If that system has 16 bit ISA slots, the best way forward would be a combined 16-bit extended/expanded memory card, on which you can provide at least 256K of extended memory (you actually require only 64K of extended memory to make DOS=HIGH work) and also provide expanded memory using another part of the memory installed on that card. As far as I know, these card are hard to get nowadays, though.

mkarcher wrote on 2026-02-08, 23:02:

If that system has 16 bit ISA slots, the best way forward would be a combined 16-bit extended/expanded memory card, on which you can provide at least 256K of extended memory (you actually require only 64K of extended memory to make DOS=HIGH work) and also provide expanded memory using another part of the memory installed on that card. As far as I know, these card are hard to get nowadays, though.

Yeah. Maybe guaranteed compatibility is with one of those intel above board jobs.

The official memory board for my machine is an MH1476A, but guess I've got more chance stumbling across a unicorn..

If you only have 640k of RAM installed, it's impossible to use high memory. Even some 286s with 1MB can't use high memory if they lack the ability to re-map 384k out of the UMB area and into extended memory.

I don't know why you refer to this system as an "XT286". Normally that refers either to IBM 5162 specifically, or a 286 system that only has 8-bit expansion slots. Your machine is an AT clone. Get yourself a 16-bit RAM expansion card and make sure whatever you buy is documented as they usually have a lot of DIP switches on them.

Anonymous Coward wrote on 2026-02-09, 09:49:

If you only have 640k of RAM installed, it's impossible to use high memory. Even some 286s with 1MB can't use high memory if they lack the ability to re-map 384k out of the UMB area and into extended memory.

I don't know why you refer to this system as an "XT286". Normally that refers either to IBM 5162 specifically, or a 286 system that only has 8-bit expansion slots. Your machine is an AT clone. Get yourself a 16-bit RAM expansion card and make sure whatever you buy is documented as they usually have a lot of DIP switches on them.

Ok. Maybe it's the Sperry predecessor with similar specs that's called an XT and I'm confusing it with that then.
Keep you updated.

I'm really quite surprised that a 16bit community sram card hasn't appeared. some modifications of the lotech EMS design for 16bits instead of 8 (more bus logic transievers, either doubled memory sockets for hi/low bytes, or 16bits wide sram-- hi/low would be a more straightforward path from the ref design), with some additional jumper glue for some of the memory to appear directly on the bus above 1M (xms), and you'd have it. (One 64kb chunk of EMS in the 384k area can just be UMB if ems is disabled. )

There's a valid community need for a 16mb XMS ISA card, since things like the compaq portable used a custom ram card that is now unobtanium, but an ISA card will work.

For 286 and 386slc (with 16bit external bus), it would be a very valuable/useful card.

If I was any good at board design it would be worthwhile to do. Sadly, I never got into that.

Here I remember hy halved Bocaram AT card 😉
Bocaram AT XMS/EMS memory card replica?

Should be an easy job to recreate it, but I dont know how this works, too.