If you're looking for an extensive guide to the hardware workings of PCI, this is THE book. I read it, then bought the PCI spec (because I needed mechanical info). After looking through the spec, I realize that PCI System Architecture covers every aspect of conceptual, and almost all detail, information that is in the spec. As far as specs go, the PCI spec is very readable, but this book turns the PCI spec into a "for dummies" book in the sense that it's so easy to follow. Numerous and overlapping examples make it clear what's going on, and by the time you're done reading, you can do this stuff in your sleep. Only things absent were: (1) Mechanical info (though for $50, you really should buy the spec), (2) How to initiate transactions (in software) from an x86 PC, particularly burst transfers.