>>Maybe, but it was a step away from interchangeable parts. Compaq had some cards which wouldn't work on other machines, and some standard cards wouldn't work on some of their machines.
>
>Maybe - but not sure if this was not a side effect stemming from implementing some routines in ROM for copyright reasons "different"

I think I remember there was even some lower level incompatibility. Electrical, IIRC - if you plug one of those where it shouldn't go, it may fry.