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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>FCFS - Disk Scheduling Algorithms</title>
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<h1>FCFS: First Come First Serve</h1>
</br>
<p>FCFS (First Come First Serve) is simplest disk scheduling algorithm. Each requests are taken/executed in the
sequence of their arrival in the disk queue. As a result, there is no starvation
in this algorithm. However, it isn't fast compared to other algorithms.</p>
</br>
<h3> Advantages:</h3>
<ul>
<li>
There is no starvation in FCFS.
</li>
<li>
FCFS is simple and straight forward approach which means there are no indefinite delays.
</li>
<li>
In FCFS, fair chance given to each request.
</li>
</ul>
</br>
<h3> Disadvantages:</h3>
<ul>
<li>
FCFS isn't considered an efficient and optimized approach.
</li>
<li>
FCFS can be time consuming.
</li>
</ul>
<h3> Example: </h3>
<ul>
<li>
Suppose a disk contains 200 tracks (0-199) and the request queue contains track no: 176, 79, 34, 60, 92, 11,
41,
114.
</li>
<li>
The current position of the read/write head is 50. Now we have to calculate the total number of track
movements
of read/write head using FCFS scheduling.
</li>
<li>
As mentioned in the following example, the disk contains 200 tracks, so we take a track line between 0 to 199.
</li>
<li>
The current position of the read/write head is 50. So, we start from 50, then move read/write head in the FCFS
order. When all the requests are addressed, then we calculate a total number of cylinders moved by the head.
</li>
<br>
<img src="images/fcfs-eg-graph.jpg" alt="graph of example">
<br> <br>
<li>
Total Number of cylinders moved by the head =
(176-50)+(176-79)+(79-34)+(60-34)+(92-60)+(92-11)+(41-11)+(114-41)
= 510
</li>
</ul>
<h3>Steps to Implement Algorithm:</h3>
<ol>
<li>
Let Request array represents an array storing indexes of tracks that have been requested in ascending order of
their time of arrival. 'head' is the position of disk head.
</li>
<li>
Let us one by one take the tracks in default order and calculate the absolute distance of the track from the
head.
</li>
<li>
Increment the total seek count with this distance.
</li>
<li>
Currently serviced track position now becomes the new head position.
</li>
<li>
Go to step 2 until all tracks in request array have not been serviced.
</li>
</ol>
<p>
<b> Time Complexity: O ( N )   Auxiliary Space: O ( N ) </b>
</p>
<a class="simulate" href="FCFS/fcfs.html">Simulate</a>
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<h3>About</h3>
<p>
This project was done by Team 2 Group 5 as a part of Operating
Systems Lab.
</p>
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