Question

If the user has a system with 80% hit ratio, time for
searching the associative registers is 50 ns and time for
accessing the memory is 750 ns then what is the time to
access a page if the page number is not available in
associative memory?
A 800 ns
B 1550 ns
C 750 ns
D None the above
​

Answer 1

Given :- If the user has a system with 80% hit ratio, time for searching the associative registers is 50 ns and time for accessing the memory is 750 ns then what is the time to access a page if the page number is not available in associative memory ?

A) 800 ns

B) 1550 ns

C) 750 ns

D) None the above.

Solution :-

we know that,

• Effective Access Time = Hit ratio of TLB * { Access time of TLB + Access time of main memory } + Miss ratio of TLB * { Access time of TLB + (L+1) * Access time of main memory } .

• L = Number of levels of page table .

from given data we have :-

• Number of levels of page table = 1
• TLB access time = 50 ns
• Main memory access time = 750 ns
• TLB Hit ratio = 80% = 0.8

So,

→ TLB Miss ratio = 1 - TLB Hit ratio = 1 - 0.8 = 0.2 .

Putting all values in given formula now we get :-

→ Effective Access Time = 0.8 * { 50 ns + 750 ns } + 0.2 * { 50 ns + (1+1) * 750 ns }

→ Effective Access Time = 0.8 * 800 + 0.2(50 + 1500)

→ Effective Access Time = 640 + 0.2 * 1550

→ Effective Access Time = 640 + 310

→ Effective Access Time = 950 ns. (Ans.) (Option D).

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