Question

I am reading up on paging and memory management unit on wikipedia. How does reference and modified bit of the page table entry affects the operation of paging?

en.wikipedia.org/wiki/Paging
http://en.wikipedia.org/wiki/Memory_management_unit
http://wiki.osdev.org/Paging

Answer 1

I’m assuming you are referring the accessed and dirty bits. These bits solely exist to aid the implementation of a memory manager and do not affect the working of the MMU.

From Intel’s manual, Volume 3: System Programming, Section 3.6.4 (I’ve compacted two points into one since they are nearly identical, italic text holds only for the dirty bit):

Accessed (A) flag, bit 5 – Dirty (D) flag, bit 6

Indicates whether a page (or page table) has
been accessed (written to) when set.
(This flag is not used in page-directory entries that point to page tables.)
Memory management
software typically clears this flag when a page or page table is
initially loaded into physical memory. The processor then sets this
flag the first time a page (or page table) is accessed (for a write operation). This flag is a
“sticky” flag, meaning that once set, the processor does not
implicitly clear it. Only software can clear this flag. The accessed
and dirty flags are provided for use by memory management software to
manage the transfer of pages and page tables into and out of physical
memory.