OS C Scan Disk Scheduling Algorithm

Operating Systems Lab Manual / OS C Scan Disk Scheduling Algorithm

Program Name	Write a C Program for C Scan disk scheduling in operating systems
Theory	Circular SCAN (C-SCAN) scheduling algorithm is a modified version of SCAN disk scheduling algorithm but it serve the requests more uniformly. Like SCAN / Elevator Algorithm, C-SCAN moves the head from one end servicing all the requests to the other end. In C Scan the Head starts from one end of the disk and move towards the other end servicing all the requests in between. After reaching end, the head reverses its direction.It then returns to the starting end without servicing any request in between and starts serving the requests.
Program	#include<stdio.h> #include<stdlib.h> void main() { int requests[100],i,j,n,TotalHeadMoments=0,initial,size,move, index; printf("Enter Number of Requests:"); scanf("%d",&n); printf("\nEnter Requests sequence:"); for(i=0;i<n;i++) scanf("%d",&requests[i]); printf("\nEnter Initial Head Positions:"); scanf("%d",&initial); printf("\nEnter Total Disk size:"); scanf("%d",&size); printf("Enter Head Movements Directions(high = 1 and low = 0):"); scanf("%d",&move); // Scan disk scheduling logic /logic for sort the request array / for(i=0;i<n;i++) for( j=0;j<n-i-1;j++) if(requests[j]>requests[j+1]) { int temp; temp=requests[j]; requests[j]=requests[j+1]; requests[j+1]=temp; } for(i=0;i<n;i++) if(initial<requests[i]) { index=i; break; } // if movement is towards high value if(move==1) { for(i=index;i<n;i++) { TotalHeadMoments=TotalHeadMoments+abs(requests[i]-initial); initial=requests[i]; } // last movement for max size TotalHeadMoments=TotalHeadMoments+abs(size-requests[i-1]-1); /movement max to min disk / TotalHeadMoments=TotalHeadMoments+abs(size-1-0); initial=0; for( i=0;i<index;i++) { TotalHeadMoments=TotalHeadMoments+abs(requests[i]-initial); initial=requests[i]; } } // if movement is towards low value else { for(i=index-1;i>=0;i--) { TotalHeadMoments=TotalHeadMoments+abs(requests[i]-initial); initial=requests[i]; } // last movement for min size TotalHeadMoments=TotalHeadMoments+abs(requests[i+1]-0); /movement min to max disk / TotalHeadMoments=TotalHeadMoments+abs(size-1-0); initial =size-1; for(i=n-1;i>=index;i--) { TotalHeadMoments=TotalHeadMoments+abs(requests[i]-initial); initial=requests[i]; } } printf("Total head movement is %d",TotalHeadMoments); }
Input	Enter Number of Requests:8 Enter Requests sequence:95 180 34 119 11 123 62 64 Enter Initial Head Positions:50 Enter Total Disk size:200 Enter Head Movements Directions(high = 1 and low = 0):1
Output	Total head movement is 382

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