A memory has got write through cache, primary memory

A memory has got write through cache, primary memory, and secondary memory. The access time of cache is 7 ns and 85% hit rate. The main memory has got the hit rate of 99.8% with access time of 117 ns. The average access time of the system is

(A) 20.5 ns
(B) 24.9 ns
(C) 23.5 ns
(D) 19.5 ns

Time for accessing from cache for 100 memory Tc = 85 × 7 + 15 × 117 = 2380 ns
So, Taverage = 2380/100 ≈ 23.5 ns

3Comments
Avdhesh Singh Rana @asinghrana 10 Dec 2015 08:05 pm

Here hit rate of primary memory is considered as 100%?

Udit agrawal @udit 16 Oct 2017 05:04 pm

yes ri8

Nikhil Chaurasia @nikch 3 Jan 2016 03:58 am

Why are you not considering access time of cache when there is a cache miss, in that case also cache will be accessed.??