bhtooefr
Experienced Member
I've got a U44 PROM that is non-stock on my XT 64-256K board, and am wondering if this is someone's one-off custom ROM (and therefore would require dumping the ROM or lots of experimenting to see what settings are available on it) or one that's documented somewhere and I haven't found the documentation.
Memory configuration of the system is with 64k DRAMs in banks 0 and 1, 256k DRAMs in banks 2 and 3. It's worth noting that this is contrary to how IBM boards did it (256k in 0 and 1, 64k in 2 and 3), and it's contrary to how HIMEMV2's E2 off/off config works (64k in 0 and 3, 256k in 1 and 2).
E2 jumpers: Off/Off (C-F)
SW2 table:
Off/Off (F): 640k detected (which is what's installed, although not the normal way (of banks 0 and 1 being filled with 256, and not HIMEMV2's way either)
Off/On (E): 128k detected (either this is just bank 0 and 1 at 64k, which makes little sense, or it's an even more insane layout that makes even less sense)
On/Off (D): 384k detected (bank 0 and 1 at 64k, and 2 at 256k, ignoring 3?)
On/On (C): 64k detected (I suspect this is looking for 256k in bank 0, and failing, but who knows, it could be a bank 0 at 64k and nothing else config)
I suspect this came in an upgrade kit, as U44 has yellow tape on it, and U84 has pink tape on it, if that helps with identification.
Bonus points if someone can identify the right config to get (presumably with 41256s in all the positions, or maybe in all but one bank?) an equivalent config to HIMEMV2's map 2 or 3 (which fills all banks except C (for HDD ROM and NIC RAM conflict reasons), D or E (to give me somewhere to stick an EMS 3.2 page frame), and F (also for ROM conflict reasons), for a total of 816 KiB usable on a CGA system (832 KiB mapped, but 16 KiB overlapping CGA)).
And, yes, I'm aware that a better config would be something that would get me 256k or less detected, and use EEMS, XMA, or a true EMS 4.0 board to backfill, because then an EMS 4.0 driver could bankswitch it all.
Memory configuration of the system is with 64k DRAMs in banks 0 and 1, 256k DRAMs in banks 2 and 3. It's worth noting that this is contrary to how IBM boards did it (256k in 0 and 1, 64k in 2 and 3), and it's contrary to how HIMEMV2's E2 off/off config works (64k in 0 and 3, 256k in 1 and 2).
E2 jumpers: Off/Off (C-F)
SW2 table:
Off/Off (F): 640k detected (which is what's installed, although not the normal way (of banks 0 and 1 being filled with 256, and not HIMEMV2's way either)
Off/On (E): 128k detected (either this is just bank 0 and 1 at 64k, which makes little sense, or it's an even more insane layout that makes even less sense)
On/Off (D): 384k detected (bank 0 and 1 at 64k, and 2 at 256k, ignoring 3?)
On/On (C): 64k detected (I suspect this is looking for 256k in bank 0, and failing, but who knows, it could be a bank 0 at 64k and nothing else config)
I suspect this came in an upgrade kit, as U44 has yellow tape on it, and U84 has pink tape on it, if that helps with identification.
Bonus points if someone can identify the right config to get (presumably with 41256s in all the positions, or maybe in all but one bank?) an equivalent config to HIMEMV2's map 2 or 3 (which fills all banks except C (for HDD ROM and NIC RAM conflict reasons), D or E (to give me somewhere to stick an EMS 3.2 page frame), and F (also for ROM conflict reasons), for a total of 816 KiB usable on a CGA system (832 KiB mapped, but 16 KiB overlapping CGA)).
And, yes, I'm aware that a better config would be something that would get me 256k or less detected, and use EEMS, XMA, or a true EMS 4.0 board to backfill, because then an EMS 4.0 driver could bankswitch it all.
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