Disk Scheduling: Understanding FCFS, SSTF, SCAN & C-SCAN |…

What Are Disk Scheduling Algorithms?

Disk scheduling is a crucial aspect of managing the read/write head's movement on a hard-disk drive. These algorithms determine the order in which requests are serviced, optimizing seek times and overall performance.

The four main disk scheduling algorithms—First-Come-First-Served (FCFS), Shortest Seek Time First (SSTF), SCAN, and C-SCAN—are designed to handle varying workloads efficiently.

How Do These Algorithms Work?

In FCFS, requests are serviced in the order they arrive. This is simple but can lead to inefficiencies if requests are not well-ordered.

SSTF prioritizes servicing the closest request first, which can reduce seek times but may cause starvation of distant requests.

live demo · related simulation● LIVE

SCAN and C-SCAN Algorithms

The SCAN algorithm moves the head from one end to another, servicing all requests in a single direction. If no request is found, it reverses direction.

C-SCAN (Circular SCAN) operates similarly but wraps around to the start after reaching the end, ensuring continuous service.

Why Do These Algorithms Matter?

Efficient disk scheduling can significantly impact system performance and user experience. By reducing seek times and optimizing data access, these algorithms enhance overall system responsiveness.

Understanding these algorithms helps in designing better storage systems and improving the performance of hard disk drives.

Frequently asked questions

What is the main difference between FCFS and SSTF?

FCFS schedules requests based on their arrival order, while SSTF prioritizes servicing the closest request first to minimize seek times.

How does SCAN differ from C-SCAN in disk scheduling?

SCAN moves the head from one end of the disk to another and then reverses direction if no requests are found. C-SCAN wraps around to the start after reaching the end, ensuring continuous service.

Why is SSTF considered less fair than other algorithms?

SSTF can lead to starvation of distant requests since it only services the closest request at each step, potentially leaving far-off requests unattended for long periods.

What are the advantages and disadvantages of using C-SCAN over SCAN?

C-SCAN ensures continuous service by wrapping around, which can improve overall performance. However, it may not be as efficient in terms of seek times compared to SCAN when requests are well-ordered.

Try it live

Everything above runs in your browser — open Disk Scheduling: FCFS, SSTF, SCAN & C-SCAN and change the parameters while it is running. Nothing is installed, nothing is uploaded, the whole model lives in one tab.

▶ Open Disk Scheduling: FCFS, SSTF, SCAN & C-SCAN simulation