OS Scan / Elevator Disk Scheduling Algorithm

Operating Systems Lab Manual / OS Scan / Elevator Disk Scheduling Algorithm

Program Name	Write a C Program for Scan/ Elevator disk scheduling in operating systems
Theory	In Scan / Elevator Algorithm, the disk arm moves into a particular direction till the end, completing all the requests coming in its way, and then it turns backend moves in the reverse direction completing requests coming in its way.
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 //Sort the request array logic 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; } // movement 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); initial = size-1; for(i=index-1;i>=0;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); initial =0; for(i=index;i<n;i++) { TotalHeadMoments=TotalHeadMoments+abs(requests[i]-initial); initial=requests[i]; } } printf("Total Head Movements: %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 Movements: 337

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