[Proud_texan]

Copyright issues. A direct copy would have been illegal and IBM would have crushed them. If I recall correctly the clones did exactly what is described in the program; put programmers in a locked room and described a task and had them come up with a solution independent of the actual IBM solution.

And it's been a while but I seem to recall one of the more difficult parts was the section of the BIOS that read "COPYRIGHT IBM". I'm pretty sure the IBM version of DOS read the BIOS and looked for that string and if it wasn't there it wouldn't load.

But since IBM didn't have an exclusive on DOS from Microsoft it was possible for the clone makers to come out with their own versions with subtle differences thus you had Compaq DOS, etc. After a bit MS produced generic versions branded by them.

[AU72]

When negotiating with MS on MSDOS IBM's legal team didn't want to own MSDOS fearing liability issues so they agreed to let MS keep it and pay them a license fee for each unit.

Worse deal ever made until last week.