Which of the following is not a CPU scheduling Algorithm?

Concept

An operating system uses different families of scheduling algorithms for different resources. A CPU scheduling algorithm decides the order in which ready processes are given the processor (minimising waiting/turnaround time), whereas a disk scheduling algorithm decides the order in which pending read/write requests are served by the disk arm (minimising seek time). The two solve unrelated problems, so an algorithm belongs to exactly one family.

Applying it here

Classify each listed algorithm by the resource it manages:

• FCFS (First Come First Served) — orders processes for the CPU by arrival time. CPU scheduling.

• SJF (Shortest Job First) — picks the ready process with the shortest next CPU burst. CPU scheduling.

• SJN (Shortest Job Next) — only a second name for SJF; same CPU-scheduling policy.

• C-SCAN (Circular SCAN) — moves the disk arm in one direction servicing requests, then jumps back to the start. This manages the disk arm, not the processor — disk scheduling.

Conclusion

Three of the four (FCFS, SJF and its synonym SJN) manage the CPU, so the one that is not a CPU scheduling algorithm is C-SCAN, which is a disk scheduling algorithm.