.::Virtual Memory::.

Each process is given its own 32-bit address space.

• This means that an address space in one program is different form the same address space in another program.

Paging – is used to remap an virtual address within one program to different physical addresses in memory. The Pentium uses a page frame size of 4,096 bytes, which is physical memory, and has 2^20 different pages in virtual memory space.

OS keeps track of pages to page-frames.

Page table – is used to translate the H.O. bits of a virtual address to select a page. The L.O. bits of the virtual address are used as an index into the page. Mapping between virtual and physical addresses is given below.

Page Table Entries

• Validity bit – set to 0 if the next page is not in memory
• Frame number – number of bits required depends on size of physical memory
• Protection bits – read, write, execute accesses

To prevent cluttering the data cache with page table entries the page table uses its own cache know as the TLB. This cache usually has 32 entries on a Pentium processor.