Question

Let the memory access time is 10 milliseconds and cache miss ratio 15% .The effective memory access time is ?
1. 2 milli seconds
2. 1.5 milli seconds
3. 1.85 micro seconds
4. 1.85 milli seconds

Answer 1

Correct Answer - Option 2 : 1.5 milli seconds

Data:

Cache

Cache = T1 = 0 ms (since not mention)

Hit ratio = 15%

Hit ratio = 100% - 15% = 85% = 0.85

Miss ratio = 1 – 0.85 = 0.15

Main memory

Main memory = T2 = 10 ms

Formula:

Average memory access time = Tavg = H1T1 + (1- H1)(T1 + T2)

Tavg = T1 + (1- H1)(T2)

Calculation:

Tavg =  0 + (1- 0.85)(10)

∴ Tavg = 1.5 milli seconds