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Suppose that a machine has $438-bit$ virtual addresses and $32-bit$ physical addresses.

  1. What is the main advantage of a multilevel page table over a single-level one?
  2. With a two-level page table, $16-KB$ pages, and $4-byte$ entries, how many bits should be allocated for the top-level page table field and how many for the next level page table field? Explain.
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The actual question contains LA as 38 Bits, not 438 Bit (Reference-book)

Ans for question 1:

To avoid the overhead of bringing a large-size Page Table into the Main Memory, Multilevel paging is implemented.

In multi-level paging, paging is applied on Page Table & instead of bringing the entire Page Table into Memory, the only page of Page Table bought into Memory.  Or A multilevel page table reduces the number of actual pages of the page table that need to be in memory because of its hierarchic structure. 

 

Ans for question 2:

 LA=38 bits

Since the pages are 16 KB,  Offsets are 14 bits (i.e 2^14 = 16 KB).

Remaining bits =   38 -14 =  24

Now this 24 bits for the page fields(i.e for outer PT and Inner PT).

as entry is 4 Bytes , one page can hold 2^12 page table entries and therefore requires 12 bits to index one page.

therefore division =(12,12,14)

 

 

 

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