UGC NET CSE | December 2019 | Part 2 | Question: 27

Question

Consider a paging system where translation look aside buffer ($\textsf{TLB}$) a special type of associative memory is used with hit ratio of $80 \%$.

Assume that memory reference takes $80$ nanoseconds and reference time to $\textsf{TLB}$ is $20$ nanoseconds. What will be the effective memory access time given $80\%$ hit ratio?

• A. $110$ nanoseconds
• B. $116$ nanoseconds
• C. $200$ nanoseconds
• D. $100$ nanoseconds

Answer 1

Effective memory access time= time for address translation+ actual memory access time for accessing a word.

During address translation, we check in TLB. If the entry is not available in TLB, memory is accessed for the entry.

Once the address is translated, we access main memory to get the word.

=TLB access time+(miss rate of TLB)* memory access time+ memory access time

=20+(1-80/100)*80 +80

=20+80/5+80

=116ns.