Question

Consider a paging hardware with a TLB. Assume that the entire page table and all the pages are in the physical memory. It takes 10 milliseconds to search the TLB and 80 milliseconds to access the physical memory. If the TLB hit ratio is 0.6, the effective memory access time (in milliseconds) is_____

Answer 1

Data:

TLB hit ratio = p = 0.6

TLB access time = 10 milliseconds

Memory access time = m = 80 milliseconds

Formula:

EMAT = p × (t + m) + (1 – p) × (t + m + m)

Calculation:

EMAT = 0.6 × (10 + 80) + (1 – 0.6) × (10 + 80 + 80)

EMAT = 54 + 68

EMAT = 122 milliseconds.

Important points:

During TLB hit

Frame number is fetched from the TLB (5 ms)

and page is fetched from physical memory (100 ms)

During TLB miss

TLB no entry matches (5 ms)

Frame number is fetched from the physical memory (100 ms)

and pages are fetched from physical memory (100 ms)