Paging Flashcards
What makes paging different from segmentation?
Instead of splitting memory into variable sized chunks, we have fixed size pieces which are allocated out.
What is the difference between a page and a page frame?
The virtual address space is divided up into pages, and these pages are placed in page frames in physical memory. The page frames which the pages are placed into do not necessarily have to be next to one another.
What is the page table for?
The page table keeps track of address translations for each virtual page in a given address space. They let us know how to translate from a virtual page to a physical page frame.
How might you translate between a virtual page and a physical page frame?
In the virtual address, the first few bits may indicate which virtual page we are dealing with. The remaining bits are an offset. We can use the page table to change the first few bits from the virtual page number to the physical page frame number. The offset remains the same.
What is the valid bit on a page table?
A valid bit, to indicate if a translation is valid.
What are the protection bits on a page table?
Protection bits, to indicate a page’s protection level.
What is the present bit on a page table?
A present bit, to show if a page is in physical memory or the disk.
What is the dirty bit on a page table?
A dirty bit, to indicate if a page has been modified since last called.
What is the reference bit on a page table?
A reference bit to track if a page has been accessed.
What is the most important field on a page table entry?
The translation itself, so the corresponding physical frame number.
