PPT Slide
Clock Page Replacement Algorithms
- Hopefully the hardware not only supports the ref bit, but also a modified or dirty bit - a bit that is set indicating a value has been written somewhere inside of the page frame (a memory write occurred).
- This gives us two bits we can use to “sort” the page references. A page with a dirty bit set is, in general, more expensive to handle (the page has to be written out to the swap device before a new page can be read into the page frame) -- it will take twice as long to process.
- We can modify the basic clock algorithm to take the ref bit and dirty bit into account (Figure 12.7).