A 286 board with 1MB counting only 640K is usually not OK. Memory was very extensive those days, and wasting 37,5% by default was inacceptable.

First, make sure you indeed have two banks of 512K, not one bank of 512K and one bank of 128K. Then check whether you can enter 384KB of extended memory in the BIOS setup (possibly using a specific software tool for your system or a generic program like gsetup).

Stuff like shadowing, EMS and sometimes UMBs only appeared in the later 286 days. Can you tell is more about your 286 board (what chipset if any, what BIOS vendor, ...) if you need further assistance?

mkarcher wrote on 2021-09-07, 08:02:

A 286 board with 1MB counting only 640K is usually not OK. Memory was very extensive those days, and wasting 37,5% by default was inacceptable.

First, make sure you indeed have two banks of 512K, not one bank of 512K and one bank of 128K. Then check whether you can enter 384KB of extended memory in the BIOS setup (possibly using a specific software tool for your system or a generic program like gsetup).

Stuff like shadowing, EMS and sometimes UMBs only appeared in the later 286 days. Can you tell is more about your 286 board (what chipset if any, what BIOS vendor, ...) if you need further assistance?

Both banks are four chips of 256Kx4, for a total of 1024Kx4 (512KB) in each. Board is made in 1991 and has option to map 384K to Extended. Question is, is it better to use it as UMB in <1MB area or as Extended in >1MB area?

There are known two good solutions which provides UMB memory for 286 systems. However, it depends on the chipset ...

UMBDRVR: http://www.win3x.org/win3board/viewtopi ... anguage=en
and
The last byte memory manager http://files.mpoli.fi/unpacked/software ... ntents.doc

appiah4 wrote on 2021-09-07, 08:30:

mkarcher wrote on 2021-09-07, 08:02:

A 286 board with 1MB counting only 640K is usually not OK. Memory was very extensive those days, and wasting 37,5% by default was inacceptable.

First, make sure you indeed have two banks of 512K, not one bank of 512K and one bank of 128K. Then check whether you can enter 384KB of extended memory in the BIOS setup (possibly using a specific software tool for your system or a generic program like gsetup).

Stuff like shadowing, EMS and sometimes UMBs only appeared in the later 286 days. Can you tell is more about your 286 board (what chipset if any, what BIOS vendor, ...) if you need further assistance?

Both banks are four chips of 256Kx4, for a total of 1024Kx4 (512KB) in each. Board is made in 1991 and has option to map 384K to Extended. Question is, is it better to use it as UMB in <1MB area or as Extended in >1MB area?

better to use it as extended IMO

you will save nearly 64kb of conventional by loading DOS high if you have extended, plus the programs that support using extended directly

if you plan to add an expansion card for extended memory, then it would make more sense to use the extra motherboard memory as UMB

appiah4 wrote on 2021-09-07, 08:30:

Both banks are four chips of 256Kx4, for a total of 1024Kx4 (512KB) in each. Board is made in 1991 and has option to map 384K to Extended. Question is, is it better to use it as UMB in <1MB area or as Extended in >1MB area?

I would have thought 4 chips of 256Kx4 would be organised as 256Kx16, as it's a 16 bit system. Just a little nip-picking, but it does make a difference when/if you move the chips around if you think that it retains the bandwidth of chips vs banks.

debs3759 wrote on 2021-09-07, 13:39:

appiah4 wrote on 2021-09-07, 08:30:

Both banks are four chips of 256Kx4, for a total of 1024Kx4 (512KB) in each. Board is made in 1991 and has option to map 384K to Extended. Question is, is it better to use it as UMB in <1MB area or as Extended in >1MB area?

I would have thought 4 chips of 256Kx4 would be organised as 256Kx16, as it's a 16 bit system. Just a little nip-picking, but it does make a difference when/if you move the chips around if you think that it retains the bandwidth of chips vs banks.

You are right, and my assumption is probably wrong. I have checked the memory configurations of various similar boards using the same chipset and they are 256Kx16 per bank indeed 😀