The facilities provided by OS (as in BIOS and M$DOS) for COM and LPT are rather limited to line printing and rudimentary character input/output. Also, the interfaces were poorly defined and extensions were usually improvised.

These resources can be - and were indeed - used much better in many applications. The trouble is that this sort of applications did not use PC as a office tool, hence the lack of support.

That many of the office use software were (are) buggy and playing fast and loose, that's a different story.

Also, there is no reason why a '51 could not have an OS, whatever it means, and isolate the hardware from software, it's just impractical.

Once you start inserting layers between software and hardware (or between software and software), you are loosing flexibility and resources (mainly speed) anyway. You do this in the name of universality, which sounds as a good idea and indeed in many cases it is - as long as there is a way how to fall back in the special cases (e.g. reboot to DOS-ish anything and play with the ports again). Now this is what ceases to be possible with the "legacy-free" PC.

JW