It wasn't the only system. I believe that the
VIsual Commuter
could also be expanded past 640K in the base area--and it was
almost PC-compatible.
ISTR that a lot (if not all) of the early 8086/88 machines, which weren't
IBM clones, could be expanded well past 640K.
In fact, the more I think about it, ISTR that the PC was unusual in being
limited to 640K....
I definitely recall having 896K in one of my Sirii and my Apricot Xi.
TTFN - Pete.