Does the adapter board have its own WT/WB settings or are those settings simply passed through from the underlying motherboard? I sense some inconsistency there.

It is weird that in the video, the Am486DX4-100 is printed as a 486DX2-100.

This BIOS is not compressed and I don't see any code to intentionally lock out Intel DX4s and I don't think that would make sense as it would probably cost extra money to get Award to produce such a BIOS. Further, it runs in PCem using either CPU, but I'm not sure how thoroughly PCem distinguishes these in its behavior. But I do think there is a problem in the CPU detection table at 7354h. The first field is a set of flags I haven't investigated further, the second is the minimum DX-at-reset value for that class of processor, and the third is the maximum.

Notice for the DX4 WB the stepping is hardcoded as zero (490h-490h) rather than being ignored as it should be (490h-49fh). I think this means the Am486DX4 is not considered a DX4 WB, while your i486DX4 &EW is detected as one, and the misdetection cancels out whatever WT/WB issue is going on with your board.

It is also weird that this board apparently supports DX4 WB, or at least the BIOS attempts to detect one, but doesn't support the P24D aka DX2-WB with DX=x47xh. Usually it is the other way around.
It's also possible that the board shipped from the factory wired wrong to support 486 WB CPUs. You can read a bit more about that here. Note your Enhanced Am486DX4-100 would exhibit the same L1 WB issues as the Am5x86: http://web.archive.org/web/20220407063508/htt … ink/amd5x86.htm

Hi Justin and Jake,

Intrigued by this Intel DX4 issue, I have been looking in the EXP4044VL Rev. 2.1 BIOS code as well.
What I found was a regular code base for an Award 09/1994 BIOS with CPU support for all 486 models of that era. This includes support for the iDX4-100.

However, L1 cache WB mode in this BIOS is only supported for the Intel 486DX2-WB (P24D) and for Cyrix design 486DX/DX2 models. So the Intel 486DX4 &EW and Enhanced Am486DX2/DX4/Am5x86 are only supported when set to L1 cache WT mode.

I believe the 486DX4ODP comes in WT versions only and should run without issue with this BIOS.
Seeing your video, I think there must be something else wrong with this board.

About the curious “For best performance we recommend the Am486 microprocessor” indication on this motherboard, I think this has something to do with this being a VLB board.
Because the VLB is coupled to the FSB of the CPU, running the VLB and FSB at 40MHz gives a better performance than 33MHz when using VLB cards instead of ISA.
After the i486DX-40, Intel stayed with 33MHz FSB on their 486DX2-66 and DX4-100. But AMD went further with their Am486DX-80 and Am486DX4-120, running on a 40MHz FSB!
Or DataExpert had a commercial interest in AMD? Just speculating. 😉

Anyway, I find it hard to believe that this silkscreened Am486 recommendation means that the board has trouble running CPUs from the leading manufacturer…

@jakethompson1, over the years I did some detailed analysis on 1994 and 1995 Award socket 3 BIOSes and I agree with your view on the CPU Reset_ID table in this Rev. 2.1 BIOS.
Only the third table item, 0490h-0490h, is for the Cx486DX and not the DX4-WB. 😉
If you like to read what I discovered about the CPU type detection in these Award BIOSes, check-out my DIY BIOS Modding guide at: Re: Diy modding support for k6+And 120gb hard drives into bios roms

It is true that the Reset_ID table doesn’t contain a dedicated 047xh item for the P24D. But this BIOS has a separate routine with hardcoded CPUID ‘GenuineIntel’ instructions to detect this i486DX2-WB. It is the only place in this BIOS where CPUID is used.
In addition, separate code is used to detect Cyrix design CPUs (DIV 5/2 method).

Cheers, Jan

Edit: In my e-mail archive I found correspondence with another EXP4044VL user who successfully used the latest BIOS from another OPTi 82C895 board to run his Am5x86 in WB mode.
He used the Edom/Wintech MV035 Rev.F Award BIOS and this one is available for download from https://theretroweb.com/motherboards/s/edom-w … rev.f#downloads
This 11/17/95-OPTI-802G-2C4UKW01-00 BIOS supports all WB capable Socket 3 CPUs, including the Am5x86 in x4 mode, and has a fix for the 2GB Harddisk display limit bug for full 8GiB IDE support.