Do your original 1MB SIMMs have 3-chips or 9? What about the 4MB SIMMs?

I would say some bug in the CD-ROM driver...
Have you tried various drivers?

try with 2x4M +2x1M modules, just for fun 😀

1m simms have 3 chips, the 4m ones have 9.
tried with various drives and various drivers. will check again, also trying the 4+4+1+1 combo now.

some test results:
same creative32x cdrom

4x1meg rams:
oakcdrom.sys - not working (numlock and tcrl-alt-del is responsive)
vide-cdd.sys - works flawlessly
gscdrom.sys - not working: mostly hard freeze, once there was a restart.

2x1meg+2x4meg (2x1megs in lower address space, 2x4meg in higher address space):
oakcdrom.sys - not working (numlock and ctrl-alt-del responsive)
vide-cdd.sys - works
gscdrom.sys - hard freeze

2x1meg+2x4meg(1megs in upper, 4 megs in lower address space)
no POST

2x4 megs in lower address space:
oakcdrom.sys - soft freeze, as always
vide-cdd.sys - hard freeze
gscdrom.sys - hard freeze

2x4 megs in upper address space:
no POST

8x4megs:
oakcdrom.sys - soft freeze
vide-cdd.sys - hard freeze
gscdrom.sys - hard freeze

any ideas?
could it be a hardware issue?

I'm just guessing here... If I encountered this situation... which sadly I can't since the only two 286 mainboards I have are annoying when it comes to memory, one is limited to 4M and the other is an old ibm with 512K...

I'd try more cdrom drivers, try the freedos ones, or freedos itself. With 16MB i'd even try an old OS2... no idea if it has ide cdrom support 😀

The "no POST" configurations are expected. Dual-bank 286 boards often do not tolerate the first bank being unoccupied, and require the second bank to not have modules that are smaller than the modules in the first bank. The CD driver issue looks like oakcdrom.sys and gscdrom.sys generally are incompatible with your system (for whatever reason), so the interesting question is why vide-cdd.sys only works in some configurations. I notice the pattern that vide-cdd.sys works as long as the low bank is not using the 4M simms, so it is likely that you indeed have problems with the 4M modules, in a way that memtest does not fail, but the CD driver does.

Memory problems that are not found by memtest could be refresh problems, but the refresh requirements for 9-chip 4M modules and 3-chip 1M modules are often the same (requiring a 10-bit counter, and refreshing one row per 16µs). Can you read the type number of the memory chips? What chipset does the mainboard use?

Good points mkarcher !
What motherboard / chipset are you using is important for us to know. Did that motherboard come natively running at 25Mhz or is that just the 286 cpu rating ?
Also: What IDE controller are you using and What version of DOS are you running ?

What do you mean by "memtest"?
I guess it's neither MemTest86 nor Memtest86+, as I never could get them to work on a 386, leave alone a 286...
My preferred tools for memory test on a 286 are:
- Checkit 3.0, with "quick memory test only" set to NO
- Checkit Pro 1.11, also with some "comprehensive" option

Anyway, if there's only one driver (VIDE-CDD.SYS) that works depending on the memory amount, there's still the option that the driver is buggy - so try more drivers.

If you can't find a working driver for ATAPI drives, there's still the option that's more appropriate for a 286: one of those proprietary-interface drives, like Misumi, Panasonic, Sony...

My suspicion is that the chipset on this board does not actually support 4MB SIMMs. But why it POSTs and counts all the memory, I can't resolve with my theory

You need to make sure (on a 286) with 16mb

That the bios does not try to relocate or use the 384kb of memory as extended

The drivers you are using aren’t trying to go up to the very top of memory

My best guess is the driver is trying to use a memory location that is mapped to something else.

Most 286’s need to put a memory hole at the top of memory for 16 bit ISA cards that use the top of the memory space,
many do not

The 384kb area also needs to be a memory hole.

Most 286’s handle 12mb much more successfully.

Grzyb wrote on 2021-05-08, 00:02:

What do you mean by "memtest"?
I guess it's neither MemTest86 nor Memtest86+, as I never could get them to work on a 386, leave alone a 286...

Do not try Memtest86+ past version 4.10

What was the behaviour with 8mb?

maxtherabbit wrote on 2021-05-08, 01:56:

My suspicion is that the chipset on this board does not actually support 4MB SIMMs. But why it POSTs and counts all the memory, I can't resolve with my theory

That's a possibility. Though I've never seen a 286 myself that couldn't handle 4MB mimimum (1MB SIMMs).

Not sue about 4MB SIMMs, though.
Occupying the full 16MB address space isn't trouble free perhaps.
Some ISA VGA's used the 15-16MB region for the frame buffer.
That region is ATs' counterpart to the 640KB-1024KB range of the PC/XT or the 3,5GB-4GB range of Pentium era PCs.

Btw, by definition, a "chipset" was something that the more sophisticated 286 PCs had (NEAT and successors).

And such sophisticated PCs surely were meant to be able to run a real OS, like OS/2 or Xenix,
or Netware, which in turn required lots of RAM.
Okay, enough nitpicking. I'm quite now. 😇

There were very few true AT-clones brought to market that used discreet logic for everything. The vast majority of clone boards used a chipset of some kind, most of which did little more than provide basic AT functionality.

OP's system does work fine with 4x1MB SIMMs. OAKCDROM does NOT work on a 286 period, regardless of memory - it requires a 386. I can't speak to the GS whatever one because I've never tried it, but I suspect the issue is the same.

Ah, I see. I've used a PAS16 and the Trantor driver on my 286 back then.

Edit: Does OAKCDROM use 386 Real-Mode instructions? If so, EMU386 could help.

Jo22 wrote on 2021-05-08, 18:43:

Ah, I see. I've used a PAS16 and the Trantor driver on my 286 back then.

Edit: Does OAKCDROM use 386 Real-Mode instructions? If so, EMU386 could help.

Does EMU386 work for other installable device drivers? That would be an interesting solution but I'm a bit skeptical that it would work

Jo22 wrote on 2021-05-08, 04:01:

That region is ATs' counterpart to the 640KB-1024KB range of the PC/XT or the 3,5GB-4GB range of Pentium era PCs.

That is just an NT issue and not a hardware issue I believe.