Question

A computer uses virtual memory implemented by paging. The TLB lookup takes 100 ns and the update takes 200 ns. The PT lookup takes 1 µs and the update takes 2 µs. Loading a word from main memory onto the CPU takes 10 µs and loading a page from the disk into main memory takes 10 ms. The TLB hit ratio is 0.4 and the main memory hit ratio is 0.3. Compute the average access time for a referenced word: i.e., the time it takes • to find out the physical address • to load the referenced word onto the CPU and • to perform the necessary updates to the page tables. [Hint: Compute the access time for the possible scenarios (TLB-hit, etc.) and take the weighted average according to the hit ratios.]

Answer 1

`Hey,

Note: In case of any queries, just comment in box I would be very happy to assist all your queries

First,Search for referenced word will be done in TLB (TLB lookup) then if it is not there then it will go to main memory(main memory lookup) .if even main memory doesnot have it then disk will be accessed in order to get required referenced word.

Effective average access time = hit ratio of TLB * (TLB lookup time + time required to load page into CPU from main memory) + (1-hit ratio of TLB)*((hit ratio of main memory )*(TLB lookup time + PT lookup time + time required to load page into CPU from main memory) +( 1-hit ratio of main memory)*(TLB lookup time + PT lookup time + time required to load a page from disk to main memory + time required to update PT + time required to update TLB + time required to load a page from main memory to CPU))

Putting all values,we get

REST IS IN PICTURE BELOW:-

Kindly revert for any queries

Thanks.