C Program for C-SCAN Disk Scheduling Algorithm | C Programming

Introduction to C-SCAN disk scheduling :

                   Circular SCAN (C-SCAN) scheduling is a variant of SCAN designed to provide a more uniform wait time. Circular-SCAN The algorithm is an improved version of the SCAN Algorithm.

Different Types of Disk Scheduling Algorithm:

Here are some steps followed to use C-SCAN Algorithm: -

• Like SCAN, C-SCAN moves the head from one end of the disk to the other, servicing requests along the way.
• After reaching the other end, the head reverses its direction. 
• It then returns to the starting end without servicing any request in between.
• This process repeats time and again until the scanning is completed.

The C-SCAN scheduling algorithm essentially Treats the cylinders as a circular list that wraps around from the final cylinder to the first one.

Here are Some Advantages:-

• The waiting time for the cylinders just visited by the head is reduced as compared to the SCAN Algorithm.
• It provides uniform waiting time and better response time.

Here are Some Disadvantages:-

• It causes more seek movements as compared to SCAN Algorithm.
• It causes the head to move till the end of the disk even if there are no requests to be serviced.

Also Read: Disk Scheduling For Shortest Seek Time First (SSTF)

C Program for C-SCAN Disk Scheduling Algorithm

#include <stdio.h>
#include <math.h>
int main()
{
    int queue[20], n, head, i, j, k, seek = 0, max, diff, temp, queue1[20],
    queue2[20], temp1 = 0, temp2 = 0;
    float avg;
    printf("Enter the max range of disk\n");
    scanf("%d", &max);
    printf("Enter the initial head position\n");
    scanf("%d", &head);
    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", &temp);
        if (temp >= head)
        {
            queue1[temp1] = temp;
            temp1++;
        }
        else
        {
            queue2[temp2] = temp;
            temp2++;
        }
    }
    for (i = 0; i < temp1 - 1; i++)
    {
        for (j = i + 1; j < temp1; j++)
        {
            if (queue1[i] > queue1[j])
            {
                temp = queue1[i];
                queue1[i] = queue1[j];
                queue1[j] = temp;
            }
        }
    }
    for (i = 0; i < temp2 - 1; i++)
    {
        for (j = i + 1; j < temp2; j++)
        {
            if (queue2[i] > queue2[j])
            {
                temp = queue2[i];
                queue2[i] = queue2[j];
                queue2[j] = temp;
            }
        }
    }
    for (i = 1, j = 0; j < temp1; i++, j++)
        queue[i] = queue1[j];
    queue[i] = max;
    queue[i + 1] = 0;
    for (i = temp1 + 3, j = 0; j < temp2; i++, j++)
        queue[i] = queue2[j];
    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;
}

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