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# Numerical: memory cost and hit ratio

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Explain the meaning of Tc, Cc, Tm and Cm in the following memory system specification.

Tc = 100 ns
Cc = 10^(-4) \$/bit
Tm = 1200 ns
Cm = 10^(-4) \$/bit

a. Calculate the cost of 1 MByte of main memory using the above parameters.
b. What is the cost of 1 MByte of cache memory?
c. If the effective access time is 10% greater than the cache access time, what would be the hit ratio (H)?

https://brainmass.com/computer-science/memory/numerical-memory-cost-hit-ratio-145900

#### Solution Preview

Tc = cache access time = 100 ns
Tm = main memory access time = 1200 ns

Cc = cost of cache memory = 10^(-4) \$/bit
Cm = cost of main memory = 10^(-4) \$/bit

a. Cost of 1 MByte of main memory (considering no cache memory)
= 1 MByte * 8 bits/Byte * Cm \$/bit
= 2^20 * 8 * 10^(-4) \$
= ...

#### Solution Summary

The solution considers that in case of a cache miss, first the content is brought from main memory into the cache and then access proceeds as if there was a cache hit. It also gives the effective access time (EAT) expression if it is not the case.

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