Er, yes, obscure. Can't remember where I got this, but I think it may have been CUCPS surplus. 'Micro' here really does mean pre-PC stuff. Pre-most-home-computers, in fact. The S-100 bus was the 'standard' introduced by the Altair, and this book covers that bus plus half-a-dozen others. Perhaps the only one you'd recognise today is Commodore PET. Oh, and the Apple II. These are the user-friendly ones. Most of the others come in huge boxes filled with huge PCBs. Video displays are an optional extra. 8080s, Z80s, 6800s and 6052s are the order of the day. So, this is a seriously retro book.
It's not actually very good, though. Each bus comes with a couple of photos of typical machines, a brief description of the bus, and pin-outs with minimalistic accompanying text. Not enough to design a board by - certainly no timing diagrams. Having said that, I'm not sure you really need them, since the buses are so close to the CPU buses, and anyway I think the timing requirements are rather loose. We're back in the days when you could run the bus through a couple of feet of ribbon cable with no ill effect....
I get the impression that the book's really aimed as a guide for the technical consumer. How knowing the pinouts will help in making sensible buying decisions, I don't know. Perhaps this made more sense in the late '70s?