C-Program of SSTF (Short seek time first )Disk scheduling Algorithms in operating system (OS).

  What is SSTF disk scheduling:-

                                                        Shortest seek time first (SSTF) algorithm selects the disk I/O request which requires the least disk arm movement from its current position regardless of the direction. It reduces the total seek time as compared to FCFS.

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.

Advantage:-

1. seek time reduces as compaired to the FCFS
2. Less waiting time and response time 
3. Increase throughput.

Disadvantage:-

1. starvation occurred

  C      C++      Python  

#include<stdio.h>

#include<stdlib.h>

int main()

{

int RQ[100],i,n,TotalHeadMoment=0,initial,count=0;

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);

// logic for sstf disk scheduling

/* loop will execute until all process is completed*/

while(count!=n)

{

int min=1000,d,index;

for(i=0;i<n;i++)

{

d=abs(RQ[i]-initial);

if(min>d)

{

min=d;

index=i;

}

}

TotalHeadMoment=TotalHeadMoment+min;

initial=RQ[index];

// 1000 is for max

// you can use any number

RQ[index]=1000;

count++;

}

printf("Total head movement is %d",TotalHeadMoment);

return 0;

}

Output:-

Enter the number of Request

8

Enter Request Sequence

95 180 34 119 11 123 62 64

Enter initial head Position

50

Total head movement is 236

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