FIFO page replacement algorithm in C

FIFO page replacement algorithm in C with output of program

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The operating system uses the method of paging for memory management. This method involves various algorithms known as page replacements algorithms that decide which page should be replaced by a new one on demand. A demand is made when the operating system needs a page for processing which is not contained in the main memory. Such situations are termed as page faults.

At such times, a page from secondary memory is replaced with the existing page from the main memory. The method used here is FIFO , First In First Out . This method is one of the simplest methods in which the operating system maintains all the pages in a queue. The oldest pages are kept in the front and the latest ones at the back. When a page fault occurs, the oldest pages are removed first and the latest ones are added.

Let’s see how the algorithm works. The steps are as follows:

FIFO page replacement algorithm (Working)

  • Start the process and traverse through the pages.
  • Declare the size with respect to the page length
  • Check if there’s a need for replacement of a page from memory.
  • Check the need of replacement from old page to new page in memory
  • Form a queue to hold all pages
  • Insert the page require memory into the queue
  • Check for bad replacement and page fault
  • Get the number of processes to be inserted
  • Display the values
  • End the process

Hope the algorithm was clear. Let’s get into the coding part now.

FIFO page replacement program in C

#include<stdio.h>
int main()
{
int i,j,n,a[50],frame[10],no,k,avail,count=0;
            printf("\n ENTER THE NUMBER OF PAGES:\n");
scanf("%d",&n);
            printf("\n ENTER THE PAGE NUMBER :\n");
            for(i=1;i<=n;i++)
            scanf("%d",&a[i]);
            printf("\n ENTER THE NUMBER OF FRAMES :");
            scanf("%d",&no);
for(i=0;i<no;i++)
            frame[i]= -1;
                        j=0;
                        printf("\tref string\t page frames\n");
for(i=1;i<=n;i++)
                        {
                                    printf("%d\t\t",a[i]);
                                    avail=0;
                                    for(k=0;k<no;k++)
if(frame[k]==a[i])
                                                avail=1;
                                    if (avail==0)
                                    {
                                                frame[j]=a[i];
                                                j=(j+1)%no;
                                                count++;
                                                for(k=0;k<no;k++)
                                                printf("%d\t",frame[k]);
}
                                    printf("\n");
}
                        printf("Page Fault Is %d",count);
                        return 0;
}

Output of Program

 
ENTER THE NUMBER OF PAGES:  20
ENTER THE PAGE NUMBER :       7 0 1 2 0 3 0 4 2 3 0 3 2 1 2 0 1 7 0 1
ENTER THE NUMBER OF FRAMES :3
      ref string       page frames
7               7       -1      -1
0               7       0       -1
1               7       0       1
2               2       0       1
0
3               2       3       1
0               2       3       0
4               4       3       0
2               4       2       0
3               4       2       3
0               0       2       3
3
2
1               0       1       3
2               0       1       2
0
1
7               7       1       2
0               7       0       2
1               7       0       1
Page Fault Is 15

Hope you learnt something useful from the tutorial.

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