SCAN has uneven wait times — requests just passed when the arm reverses have to wait a full cycle. Can we make wait times more uniform?
C-SCAN (Circular SCAN) services requests in one direction only, then jumps back to the beginning without servicing requests on the return trip.
- Move disk arm in one direction (e.g., inward)
- Service all requests in that direction
- When reaching end, jump back to start
- Continue in same direction (no reverse)
- Circular — never reverses direction
- More uniform wait times than SCAN
- No reversal = simpler logic
- Wastes time on return jump (no service)
- Better for systems needing predictable latency
- Built from: Disk Scheduling, SCAN
- Builds into: LOOK, C-LOOK
- Related: Disk Structure
- Contrasts with: SCAN (one direction vs reverse)
- Return jump wastes time (no requests serviced)
- Still may not be optimal for all workloads
- Good for real-time systems (predictable)