Petzold provides the clearest, most easily understood explanation of computers I've ever heard. He starts from the very BASICS - ones and zeroes, and starts with a story about flashlights that explains things in such a way that you not only understand how things work, but you understand WHY they work the way they do, and why it's the best way.

for CWRU people, the material in this book is pretty much EECS 281. If any non-computer science people are curious as to why computers work the way they do, I highly, HIGHLY recommend this book.