[jws]

An application that is aware of the half dozen of so caching layers from register to platter can perform dramatically better than a naive program. Two wrinkles:

1) it needs to either be told the various sizes, speeds, and quirks on each server to make best use. (just some work)

2) it needs to coordinate with the other processes running on the system to divide up the resources. This is hard. Generally people bail and just assign some share of RAM and hope for the best with the other layers.