Effective Access Time(EAT) is very foremost topic in computer architecture.

The formula is very simple;

Effective Memory Access Time = Cache access time * hit rate + miss rate * Miss penalty

But following formula is the easiest formula to find EAT.

we will take an example for more clear the topic.

In a paging system, it takes 20 ns to search translation Look-aside Buffer (TLB) and 100 ns to access the main memory. If the TLB hit ratio is 80%, the effective memory access time is:

Answer:

Remember always; write first what is given data in question

TLB = 20ns , main memory access = 100ns and hit ratio = 80%

Now apply the formula,

EAT = TLB + (2 – hit ratio) * main memory access

= 20 + ( 2 – .8) * 100 ( because 80% means .8)

= 20 + ( 1.2) * 100 

= 20 + 120 = 140 ns 

Note: Use this formula to find EAT with shortcut trick.