NIELIT Scientist B 2020 November: 85

Question

If main memory access time is $400\;\mu s$, $TLB$ access time $50\;\mu s$, considering $TLB$ hit $90\%$, what wil be the overall access time?

• A. $800\;\mu s$
• B. $490 \;\mu s$
• C. $485\;\mu s$
• D. $450\;\mu s$

Answer 1

EMAT $=$ TLB hit $\times$ (TLB access time $+$ memory access time) $+$ TLB miss(TLB access time $+$ page table access time+memory access time)

$\implies$ EMAT $ = \dfrac{90}{100}(50+400) + \dfrac{10}{100}(50 + 400 + 400) \:\mu s$

$\implies $ EMAT $ = \dfrac{9}{10}(450) + \dfrac{1}{10}(850)\:\mu s$

$\implies $ EMAT $ = 9 \times 45 + 85 \:\mu s = 405 + 85 \:\mu s = 490\:\mu s.$

Ref: https://gateoverflow.in/2067/gate2014-3-33

So, the correct answer is $(B).$