calculate the effective access time

Question

This is a paragraph from Operating System Concepts, 9th edition by Silberschatz et al:

The percentage of times that the page number of interest is found i

Answer 1

In TLB a copy of frequently accessed page number and frame no is maintained which is from the page table stored into memory.

It first looks into TLB. If found, it goes to the memory location so the total access time is equals to:

20 + 100 = 120 ns

Now if TLB is missing then you need to first search for TLB, then for the page table which is stored into memory. So one memory access plus one particular page acces, nothing but another memory access. So the total time is equals to:

20 + 100 + 100 = 220 ns

And effective memory access time is equals to:

0.80 * 120 + 0.20* 220 = 140 ns