mmmh, Tricky, I'm going to have to say No.

Address space on an XT is only 1MB which contains the memory and the rombios and all the possible rom&ram on the ISA bus.
Safely testing anything above 640K would be tricky.

I think this is normal behaviour, if I recall correctly my 286 boards do the same - they treat the 384K upper memory differently.

appiah4 wrote on 2021-11-05, 12:39:

I think this is normal behaviour, if I recall correctly my 286 boards do the same - they treat the 384K upper memory differently.

it would depend on how the memory is configured on the 286.

Juko Super Turbo should count to 1024 - at least mine does.
I suspect there's something wrong with configuration - DIP switches and/or jumpers.
If you want help, you need to post a photo of the entire board, especially the switches/jumpers area...

Some 286s may do memory remapping, so the 384kB that seems lost in the bios/ROM area becomes available again. With the penalty of the roms not being shadowed.

The 808x is a different story. They just have 1MB address space as noted before. If you've got the knowledge you can experiment with the memory above 640kB and create a ramdrive there in unused address space to speed up some basic tasks (common uses tools, command.com). That's the only reasonable use I can imagine as dos and games don't expect usable ram in that area without ram driver. If you really want to get more ram, look into EMS.

Seconding what Grzyb has said, my Juko ST also counts to 1024KB at boot. The corresponding DIP switches are SW3=OFF, SW4=OFF.

I will take a few pictures of the board when i get home tonight. I can confirm both sw3 and sw4 are off. I also tried sw1 to toggle parity and this didn't make any changes either. Other than that i did shuffle the chips around in the existing banks to see if the 640 count was changed, but it didn't make a difference. My board is branded as VIP-M-813200 , BXM / 10-111. Based on the pictures of juko xt this board seems directly based off that design. Maybe the BIOS is squirrely and i need to try an actual Juko bios?

lowlytech wrote on 2021-11-05, 16:00:

Maybe the BIOS is squirrely and i need to try an actual Juko bios?

very possible

Juko-ST counts to 1024 at POST.
You won't see 1024 in checkit - only 640K. The remaining 384K can only be used with Juko's drivers e.g. CDISK.SYS, CPRINTER.SYS and CCACHE.SYS. I'm not aware of any other software that can use this memory block.

There's also some user-made EMS driver.
But it should be noted that the 384KB extension isn't available in the memory address space, only through I/O ports.
So the EMS page frame must be located below 640K, leaving only 576 KB of conventional memory.

Grzyb wrote on 2021-11-06, 00:56:

There's also some user-made EMS driver.
But it should be noted that the 384KB extension isn't available in the memory address space, only through I/O ports.
So the EMS page frame must be located below 640K, leaving only 576 KB of conventional memory.

wow imagine designing a XT class system that takes 1024kB and not providing a hardware page frame, so horribly short sighted

maxtherabbit wrote on 2021-11-06, 01:04:

Grzyb wrote on 2021-11-06, 00:56:

There's also some user-made EMS driver.
But it should be noted that the 384KB extension isn't available in the memory address space, only through I/O ports.
So the EMS page frame must be located below 640K, leaving only 576 KB of conventional memory.

wow imagine designing a XT class system that takes 1024kB and not providing a hardware page frame, so horribly short sighted

Briefly looking at a Juko XT BIOS,
It looks like there is some kind of bank-switching implemented where 0K-128K stays the same, but the 384K of RAM from 128K-512K is bank-switched. Normal mode is if 00h is written to i/o port 0E0H, bank switched mode is if 01h is written to i/o port 0E0h.
Does this sound right to anyone who has this board and has dug into it? This seems like a bad idea, any utilities wanting to mess with the bank-switching would need to disable interrupts because there might be TSRs running from 128K-512K, I think.

Using bank switching between 128kB-640kB was a common technique in DOS EMS 4.0 multi tasking setups

Indeed...
0..128K on the mobo, always present - for the operating system
128K..640K on the EMS card, quickly switchable - for userland software
I reckon such a setup was recommended for some Windows version, when it was still running in real mode.

But I doubt if there's any software to use Juko ST this way.
JUKOEMM.SYS clearly places its EMS page frame at 576K, try it yourself...

Finally had a chance to get the board photographed and dumped the BIOS. It's homemade electric tape label over the uv window is less than professional, but this is the way I received it. When I first powered it on the system physically had 768k installed but the memory count still stopped at 640k.

Only thing I have done since getting it is install an additional 2 44256 chips (the MT ones) and the 2 parity chips (Motorola ones) and change the dip settings.

BIOS also looks to be dated 4-20-88

Wow, the crystal there is 30MHz, so that would be 15MHz clock on that AMD 8088. That would be too much even for a V20.

In your BIOS, there's "Copyright (c) 1984-1988 Phoenix Technologies Ltd."
Can't verify it now, but I think the BIOS on my Juko ST is branded "NEL"
Also, I've found something "Copyright 1988 Juko Electronics Industrial Co.,Ltd.", see the attachment...

If that Phoenix BIOS is for generic XTs, then it can't possibly find the extra RAM.

Zerthimon wrote on 2021-11-06, 12:43:

Wow, the crystal there is 30MHz, so that would be 15MHz clock on that AMD 8088. That would be too much even for a V20.

Wrong.
8088 needs CLK with 33% duty cycle, so the XTAL frequency is divided by three.

Anyway, everything on the photo seems OK - just compared it with mine.
I've got eight 256Kx4 chips in the same sockets, and switches #3 and #4 are both OFF.

BTW, the sticker on my BIOS reads:

JUKO ST
BIOS version 2.32
(C) 1988 NEL ELECTRONICS LTD.

Unfortunately, I won't be able to dump it anytime soon.
Hopefully you can find it somewhere - it's newer than the "Juko ST BIOS ver 2.30" I posted earlier...