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A Quick Abstract:

1. Introduction to Disk Scheduling:

Disk scheduling is a crucial aspect of operating systems that involves optimizing the order in which read and write requests are serviced from a disk. FCFS is a simple disk scheduling algorithm that follows the principle of serving requests in the order they arrive.

2. FCFS Disk Scheduling Algorithm:

Working:

Disk requests are queued in the order they arrive.

The operating system services the requests in the order they are queued.

Advantages:

Simple and easy to implement.

Fairness, as each request is served in the order it arrives.

Disadvantages:

May result in poor performance due to lack of optimization.

May lead to the "SSTF" (Shortest Seek Time First) problem.

3. Example Scenario:

Consider disk requests for sectors 30, 25, 35, 20, and 40, and the disk head initially positioned at sector 30.

FCFS:

Queue: 30 → 25 → 35 → 20 → 40

Initial position: 30

Service order: 30 → 25 → 35 → 20 → 40

4. Conclusion:

FCFS is a straightforward disk scheduling algorithm that follows a first-come-first-serve approach. While it is easy to implement and ensures fairness in servicing requests, it may lead to suboptimal performance, especially when there are significant variations in seek times.

Notes From The Slides:



FCFS

Illustration shows total head movement of 640 cylinders