Experiment No.
10
File Management & I/O Management
A. Implement disk scheduling algorithms FCFS, SSTF.
Name Of Student:-Bhagyashri Kaleni Sutar
Roll No:-75
Date of Performance:02/04/2025
Date of Submission: 09/04/2025
Marks:
Sign:
Experiment No. 10
Aim: To study and implement disk scheduling algorithms FCFS.
Objective:
The main purpose of disk scheduling algorithm is to select a disk request from the
queue of IO requests and decide the schedule when this request will be processed.
Theory:
TYPES OF DISK SCHEDULING ALGORITHMS
Although there are other algorithms that reduce the seek time of all requests, I
will only concentrate on the following disk scheduling algorithms:
⦁ First Come-First Serve (FCFS)
⦁ Shortest Seek Time First (SSTF)
⦁ Elevator (SCAN)
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⦁ Circular SCAN (C-SCAN)
⦁ C-LOOK
Given the following queue -- 95, 180, 34, 119, 11, 123, 62, 64 with the Read-write
head initially at the track 50 and the tail track being at 199 let us now discuss the
different algorithms.
FCFS
First Come -First Serve (FCFS)
All incoming requests are placed at the end of the queue. Whatever number
that is next in the queue will be the next number served. Using this algorithm
doesn't provide the best results. To determine the number of head movements
you would simply find the number of tracks it took to move from one
request to the next. For this case it
went from 50 to 95 to 180 and so on. From 50 to 95 it moved 45 tracks. If you
tally up the total number of tracks you will find how many tracks it had to go
through before finishing the entire request. In this example, it had a total head
movement of 640 tracks. The disadvantage of this algorithm is noted by the
oscillation from track 50 to track 180 and then back to track 11 to 123 then to
64. As you will soon see, this is the worse algorithm that one can use.
Program:
import java.util.Arrays;
public class DiskScheduling {
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public static void fcfs(int[] requests, int
head) { int totalSeekTime = 0;
int currentHead = head;
System.out.println("FCFS Disk Scheduling:");
System.out.print("Sequence: " + head);
for (int request : requests) {
totalSeekTime += Math.abs(currentHead - request);
currentHead = request;
System.out.print(" -> " + request);
System.out.println("\nTotal Seek Time: " + totalSeekTime);
public static void sstf(int[] requests, int head) {
int
totalSeekTime =
0; int
currentHead =
head;
int[] remainingRequests = requests.clone();
boolean[] visited = new boolean[remainingRequests.length];
System.out.println("SSTF Disk Scheduling:");
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System.out.print("Sequence: " + head);
for (int i = 0; i < remainingRequests.length;
i++) { int shortestSeek =
Integer.MAX_VALUE;
int shortestIndex = -1;
for (int j = 0; j
< remainingRequests.length; j++) { if (!
visited[j]) {
int seek = Math.abs(currentHead -
remainingRequests[j]); if (seek < shortestSeek) {
shortestSeek = seek;
shortestIndex = j;
}
totalSeekTime += shortestSeek;
currentHead = remainingRequests[shortestIndex];
visited[shortestIndex] = true;
System.out.print(" -> " + currentHead);
System.out.println("\nTotal Seek Time: " + totalSeekTime);
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public static void main(String[] args) {
int[] requests = {98, 183, 37, 122, 14, 124, 65, 67};
int head = 53;
fcfs(request
s, head);
sstf(request
s, head);
//output
FCFS Disk Scheduling:
Sequence: 53 -> 98 -> 183 -> 37 -> 122 -> 14 -> 124 -> 65 -> 67
Total Seek
Time: 640 SSTF
Disk Scheduling:
Sequence: 53 -> 65 -> 67 -> 37 -> 14 -> 98 -> 122 -> 124 -> 183
Total Seek Time: 236
Conclusion:
Why is Disk Scheduling important?
Ans:- Disk scheduling is crucial in operating systems because it significantly impacts
a computer's overall performance. Here's a breakdown of its importance:
⦁ Optimizing Disk I/O:
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⦁ Disk drives are mechanical devices, and accessing data on them is
relatively slow compared to accessing data in RAM.
⦁
⦁ Disk scheduling algorithms aim to minimize the time it takes to access
data on the disk, thereby improving the efficiency of disk input/output
(I/O) operations.
⦁ Minimizing Seek Time:
⦁ Seek time is the time it takes for the disk arm to move to the correct track.
⦁
⦁ Disk scheduling algorithms prioritize requests to reduce the distance
the disk arm has to travel, thus minimizing seek time.
⦁
⦁ Reducing Rotational Latency:
⦁ Rotational latency is the time it takes for the desired sector to rotate
under the read/write head.
⦁
⦁ Efficient scheduling can also contribute to reducing this latency.
⦁
⦁ Maximizing Throughput:
⦁ By optimizing disk access, disk scheduling algorithms increase the
number of I/O requests that can be processed in a given time, thereby
maximizing throughput.
⦁
⦁ Ensuring Fairness:
⦁ In multi-user or multi-tasking environments, disk scheduling
algorithms ensure that all processes have fair access to the disk,
preventing any one process from monopolizing the disk
resources.
⦁ Improving System Responsiveness:
⦁ Efficient disk scheduling leads to faster data retrieval, which
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improves the overall responsiveness of the computer system.
In essence, disk scheduling is about managing and optimizing the order in which disk
access requests are handled, leading to a more efficient and responsive computer system.
