Assume a 2-way set associative cache with 4 blocks. You may find it helpful to d

Question

Assume a 2-way set associative cache with 4 blocks. You may find it helpful to draw a table like those found on page 482 to solve the problems in this exercise, as demonstrated below on the address sequence "0, 1, 2, 3, 4." The following table shows address sequences. Describe why it is difficult to implement a cache replacement policy that is optimal for all address sequences. Assume you could make a decision upon each memory reference whether or not you want the requested address to be cached. What impact could this have on miss rate?

Explanation / Answer

5.12.5:

Optimal page replacement algorithm is difficult to implement since it requires previous knowledge of the reference string or atleast a good prediction over it. Since there are a lots of processes working on a system without following any pattern on page usage so Optimal page replacement is tough to implement and used mainly for comparison purposes.

5.12.6:

This would bring down the miss rate to be equal to the optimal algorithm. This would simply mean that the optimal algorithm is possibly implemented giving the best possible hit rate.

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