Reverse engineering a forgotten 1970s Intel dual core beast: 8271, a new ISA

Around 1977, Intel released a floppy disc controller (FDC) chip called the 8271. This controller isn’t particularly well known. It was mainly used in business computers and storage solutions, but its one breakthrough into the consumer space was with the BBC Micro, a UK-centric computer released in 1981.

There are very few easily discovered details about this chip online, aside from the useful datasheet. This, combined with increasing observations of strange behavior, make the chip a bit of an enigma. My interest in the chip was piqued when I accidentally triggered a wild test mode that managed to corrupt one of my floppy discs even though the write protect tab was present! You can read about that here.

Can we reverse engineer a detailed understanding of how it works? What wonders will we find?
↫ Chris Evans

This thing is wild.