BTCOL406 Operating Systems
Gramin Technical and Management campus Nanded
Department of computer Engineering (Degree)
Name- Atharva Yashwantrao Bodhankar PRN No: 24025081245505
Subject - BTCOL406 _Operating Systems
DOP – ___/___/ 2025 DOC – ___/___/ 2025
Practical No. 5
Aim - Implementation of various page replacement algorithms (FIFO,
Optimal, LRU).
1. FIFO Page Replacement.
Code –
#include <stdio.h>
int main() {
int frames, pages[50], temp[50], n, i, j, k, pageFaults = 0, position = 0, flag;
printf("Enter number of pages: ");
scanf("%d", &n);
printf("Enter the page reference string:\n");
for (i = 0; i < n; i++) {
scanf("%d", &pages[i]);
}
printf("Enter number of frames: ");
scanf("%d", &frames);
for (i = 0; i < frames; i++) {
temp[i] = -1; // Initialize frames as empty
}
printf("\nPage\tFrames\n");
for (i = 0; i < n; i++) {
flag = 0;
// Check if page is already in frame
for (j = 0; j < frames; j++) {
if (temp[j] == pages[i]) {
flag = 1;
break;
}
}
if (!flag) {
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temp[position] = pages[i]; // Replace the oldest page (FIFO)
position = (position + 1) % frames;
pageFaults++;
// Print current frame status
printf("%d\t", pages[i]);
for (k = 0; k < frames; k++) {
if (temp[k] != -1)
printf("%d ", temp[k]);
else
printf("- ");
}
printf("\n");
}
}
printf("\nTotal Page Faults = %d\n", pageFaults);
return 0;
}
Output –
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BTCOL406 Operating Systems
2. LRU Page Replacement
Code –
#include <stdio.h>
int main() {
int frames, pages[50], temp[50], counter[50];
int n, i, j, k, pageFaults = 0, pos, max, flag, time = 0;
printf("Enter number of pages: ");
scanf("%d", &n);
printf("Enter the page reference string:\n");
for (i = 0; i < n; i++) {
scanf("%d", &pages[i]);
}
printf("Enter number of frames: ");
scanf("%d", &frames);
for (i = 0; i < frames; i++) {
temp[i] = -1;
counter[i] = 0;
}
printf("\nPage\tFrames\n");
for (i = 0; i < n; i++) {
flag = 0;
for (j = 0; j < frames; j++) {
if (temp[j] == pages[i]) {
time++;
counter[j] = time; // Update recent use
flag = 1;
break;
}
}
if (!flag) {
// Find empty slot
for (j = 0; j < frames; j++) {
if (temp[j] == -1) {
time++;
temp[j] = pages[i];
counter[j] = time;
pageFaults++;
flag = 2;
break;
}
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BTCOL406 Operating Systems
}
}
// If no empty slot, use LRU replacement
if (flag == 0) {
int min = counter[0];
pos = 0;
for (j = 1; j < frames; j++) {
if (counter[j] < min) {
min = counter[j];
pos = j;
}
}
time++;
temp[pos] = pages[i];
counter[pos] = time;
pageFaults++;
}
if (flag != 1) {
printf("%d\t", pages[i]);
for (k = 0; k < frames; k++) {
if (temp[k] != -1)
printf("%d ", temp[k]);
else
printf("- ");
}
printf("\n");
}
}
printf("\nTotal Page Faults = %d\n", pageFaults);
return 0;
}
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BTCOL406 Operating Systems
Output –
3. Optimal Page Replacement
Code –
#include <stdio.h>
int predict(int pages[], int temp[], int n, int index, int frames) {
int res = -1, farthest = index;
for (int i = 0; i < frames; i++) {
int j;
for (j = index; j < n; j++) {
if (temp[i] == pages[j]) {
if (j > farthest) {
farthest = j;
res = i;
}
break;
}
}
// If page not found in future
if (j == n)
return i;
}
return (res == -1) ? 0 : res;
}
int main() {
int frames, pages[50], temp[50];
int n, i, j, pageFaults = 0, hit;
printf("Enter number of pages: ");
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BTCOL406 Operating Systems
scanf("%d", &n);
printf("Enter the page reference string:\n");
for (i = 0; i < n; i++) {
scanf("%d", &pages[i]);
}
printf("Enter number of frames: ");
scanf("%d", &frames);
for (i = 0; i < frames; i++)
temp[i] = -1;
printf("\nPage\tFrames\n");
for (i = 0; i < n; i++) {
hit = 0;
// Page hit check
for (j = 0; j < frames; j++) {
if (temp[j] == pages[i]) {
hit = 1;
break;
}
}
if (!hit) {
int empty = -1;
// Check for empty frame
for (j = 0; j < frames; j++) {
if (temp[j] == -1) {
empty = j;
break;
}
}
if (empty != -1) {
temp[empty] = pages[i];
} else {
int pos = predict(pages, temp, n, i + 1, frames);
temp[pos] = pages[i];
}
pageFaults++;
printf("%d\t", pages[i]);
for (j = 0; j < frames; j++) {
if (temp[j] != -1)
printf("%d ", temp[j]);
else
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printf("- ");
}
printf("\n");
}
}
printf("\nTotal Page Faults = %d\n", pageFaults);
return 0;
}
Output –
Practical N0. 4 Page 7 of 7
