Two Level Page Table In Os

It is also known as hierarchical paging.

Two level page table in os.

Thus here our outer page table page table 2 can be stored in one frame. So size of outer page table 2 10 4b 4kb. Prerequisite paging multilevel paging is a paging scheme which consist of two or more levels of page tables in a hierarchical manner. A page offset consisting of 12 bits.

A logical address on 32 bit machine with 4k page size is divided into. Each page table including the top one has only 1024 entries few enough to fit comfortably within a 4k page. What s the size of a single page. One for each block of 2nd level page table.

The page tables or page map levels are used to map each virtual page to a corresponding physical page zero or more virtual pages can correspond to the same physical page. The sizes of the page table directory the table directory and the page are equal. The offset remains same in both the addresses. The size of a page depends on the processor mode protected compatibility or long mode the extensions used e g.

A simple technique is a two level page table. A page number consisting of 20 bits. Multi level page tables. The cpu has two level paging and the logical and physical addresses are of 34 bits size each.

A multitasking os need to manage different memory maps for the different running applications so there can be several copies of the page tables. This is two level paging because here we got 2 page tables. If there is less memory installed the page tables can be smaller with invalid or unmapped entries in the first level page table. It converts the page number of the logical address to the frame number of the physical address.

The logical address 12345678 16 has been translated to the ba9678 16 physical address. This size is only needed for mapping the whole 4gb address space. We look up the first page table to find the second table then look up the second table to find the frame in which the page is stored. Page tables can be limited to one page more easily be paged out and multiple page faults possible.

For example let us take that 20 bit page number and split it into two 10 bit indices. The page table stores all the frame numbers corresponding to the page numbers of the page table. Of pages of the page table 2 outer page table 2 22 2 12 2 10 pages. To perform this task memory management unit needs a special kind of mapping which is done by page table.

Thus we can stop here.