Ars tackles caching
Hannibal has produced an excellent PYAITK article on CPU caching over at Ars Technica that's definitely worth a read. Though the article covers some pretty technical material, even newbies should be able to glean a decent understanding of caching.
In order to really understand the role of caching in system design, it helps to think of the CPU and memory subsystem as operating on a consumer-producer (or client-server) model: the CPU consumes information provided to it by the hard disks and RAM, which act as producers.
Read up, folks. The next time we break out a Linpack graph, there's going to be a quiz.