Disk Scheduling Calculator (FCFS, SSTF, SCAN, C-SCAN, LOOK)
Disk head scheduling with FCFS, SSTF, SCAN, C-SCAN, LOOK and C-LOOK: seek order, each move, total head movement, average seek and a head-position chart.
SCAN and C-SCAN travel to the edge of the disk (0 or 199) before turning only when requests remain on the other side; LOOK and C-LOOK turn at the last request.
Ties in SSTF go to the lower cylinder.
| Step | From | To | Distance | Note |
|---|---|---|---|---|
| 0 | 53 | 53 | 0 | start |
| 1 | 53 | 37 | 16 | serve |
| 2 | 37 | 14 | 23 | serve |
| 3 | 14 | 0 | 14 | end of disk |
| 4 | 0 | 65 | 65 | serve |
| 5 | 65 | 67 | 2 | serve |
| 6 | 67 | 98 | 31 | serve |
| 7 | 98 | 122 | 24 | serve |
| 8 | 122 | 124 | 2 | serve |
| 9 | 124 | 183 | 59 | serve |
| Algorithm | Total movement | Average seek |
|---|---|---|
| FCFS | 640 | 80 |
| SSTF | 236 | 29.5 |
| SCAN | 236 | 29.5 |
| C-SCAN | 386 | 48.25 |
| LOOK | 208 | 26 |
| C-LOOK | 326 | 40.75 |
A hard disk serves requests for different cylinders, and the order in which it visits them decides how far the read/write head travels. This calculator runs the six classic disk-scheduling algorithms — FCFS, SSTF, SCAN (elevator), C-SCAN, LOOK and C-LOOK — on your request queue and starting position, and shows the seek order, every move, the total head movement and the average seek, plus a chart of the head position and a comparison of all six.
How to use this tool
- Enter the queue of requested cylinders.
- Enter the starting head position and the number of cylinders.
- Choose the algorithm and the direction the head is moving.
- For C-SCAN and C-LOOK, decide whether the return jump counts; read the totals.
Formula
total head movement = Σ |next cylinder − current cylinder| · average seek = total ÷ number of requests
FCFS serves requests in arrival order; SSTF always picks the nearest pending request; SCAN sweeps to the edge of the disk and back; LOOK turns at the last request instead of the edge; C-SCAN and C-LOOK serve in one direction only and jump back to the start. Courses differ on whether that return jump counts as head movement, so it can be included or left out. Tied distances in SSTF go to the lower cylinder.
Example
For the textbook queue 98, 183, 37, 122, 14, 124, 65, 67 with the head at 53 on a 200-cylinder disk, SCAN moving toward 0 goes 53 → 37 → 14 → 0 and then up to 183: 236 cylinders, an average of 29.5 per request. SSTF also gives 236, FCFS 640, and C-SCAN moving up 382 (183 without the return jump).
Frequently asked questions
Why does SSTF have the same total as SCAN here?
Coincidence of this queue. SSTF is greedy and can starve requests at the far end of the disk; SCAN guarantees every request is reached within two sweeps.
Should the C-SCAN return count?
It depends on the course. The head does physically move back, which is why it is counted by default here, but some textbooks treat the return as a fast seek and leave it out — switch the option to match.
Does this apply to SSDs?
No. SSDs have no moving head, so seek order does not matter; these algorithms concern spinning disks.
Sources
Last updated:
Page address with these inputs: https://kakao.mobile/tools/disk-scheduling-simulator/
Cite or embed this tool
kakaoCalc. (2026, November 8). Disk Scheduling Calculator (FCFS, SSTF, SCAN, C-SCAN, LOOK). https://kakao.mobile/tools/disk-scheduling-simulator/
“Disk Scheduling Calculator (FCFS, SSTF, SCAN, C-SCAN, LOOK).” kakaoCalc, 8 Nov. 2026, kakao.mobile/tools/disk-scheduling-simulator/.
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