Operating systems calculator
Use this page replacement algorithm calculator to solve operating-system memory management problems without drawing every frame by hand. It supports FIFO, LRU, Optimal, Clock, LFU, and LIFO, then shows page faults, hits, hit rate, miss rate, and the full frame table.
Lower page faults usually mean better performance for the same reference string and frame count.
| Algorithm | Page Faults | Hits | Hit Rate | Miss Rate |
|---|---|---|---|---|
| FIFOFirst In First Out | 10 | 3 | 23.08% | 76.92% |
| LRULeast Recently Used | 9 | 4 | 30.77% | 69.23% |
| OptimalOptimal Page Replacement | 7 | 6 | 46.15% | 53.85% |
| ClockSecond Chance / Clock | 9 | 4 | 30.77% | 69.23% |
| LFULeast Frequently Used | 8 | 5 | 38.46% | 61.54% |
| LIFOLast In First Out | 9 | 4 | 30.77% | 69.23% |
Frame state after each reference using FIFO.
| Step | Page | Frame 1 | Frame 2 | Frame 3 | Result | Evicted | Reason |
|---|---|---|---|---|---|---|---|
| 1 | 7 | 7 | - | - | Fault | - | Free frame available, so 7 is loaded without evicting another page. |
| 2 | 0 | 7 | 0 | - | Fault | - | Free frame available, so 0 is loaded without evicting another page. |
| 3 | 1 | 7 | 0 | 1 | Fault | - | Free frame available, so 1 is loaded without evicting another page. |
| 4 | 2 | 2 | 0 | 1 | Fault | 7 | 7 entered memory first, so FIFO evicts it. |
| 5 | 0 | 2 | 0 | 1 | Hit | - | 0 is already in memory, so this reference is a hit. |
| 6 | 3 | 2 | 3 | 1 | Fault | 0 | 0 entered memory first, so FIFO evicts it. |
| 7 | 0 | 2 | 3 | 0 | Fault | 1 | 1 entered memory first, so FIFO evicts it. |
| 8 | 4 | 4 | 3 | 0 | Fault | 2 | 2 entered memory first, so FIFO evicts it. |
| 9 | 2 | 4 | 2 | 0 | Fault | 3 | 3 entered memory first, so FIFO evicts it. |
| 10 | 3 | 4 | 2 | 3 | Fault | 0 | 0 entered memory first, so FIFO evicts it. |
| 11 | 0 | 0 | 2 | 3 | Fault | 4 | 4 entered memory first, so FIFO evicts it. |
| 12 | 3 | 0 | 2 | 3 | Hit | - | 3 is already in memory, so this reference is a hit. |
| 13 | 2 | 0 | 2 | 3 | Hit | - | 2 is already in memory, so this reference is a hit. |
Learn how page faults, hits, frames, and replacement rules are calculated for common OS algorithms.
FIFO evicts the oldest loaded page, LRU evicts the page that has not been used for the longest time, and Optimal evicts the page whose next use is farthest in the future. The calculator runs each rule against the same reference string so the page fault counts are easy to compare.
Each row shows the requested page, frame contents after the reference, whether it was a hit or page fault, the evicted page, and the replacement reason. That makes it easier to find exactly where a manual calculation went wrong.
The hit rate is hits divided by total references, while the miss rate is page faults divided by total references. These metrics help compare algorithms beyond just counting faults.
Many examples focus only on FIFO, LRU, and Optimal, but operating-system classes may also discuss Second Chance or Clock, Least Frequently Used, and Last In First Out. This tool includes those modes for broader practice.
Follow these steps to calculate page faults and compare page replacement algorithms.
Paste or type the sequence of page references separated by spaces, commas, or semicolons.
Set how many memory frames are available for the simulation.
Choose FIFO, LRU, Optimal, Clock, LFU, or LIFO to see the matching step-by-step calculation.
Use the comparison table to see page faults, hits, hit rate, and miss rate for every supported algorithm.
Quick answers about FIFO, LRU, Optimal, Clock, page faults, and hit rate calculations.
It is a tool that simulates how an operating system decides which memory page to evict when a new page is requested and all frames are full.
This calculator supports FIFO, LRU, Optimal, Clock or Second Chance, LFU, and LIFO.
Type page references separated by spaces, commas, or semicolons, such as 7 0 1 2 0 3 0 4.
A page fault happens when the requested page is not currently loaded in the available frames, so the algorithm must load it and may need to evict another page.
Optimal chooses the page that will be used farthest in the future, so it has perfect future knowledge. Real systems cannot normally implement it, but it is useful as a benchmark.
Yes. FIFO can show Belady's anomaly, where adding more frames causes more page faults for some reference strings.
