Os Memory Management Questions
The clock page replacement algorithm, also known as the second-chance algorithm, is a memory management technique used by operating systems to select which page to replace when there is a page fault.
The process of the clock page replacement algorithm involves the following steps:
1. Maintain a circular list, called the clock hand, which represents the frames in memory.
2. Each frame in memory is associated with a reference bit, which is initially set to 0.
3. When a page fault occurs, the operating system checks the reference bit of the frame pointed by the clock hand.
4. If the reference bit is 0, indicating that the page has not been recently accessed, the page is selected for replacement.
5. The selected page is then swapped out from memory, and the new page is brought in to occupy the frame.
6. The reference bit of the newly brought-in page is set to 1.
7. The clock hand is then advanced to the next frame in the circular list.
8. If the reference bit of the frame pointed by the clock hand is 1, indicating that the page has been recently accessed, the reference bit is set to 0 and the clock hand is advanced to the next frame.
9. Steps 4 to 8 are repeated until a frame with a reference bit of 0 is found, and that page is replaced.
The clock page replacement algorithm ensures that pages that have been recently accessed are given a second chance before being replaced, hence the name "second-chance algorithm". This helps in reducing unnecessary page replacements and improving overall system performance.