Handling Cache Miss

Question. You purchased a computer with the following features:

95% of all memory accesses are found in the cache.

Each cache block is two words, and the whole block is read on any miss.

The processor sends references to its cache at the rate of 109 words per second.

25% of those references are writes.

Assume that the memory system can support 109 words per second, reads or writes.

The bus reads or writes a single word at a time (the memory system cannot read or write two words at once).

Assume at any one time, 30% of the blocks in the cache have been modified.

The cache uses write allocate on a write miss.

You are considering adding a peripheral to the system, and you want to know how much of the memory system bandwidth is already used.

Calculate the percentage of memory system bandwidth used on the average in the two cases below. Be sure to state your assumptions.

a) Case 1: The cache is write through.

b) Case 2: The cache is write back.