Assume a system has a TLB hit ratio of 90%. It requires 15 nanoseconds to access the TLB, and 85 nanoseconds to access main memory. What is the effective memory access time in nanoseconds for this system?

310 ns

Explanation:

Given that

TLB hit ratio = 90%

TLB hit ratio = 90/100

TLB hit ratio = 0.9

Time needed to access TLB = 15 ns

Time needed to access main Memory = 85 ns

Effective memory access time = ?.

The formula for finding the effective memory access time is given by

The effective memory access time = [TLB Hit ratio (main memory access time + required time to access TLB) + [2 * (main memory access time + required time to access TLB)] * (2 - TLB hit ratio)]

On substituting the values given in the question to the equation, we have

The effective memory access time = [0.9 (85 + 15) + [2 * (85 + 15)] * (2 - 0.90)]

The effective memory access time =

[(0.9 * 100) + (2 * 100) * 1.1]

The effective memory access time =

(90 + (200 * 1.1))

The effective memory access time =

90 + 220

The effective memory access time =

310 ns

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