Os Memory Management Questions Medium
The OPT (Optimal) page replacement algorithm is an optimal algorithm used in memory management to determine which page to replace when a page fault occurs. It is based on the principle of selecting the page that will not be used for the longest period of time in the future.
The working of the OPT page replacement algorithm involves the following steps:
1. When a page fault occurs, the operating system checks if there is an empty frame in the main memory. If there is an empty frame, the page is simply loaded into that frame.
2. If there are no empty frames available, the operating system needs to select a page to replace. The OPT algorithm selects the page that will not be used for the longest period of time in the future.
3. To determine the page that will not be used for the longest period of time, the OPT algorithm requires knowledge of the future memory references. However, since it is not possible to predict the future memory references accurately, the OPT algorithm uses a theoretical approach.
4. The OPT algorithm assumes that it has perfect knowledge of the future memory references and selects the page that will be referenced furthest in the future. It scans the remaining memory references and selects the page that will be referenced last.
5. Once the page to be replaced is determined, the operating system swaps it out from the main memory and loads the new page into the freed frame.
6. The OPT algorithm repeats this process for each page fault, always selecting the page that will not be used for the longest period of time.
The OPT page replacement algorithm is considered optimal because it guarantees the lowest possible page fault rate. However, it is not practical to implement in real-time systems as it requires knowledge of future memory references, which is not feasible. It is often used as a benchmark to evaluate the performance of other page replacement algorithms.