II) Consider a disk queue with requests for I/O to blocks on cylinders 98, 183, 41, 122, 14, 124, 65, 67. The head is initially at cylinder number 53 moving towards larger cylinder numbers on its servicing pass. The cylinders are numbered from 0 to 199.
Write an OS program to implement SSTF Disk Scheduling algorithm to calculate the total head movement (in number of cylinders).
Solution:
#include<stdio.h>
#include<stdlib.h>
int front,rear;
void init()
{
front=rear=-1;
}
void display(int *Q)
{
int i;
printf("\nFront %d\t",front);
for(i=front;i<=rear;i++)
printf("\t%d",Q[i]);
}
void enqueu(int *Q,int n,int var)
{
if(rear==n)
printf("\nQueue is Full");
else
{
if(front==-1&&rear==-1)
{
front++;
rear++;
}
else
rear++;
Q[rear]=var;
}
}
int SSTF(int *Q,int n,int initial)
{
int min,diff,index,TotalHeadMoment=0,count=0,i;
while(count!=n)
{
min=1000;
for(i=0;i<n;i++)
{
diff=abs(Q[i]-initial);
if(min>diff)
{
min=diff;
index=i;
}
}
printf("\nIndex=%d\n",index);
printf("Disk head moves from %d to %d with seek %d\n",initial,Q[index],min);
TotalHeadMoment=TotalHeadMoment+min;
initial=Q[index];
Q[index]=1000;
count++;
}
return TotalHeadMoment;
}
int main()
{
int ReadyQueue[100],i,n,TotalHeadMoment,initial,max,var;
init();
printf("\nEnter the max range of disk\n");
scanf("%d",&max);
printf("\nEnter the size of queue request\n");
scanf("%d",&n);
printf("\nEnter the queue of disk positions to be read\n");
for(i=0;i<n;i++)
{
scanf("%d",&var);
if(var<0||var>max)
printf("\nError..!Given Position is invalid\n");
else
{
enqueu(queue,n,var);
}
}
printf("\nGiven Request Queue Is\n");
display(ReadyQueue);
printf("\nEnter the initial head position\n");
scanf("%d",&initial);
TotalHeadMoment=SSTF(ReadyQueue,n,initial);
printf("\n\nTotal head movement is %d",TotalHeadMoment);
}
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