C Program For First Come First Serve (FCFS) disk scheduling algorithm

Introduction to First Come First Serve (FCFS) disk scheduling :

The simplest form of disk scheduling is, of course, the ﬁrst-come, ﬁrst-served (FCFS) algorithm. This algorithm is intrinsically fair, but it generally does not provide the fastest service. Consider, for example, a disk queue with requests for I/O to blocks on cylinders 98, 183, 37, 122, 14, 124, 65, 67. If the disk head is initially at cylinder 53, it will ﬁrst move from 53 to 98, then to 183, 37, 122, 14, 124, 65, and ﬁnally to 67, for a total head movement of 640 cylinders.

C program for First Come First Serve (FCFS) disk scheduling algorithm

#include <stdio.h>

#include <math.h>

int main()

{

    int queue[20], n, head, i, j, k, seek = 0, max, diff;

    float avg;

    printf("Enter the max range of disk\n");

    scanf("%d", &max);

    printf("Enter the size of queue request\n");

    scanf("%d", &n);

    printf("Enter the queue of disk positions to be read\n");

    for (i = 1; i <= n; i++)

        scanf("%d", &queue[i]);

    printf("Enter the initial head position\n");

    scanf("%d", &head);

    queue[0] = head;

    for (j = 0; j <= n - 1; j++)

    {

        diff = abs(queue[j + 1] - queue[j]);

        seek += diff;

        printf("Disk head moves from %d to %d with seek %d\n", queue[j], 
        queue[j + 1], diff);
    }

    printf("Total seek time is %d\n", seek);

    avg = seek / (float)n;

    printf("Average seek time is %f\n", avg);

    return 0;
}