C Program FIFO Page Replacement Policy : Explanation

Program : [ Click Here ]

Step 1 : Accept Given Data .

  1. Frame Number  : fno
  2. Number of Pages  : count
  3. Actual Pages : arr[100] 
void accept()
{
int i;
printf("nEnter the number of Frames : ");
scanf("%d",&fno);

printf("nEnter the number of Pages : ");
scanf("%d",&count);

printf("nEnter the Page No : ");
for(i=0;i< count;i++)
    scanf("%d",&arr[i]);
}




Step 2 :


    

  1. Now we have Pages and Frame Size.
    2. 

  2.  Total Number of Pages is Given by Variable : “Count“.
    3. 



Logic :


    

  • Now We are Creating Circular Linked List Whose Size is equal to “Frame Size“
    • 

  • Initialize Each Node’s Data = -99.
    • 

  • -99 Tells us That Place is Empty
    • 

  • Call Create Function. 
    • 



Size of Linked List = Frame Size




Step 3 :


    

  • After Creating Initial Setup Call Function : fifo().
    • 

  • While Inserting Element in Frame [i.e in Linked List ] We have to Check Whether -
    • 

      

    • Page number is Already Present or Not.
      • 

    • There is Empty Location or not.
      • 

    



temp = start;  //Temporary Purpose
last = start;  //Replacement Purpose
curr = start;  //Current Purpose ->-99


We have To insert Total Number of Pages = “Value Specified in Count” so we requires 1 for loop.


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


    

  • Check Whether First Page is already Present or not.
    • 



res = search(arr[i]);


    

  • If Page is Present then Don’t Take any Action , and Read Next Page.
    • 

  • But If Page is Present then we have to insert Page in Linked List 
    • 



Step 4 :


if(res == 0)
     {
     fault++;
     if(curr->data == -99)
        {
        curr->data = arr[i];
        curr = curr->next;
        }
     else
        {
        last ->data = arr[i];
        last = last->next;
        }
     }//end outer if


    

  • If Linked List have Blank Space then First “If Part” gets Executed.
    • 

  • If Linked List doesn’t have Blank Space then Overwrite on the Oldest Node. [ “last”  is used for Keeping Track of Oldest Node , After Overwriting Move “last” one position ahead. ]
    •