Hello,
I have an Asus ISA-386C (https://theretroweb.com/motherboards/s/asus-isa-386c) which seems to generate unusual video artifacts when used a specific combination of I/O cards and CF cards. I suspect this relates to certain combinations setting IDE I/O modes (like DMA etc) that causes this, but I was hoping that someone knew exactly what was going on here and could explain it. Even with the artifacts the computer actually runs fine, for example I can play Doom (albeit with a very poor framerate) even with this going on, it doesn't crash it just has a few incorrect pixels.

Here's what's in the system
Asus ISA-386C with an Award BIOS (I dumped this BIOS and submitted it to the retroweb guys, they only have an AMI BIOS for this board on the site)
Intel 386 DX-33 PGA CPU
No NPU installed
Realtek RTVGA 3106
Normal 3.5" 1.44MB Floppy Drive

I only have two I/O cards to try:

1. Multibest Systems MBCT02 - Pictured
2. A DTK PTI227W (https://theretroweb.com/expansioncards/s/dtk-pti-227w)

I have a couple of CF cards

1. An old Sankdisk 256MB card
2. A new Sandisk Ultra II 4GB card
3. An old Unigen 128MB industrial card
4. A new Verbatim 2GB card

When the Multibest I/O card is installed there are no video artifacts with any of the CF cards.
When the PTI1227 I/O card is installed the video artifacts seen in the image appear only with the Verbatim 2GB card. These artifacts are mostly visible after DOS loads but can appear in the CMOS setup screen as well, particularity on "warm boots" after the first cold boot.

-Replacing the video card with a trident one changes nothing.
-Replacing the DRAM in the realtek card with known good DRAM chips changes nothing.
-Swapping the award BIOS for the AMI one on the retroweb changes nothing.
-Changing the base I/O for the IDE controller from primary to secondary changes nothing.
-Disabling IRQ usage on the video card changes nothing.
-Removing the "DMA" jumper on the IDE to CF card adapter changes nothing.

While the system appears to run perfectly fine both with and without the artifacts, I just would like to know what's most likely going on here with the winbond based i/o card and that Verbatim CF card.

Thanks!