dumped the PROM. it seems to be part of the address decoding process or memory mapping.
so this board looks like it does both XMS (extended memory) and EMS (expanded memory). expanded memory is banked and uses a 64K (iirc) window to access it.
@tubetime Ahhh, so it's like the AST RAMpage 286 :D!
well crap, this board appears to be a clone of the Intel Above Board Plus 8 card. it sure looks the same!
yeah sure looks identical. welp, now we know how it works, lol.
OK, here are the KiCad files. it's not really a fab-able design because there are still DRC errors, but at least the schematic is useful.
https://github.com/schlae/XebecAboveBoard
@tubetime but has it ever been reverse engineered before…? That would be a bummer. But if not: success!
Gregory's Server
so this board looks like it does both XMS (extended memory) and EMS (expanded memory). expanded memory is banked and uses a 64K (iirc) window to access it.