First Come First Serve

 

In my previous publish titled “Disk Scheduling”, I tried to provide an explanation for approximately the fundamentals of disk scheduling.

In this & upcoming posts, we will look a number of the extensively used disk preparation algorithms.

In this pole, I will start with the most easy and normally used disk scheduling algorithm called fcfs.

  First Come First Serve (FCFS)

This is the most effective shape of preparation.

It is similar the FIFO CPU scheduling set of rules.

According to FCFS algorithm, all requests might be serviced inside the equal order wherein they come.

In other words, request will be serviced within the sequential manner.

It does not offer the fastest get entry to and it is also now not most fulfilling.

It has higher are trying to find time examine to other algorithms.

For instance, A disk queue with request of input, output of two blocks on cylinders are as ninety eight, 183, 37, 122, 14, 124, 65, 67.

If disk head is first of all at cylinder fifty three than it's going to move from 53 to ninety eight this is the give up of the request of the block and to 183, 37 and so forth.

We can see overall head actions and cylinders to be traveled since the request servicing queue.

If the request for rolls is 37 and 14 to be serviced collectively earlier than or after the demand at 122 and 124, the overall head motion will be decreased and overall performance could be advanced.

FCFS Overview

The First Come First Serve (FCFS) disk scheduling algorithm mirrors the simplicity of the FIFO (First In, First Out) CPU scheduling approach. Under FCFS, incoming disk requests are serviced in the exact sequence they arrive, akin to a queue. This straightforward methodology might seem intuitive, but it comes with inherent drawbacks. Notably, FCFS fails to provide optimal access times and can result in higher seek times compared to more sophisticated algorithms.

Working Mechanism

To comprehend the FCFS algorithm's functionality, consider a disk queue with requests for input and output of two blocks on cylinders: 98, 183, 37, 122, 14, 124, 65, and 67. Assuming the disk head initiates its movement from cylinder 53, FCFS dictates that it progresses sequentially through the requests. Therefore, the disk head moves from 53 to 98, followed by 183, 37, and so forth. This sequential processing might not be the most efficient, as it often involves unnecessary travel across cylinders, leading to increased seek times.

Illustrative Example

To illustrate the shortcomings of FCFS, let's consider a scenario where requests for cylinders 37 and 14 could be serviced consecutively before or after the demands at 122 and 124. By rearranging the order in which these requests are fulfilled, the overall head movement and cylinder traversal can be minimized. This optimization can enhance performance by reducing the total seek time, a crucial factor in disk scheduling efficiency.

Conclusion and Future Discussions

In conclusion, the First Come First Serve (FCFS) disk scheduling algorithm, while straightforward, falls short of providing the fastest access times. Future articles in this series will explore more advanced disk scheduling algorithms that aim to address the limitations of FCFS, offering improved performance in terms of seek times and overall system efficiency. Stay tuned for an in-depth exploration of these algorithms in upcoming posts.