consecutive locations visited by the disk head.
Starting Position: 58
| Current Position | Next Request | Head Movement (Cylinders) |
| 58 | 45 | $|45 - 58| = 13$ |
| 45 | 81 | $|81 - 45| = 36$ |
| 81 | 185 | $|185 - 81| = 104$ |
| 185 | 33 | $|33 - 185| = 152$ |
| 33 | 175 | $|175 - 33| = 142$ |
| 175 | 99 | $|99 - 175| = 76$ |
| 99 | 150 | $|150 - 99| = 51$ |
| 150 | 77 | $|77 - 150| = 73$ |
Total Head Movement Calculation
Now, we sum the individual head movements calculated in the previous step:
Total Movement = $13 + 36 + 104 + 152 + 142 + 76 + 51 + 73$
Total Movement = 647 cylinders
Therefore, using the FCFS disk scheduling method, the total head movement required to service all the requests starting from cylinder 58 is 647 cylinders.
Important Questions from Disk Scheduling
Which of the following is the time taken to move an access arm to a certain track on a disk?
Move the Read/Write head of disk in or out to position on a correct track is known as ______.
_______ is a process of lifting the process from memory and placing it on disk.
- Match List I with List II
List I List II A. RAID Level 2 I. Block interleaved distribution parity B. RAID Level 3 II. Also known as P+Q redundancy Scheme C. RAID Level 5 III. Bit interleaved parity D. RAID Level 6 IV. Also known as Memory style error correcting code organization
Choose the correct answer from the options given below: - What will be the total head movement of cylinders for the SSTF disc Scheduling technique ?
