I'm proud to own an old copy of How to Design, Build & Program Your Own Working Computer System by Robert P. Haviland, one of those wonderfully ambitious (but practically useless) Tab Books. Lacking step-by-step instructions or parts lists, you pretty much get vague schematics on how pieces are supposed to work together and descriptions of various methods. He briefly tells you to machine code an OS with a BASIC interpreter, then details how a BASIC program is written. It's funky. Powells has a used copy. What I'd like is Haviland's follow-up book, How to Design, Build & Program Your Own Advanced Working Computer System (which Powells doesn't have).