David: in case you've forgotten the nightmare that was CP/M ... a different BIOS for every manufacturer's machine was only the start. There was then the problem that every manufacturer picked a different floppy disk formatting scheme, the better to lock out their competitors. Not to mention using different TTY control codes. This wasn't too bad for the software developers if they restricted themselves to writing code that used the BDOS and no undocumented or proprietary BIOS calls and which had some sort of bastard cousin of Termcap to figure out how to address the screen, but for high-performance stuff it was a nightmare of market fragmentation. It meant the business computer market (at least, for S-100 based CP/M boxen) was as fragmented as the UNIX market was, a decade later.

The one unequivocally good thing that the IBM PC brought was a measure of standards-based sanity, because even crap standards are better than deliberate market-sequestrating incompatability.