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C-Program of C- Look Disk scheduling Algorithms in operating system (OS).

Rajnish Tripathi 17:44

  What is C- Look disk scheduling:-

                                                                 As LOOK is similar to SCAN algorithm, in similar way, CLOOK is similar to CSCAN disk scheduling algorithm. In CLOOK, the disk arm in spite of going to the end goes only to the last request to be serviced in front of the head and then from there goes to the other end’s last request. Thus, it also prevents the extra delay which occurred due to unnecessary traversal to the end of the disk. 

 Example:- 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.Head movement is towards low values.



Advantage:-
  1. Starvation is avoided in C-LOOK.
  2. Low variance is provided in waiting time and response time.

    Disadvantage:-

    1. An overhead to find the end request.

    Code:-

    #include<stdio.h>
    #include<stdlib.h>
    int main()
    {
    int RQ[100],i,j,n,TotalHeadMoment=0,initial,size,move;
    printf("Enter the number of Requests\n");
    scanf("%d",&n);
    printf("Enter the Requests sequence\n");
    for(i=0;i<n;i++)
    scanf("%d",&RQ[i]);
    printf("Enter initial head position\n");
    scanf("%d",&initial);
    printf("Enter total disk size\n");
    scanf("%d",&size);
    printf("Enter the head movement direction for high 1 and for low 0\n");
    scanf("%d",&move);
    // logic for C-look disk scheduling
    /*logic for sort the request array */
    for(i=0;i<n;i++)
    {
    for( j=0;j<n-i-1;j++)
    {
    if(RQ[j]>RQ[j+1])
    {
    int temp;
    temp=RQ[j];
    RQ[j]=RQ[j+1];
    RQ[j+1]=temp;
    }

    }
    }

    int index;
    for(i=0;i<n;i++)
    {
    if(initial<RQ[i])
    {
    index=i;
    break;
    }
    }
    // if movement is towards high value
    if(move==1)
    {
    for(i=index;i<n;i++)
    {
    TotalHeadMoment=TotalHeadMoment+abs(RQ[i]-initial);
    initial=RQ[i];
    }
    for( i=0;i<index;i++)
    {
    TotalHeadMoment=TotalHeadMoment+abs(RQ[i]-initial);
    initial=RQ[i];
    }
    }
    // if movement is towards low value
    else
    {
    for(i=index-1;i>=0;i--)
    {
    TotalHeadMoment=TotalHeadMoment+abs(RQ[i]-initial);
    initial=RQ[i];
    }
    for(i=n-1;i>=index;i--)
    {
    TotalHeadMoment=TotalHeadMoment+abs(RQ[i]-initial);
    initial=RQ[i];
    }
    }
    printf("Total head movement is %d",TotalHeadMoment);
    return 0;
    }

    Output:-


    Enter the number of Request
    8
    Enter the Requests Sequence
    95 180 34 119 11 123 62 64
    Enter initial head position
    50
    Enter the head movement direction for high 1 and for low 0
    1
    Total head movement is 322

    Must visit:-

                            Program of disk scheduling algorithm



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