Thankfully there is very little of the PC or AT legacy left in current computers. Even backwards compatibility with the BIOS is starting to disappear from PCs.
Are you sure? I thought Unix, for example, came from IBM APIs. Many crusty APIs underpinning our systems today originated from proprietary products that have been preserved through caked layers of compatible interfaces, like new cities built literally on top of old ones. Sure, maybe the only APIs that are left are stuffed away deep in some broom closet and we can just throw out the whole room, but how sure are you that the APIs shuffled away in a dark corner aren't vital components required to boot or something?
IBM never got Unix. There was this saying about AIX, “it will remind you of Unix”. Unix as such came from Digital hardware, although Digital as company had some reservations adapting it.
