Address Translation

Question

A cpu generates 32- bit virtual address .The page size is 4kb .The processor has a tlb which can hold 128 entries and is 4-way set associative .The minimum size of tlb tag is ???

Comments

According to me, the answer should be 15

128 entries in 4 way set associative so , 32 sets

in a 32 bit address 5 bit for set , 12 for offset ...remaining 15 for tag

but the answer is 11

Answer 1

Answer is 11- where is that found?

Your approach is correct. 

128 entries and each set has 4 entries => 32 sets

5 set bits are required. 12 offset bits for indexing a page

Now, 32-5-12 = 15 bits are there and we need all of them to be used as tag bits as otherwise we cannot identify a page from the tag. (2¹⁵ possible page can come to a set and minimum 15 bits are needed to identify the page).