ArsTechnica is fairly well-known on the Internet for their articles on CPU architectures, typically released shortly after a new CPU is released. Jon Stokes is the man behind them - and it turns out he's been busy writing a book. Check out some preprint images.
While not exactly Henessey and Patterson's Computer Architecture, I'm pretty sure it'll be a fine read for anyone who wants to learn more about the details of CPUs.
Inside the Machine (ArsTechnica computer architecture book)
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