TEST Series

Question

Consider a paging system with page table stored in main memory i) memory reference takes 200 ns and ii) if we add associative registers and 75% of all the page table references are found in the associative registers, the effective memory access time is ________ ns.

Comments

Here Register access time not given i assume it is 0ns

so EMAT= 200ns + 0.25$\times$ 200ns = 200 + 50 = 250 nsec

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Why 200+50 , 75% of the time we going for associative registers , thus once page reference is made we should go to MM to fetch the page frame , so it shd be .75*(0+200)  +.25(200+200+0)

Bcz...when it's not in associative reg , we have to check MM , in this case ,

First , associative reg will be checked , 0ns ( page ref unsuccessful)

Then , page table in MM will be checked ( assume that no page fault will happen , thus 200ns )

at last , that page frame would be fetched from MM ( 200ns)