fcfs

When multiple I/O requests arrive for disk access, we need a simple, fair way to decide the order of servicing them.

FCFS (First Come First Serve) processes disk I/O requests in the exact order they arrive, like a queue at a store.

1. Request queue maintains arrival order
2. Disk arm services requests in FIFO order
3. No reordering or optimization

• Simplest disk scheduling algorithm
• Fair (no starvation)
• Can be very inefficient (long seek times)
• Example: queue [100, 50, 150, 30] → services in that order

• Built from: Disk Scheduling, Disk Structure
• Builds into: SSTF, SCAN
• Related: Disk Structure
• Contrasts with: SSTF (optimizes vs simple FIFO)

• Can cause wild swings across disk (poor performance)
• No consideration of seek distance
• Simple but often impractical for real systems