Consider a single-level page table system. with the page table stored in the memory. If the hit rate to TLB is 80%, and it takes 15 nanoseconds to search the TLB. and 150 nanoseconds to access the main memory, then what is the effective memory access time, in nanoseconds ?

Question

Question

This question was previously asked in

UGC NET Computer Science (Paper 2) 2020 Official Paper

Answer 1

Data:

TLB hit ratio = p = 0.8

TLB access time = 15 nanoseconds

Memory access time = m = 150 milliseconds

Formula:

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

Calculation:

EMAT = 0.8 × (15 + 150) + (1 – 0.8) × (15 + 150 + 150)

EMAT = 195 nanoseconds.

Important points:

During TLB hit

Frame number is fetched from the TLB (15 ms)

and page is fetched from physical memory (150 ms)

During TLB miss

TLB no entry matches (15 ms)

Frame number is fetched from the physical memory (150 ms)

and pages are fetched from physical memory (150 ms)