[paulmd]

I very much recommend Agner Fog's Microarchitecture. It's a rather ponderous tome, but it is quite simply the definitive resource on the actual design and performance of real-world x86 CPUs.

It does have a brief introduction on some of the basic execution fundamentals but then it jumps right in, so you will probably need some external introduction if you are not generally familiar with the topic.

http://www.agner.org/optimize/microarchitecture.pdf