Bit of luck today - I managed to pick up Andrew S. Tanenbaum’s Structured Computer Organization from Oxfam for ?1.49 (link is to a later edition - I got the 3rd ed., in Prentice Hall reprint). I recommend this book very highly to anyone who’s interested in how things work under the hood that’s under the hood under the hood - and how (and why) the hoods stack up. Tanenbaum is drily witty throughout, which enables him to be mildly opinionated (and hence interesting) whilst giving a broadly fair and balanced account of issues such as CISC versus RISC (although in the edition I have, we get a sense of where the debate was about a decade and a half ago…).

What? You thought I meant that SCO? Good heavens, why would anyone be interested in them?

I remain several watts short of full enlightenment on the topic of comonads.