Probably the onboard IDE interface.

Try disabling the onboard IDE interface of the card and see whether the problem disappears.
Chances are that you're not going to use it.

Unfortunately I can't disable the SB16's ide interface from the device manager. But I just can't figure out why Windows isn't able to recognize it. Windows 98 and XP should not have all the drivers for it?

Maybe that's a stupid question, but did you enable ACPI and APIC options in the Setup Utility ?
And is the "PnP aware OS=Yes" option also set ? Windows can't handle IRQ and I/O managment if these are disabled.
Note, that these have to be set before you do an installation of Windows, as these selections have an influence on which kernel is choosen.

To be sure, I've made a new Windows installation, but nothing has changed.
It could be that Windows 98 and XP do not support ide controllers instead of the onboard ones?
Surely, is something about that, because BEFORE the chipset drivers installation the question mark says "PCI to ISA bridge". AFTER I install the driver for the ISA bridge it detects the unknown device.
It really doesn't make any sense to me

I see. Your CT2940 doesn't have any jumpers.. That's bad in this case.
You could try to use intels Configuration Manager (ICM) to change settings.
It can be run from Windows 3.1 or DOS. So maybe it's also usable in Win 9x.

PnP configuration may be unable to hide the IDE port, because Windows seems to often do whatever it wants anyway. The card is also available sans IDE, so a hardware mod (ie. cut some leads) might disable it.

The other option would be to actually source a driver for the thing, if it exists.

Thanks, I haven't thought of that. Is there another way ?
Any chance the resources for onboard IDE can be changed somehow ?
So they won't interfere with the secondary IDE interface on the SB16 ?

Maybe it helps to assign IRQ15 to "Legacy ISA" (PNP/PCI configuration).

Nothing changes, unfortunately

Ok. Can you disable the onboard IDE completely and boot from that SB16 IDE ?
I'm curious whether this "fixes" the problem with the yellow mark.

Hello, i have a sound blaster 16 ct2950,probably quite similar to yours. I have tried this card on a 486 dx2 66, expertboard exp8046 motherboard, in both dos and windows 95

In windows 95 this 2950 shows the same 'unknown' or 'unsupported' device problem with win95 drivers but the sound card works flawlessly .
I've tried reinstalling the sb16 drivers included in the ! awe64 ! installation disks (found it in SB supercompilation here on this forum, thanks ) and ... unsupported device recognized!

I wonder why there's sb16 support in awe64 drivers, i'm no expert on this, but this trick worked!

I still have a really annoying systray error showing off at every boot caused by sb16snd.drv using both 'default' and the awe64 drivers, and that's why i've decided to switch to my ess1868 sound card.

I'd like to install this Sound blaster on a different pc and on a fresh windows installation, just to see if i can avoid these problems entirely.

Oh, also sorry for my poor english, it is not my main language 😊

Thank you very much for your help! It finally works!!! I don't know why Windows 98 and XP use an older driver, but it doesn't matter.
Problem solved 😉