C program for C-SCAN disk scheduling algorithm

Introduction to C-SCAN disk scheduling :

                   Circular SCAN (C-SCAN) scheduling is a variant of SCAN designed to provide a more uniform wait time. Like SCAN, C-SCAN moves the head from one end of the disk to the other, servicing requests along the way. When the head reaches the other end, however, it immediately returns to the beginning of the disk without servicing any requests on the return trip (Figure 10.7). The C-SCAN scheduling algorithm essentially treats the cylinders as a circular list that wraps around from the final cylinder to the first one.


C program for C-SCAN disk scheduling :

#include<stdio.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;

}

 OUTPUT :