"Inside the Machine: An Illustrated Introduction to Microprocessors and Computer Architecture" explains the work of microprocessors—what they do and how they do it. This book definitely fills the gap between the classics—like Hennessy and Patterson titles—and other basic books that are intended for "dummies."
The book's author is Jon "Hannibal" M. Stokes, the co-founder and Senior CPU Editor of the highly popular and respected Ars Technica website. He has an awesome background and has written several technical publications and various articles related to computer architecture. He holds a degree in computer engineering from Louisiana State University and two advanced degrees in the humanities from Hardware University. He is currently pursuing a Ph.D. from the University of Chicago