Os Memory Management Questions Medium
The WS-CLOCK (Working Set Clock) page replacement algorithm is a variation of the CLOCK algorithm used in memory management. It aims to improve the efficiency of page replacement by considering the working set of a process.
The working set of a process refers to the set of pages that are actively being used by the process at a given time. The WS-CLOCK algorithm keeps track of the working set of each process and makes page replacement decisions based on this information.
Here is a step-by-step description of how the WS-CLOCK algorithm works:
1. Each page in the memory is associated with a reference bit, which is initially set to 0. Additionally, a clock hand is maintained to keep track of the current position in the memory.
2. When a page fault occurs, indicating that a requested page is not present in the memory, the algorithm starts searching for a suitable page to replace.
3. The clock hand starts at the current position and begins scanning the memory in a circular manner.
4. For each page encountered, the algorithm checks its reference bit. If the reference bit is 0, it means the page has not been recently accessed and can be a candidate for replacement.
5. If the reference bit is 1, it means the page has been recently accessed. In this case, the algorithm clears the reference bit and moves to the next page.
6. The clock hand continues scanning until it finds a page with a reference bit of 0. This page is selected for replacement.
7. Before replacing the selected page, the algorithm checks if it belongs to the working set of any process. If it does, the page is skipped, and the clock hand moves to the next page.
8. If the selected page does not belong to any working set, it is replaced with the new page requested by the process experiencing the page fault.
9. The clock hand is then advanced to the next page, and the process continues from step 4 for the next page replacement.
By considering the working set of each process, the WS-CLOCK algorithm aims to prioritize pages that are actively being used, reducing the number of unnecessary page replacements and improving overall system performance.