Probably a n00b question but where did the commented machine code come from? Did IBM publish their original PC BIOS code, comments and all? Was the original "PC clone" bios just a clean room reimplementation?
Yes, there was a gray fabric covered binder that had the full source code. I got a copy somehow in the mid 80s as a teenager. I poured over the bios code which made me ace my assembler class years later in college (along with reading the pink shirt book).