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:

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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Arogya Thapa Magar

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