[COA] Memory Access

Question

A computer has a cache, main memory, and a disk used for virtual memory. If a referenced word is in the cache,Cpu access it from cache.. If it is in main memory but not in the cache, 50 ns are needed to load it into the cache, and then the reference is started again. If the word is not in main memory, 16 ms are required to fetch the word from disk, followed by 50 ns to copy it to the cache, and then the reference is started again.The cache hit ratio is 0.7 and the main memory hit ratio is 0.8.What is the average time in nanoseconds required to access a referenced word on this system.Cache access time is 5 ns ,Main memory access time is 10 ns.

 

Edit:- Disk accessed was mentioned twice.Updated it

Comments

Once we have tranferred to cache ,then shall we add 5ns again to access it from cache or not?

EAT(Effective Access Time) = Cache hit rate * Time to access the word from Cache + Cache Miss rate *((Main Memory Hit Rate * (Time taken to access the word from cache in absence of cache+Cache access)) + MM miss rate *(Cache access time + MM access time + Hard Disk Access time+Cache Access))

In the end after transferring data to cache ,should we access from cache now to complete the access time?

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@ pawan kumarln,@akash.dinkar12

Can you clear my doubt above please?

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i have the same doubt