I liked John Shen's Modern Processor Design and Noam Nisan's The Elements of Computing Systems. The websites I mentioned have hobbyist-level details that are p

I liked John Shen's Modern Processor Design and Noam Nisan's The Elements of Computing Systems. The websites I mentioned have hobbyist-level details that are pretty interesting (but in general won't teach you much about things like concurrency hazards and branch prediction and so forth).