Good job ! Wonder why DFI went back to a VIA 82C486 in the VPP after using 82C496 in the VPA, VPB, VPC, etc

Horun wrote on 2022-05-30, 04:08:

Good job ! Wonder why DFI went back to a VIA 82C486 in the VPP after using 82C496 in the VPA, VPB, VPC, etc

Maybe because this one has no IDE and FDD controller onboard. While testing it never showed ‚No Floppy’ error, so that’s why I guess.

Hi maksymke,

Welcome to the Vogons community.
That’s an interesting early 486 VLB board with PCI slots. 😀

Did you check the actual Am486DX4-100 speed with a DOS tool? The early to mid 1994 BIOSes on these boards don’t support the Am486DX4 CPU (that’s why they are detected as 80486DX2) and may report the wrong speed as well.
You can use my Chkcpu DOS utility to get an accurate speed reading.
Follow the CPU Identification utility link in my signature and download ckcpu126.zip.

The latest BIOS for this board from https://www.ultimateretro.net/nl/motherboards/10089 is the Award
10/24/94-VT82C505-2A4L4000 BIOS. Is this the BIOS you are running?

I’ve checked this BIOS for CPU support and it has indeed no Am486DX4 NV8T support. But the Intel DX4 is supported, so an Enhanced Am486DX4 SV8B should work when set to L1 cache Write-Trough mode. It behaves exactly like a DX4 then. The same goes for an Am5x86-133 when set to x3 multiplier and L1 cache WT modes.

Greetings from Holland,
Jan

Chkcpu wrote on 2022-05-30, 15:00:

(...) Did you check the actual Am486DX4-100 speed with a DOS tool? The early to mid 1994 BIOSes on these boards don’t support th […]
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(...)
Did you check the actual Am486DX4-100 speed with a DOS tool? The early to mid 1994 BIOSes on these boards don’t support the Am486DX4 CPU (that’s why they are detected as 80486DX2) and may report the wrong speed as well.
You can use my Chkcpu DOS utility to get an accurate speed reading.
Follow the CPU Identification utility link in my signature and download ckcpu126.zip.

The latest BIOS for this board from https://www.ultimateretro.net/nl/motherboards/10089 is the Award
10/24/94-VT82C505-2A4L4000 BIOS. Is this the BIOS you are running?

I’ve checked this BIOS for CPU support and it has indeed no Am486DX4 NV8T support. But the Intel DX4 is supported, so an Enhanced Am486DX4 SV8B should work when set to L1 cache Write-Trough mode.
(...)

THANK YOU
I think, we're getting somewhere right now. I'm not a BIOS specialist by no means and you have provided very valuable knowledge.

Yes, this BIOS is exactly 10/24/94-VT82C505-2A4L400-20, so it figures why the AMD NV8T won't work.
L1 cache set to write-through. Check.

Running your CPU utility with the AMD SV8B recognized in BIOS as '80486 DX2 80MHz' did show that it runs @ 100MHz, but the CPU model is " 'classic' 486 ", so yeah, no full support for late 486 AMDs on this board, even though it works as it should.
Same test with the CPU changed in BIOS to '80486 DX2 66MHz' (I just switched JRN1 to CYRIX, no other jumpers were moved) - it will actually run @ 66MHz. Very interesting, but again - I don't really know how I'm affecting these changes fiddling around the jumpers without the manual in front of me. Maybe the multiplier is being changed here, not the bus speed.

I also ran CHKCPU on my 'daily' 486:
MB - Biostar MB-8433UUD-A VER 3
CPU - AM5x86 133 @160MHz
And it recognized all CPU parameters providing much more details than on the DFI board, like the multiplier, manufacturer and the correct CPU ID - AM5x86-P75, even though BIOS on the Biostar detects it as the P90 when it's overclocked 133 -> 160MHz. Different boards different results. Does your utility depend on the BIOS to get the CPU IDs?

I'm really happy, again, with the results. And at the same time I'm kind of disappointed - I thought that board is a bit newer, maybe late 1995 instead of late 1994. With all the PCI slots IMO it should deal at least with all DX4s and not just merely being able to power up with the oldest one. A very fine piece of hardware but a bit more oldschool than I anticipated.
Windows 95? No problem, I ran it on a standard 486DX and on a 100 and 120MHz DX4s but there are far better options to run it on a 486 (like the Biostar mentioned above, or the HOT-433, which I also have and recommend). This board looks like the very high-end 486 option to run Win 3.11 or NT3.5, and 80-100MHz is going to be more than sufficient to do so. And I won't be surprised if it really was some kind of cheap office NT3.5 workhorse back in 1995, it makes perfect sense to me.
What do you guys think?

I agree with your “cheap office workhorse” assessment, using older but proven technology. 😉
And using a VT82C505 VLB-PCI bridge chip to implement PCI slots, creating a versatile VLB/PCI board but with a lower PCI performance than when using a dedicated PCI chipset like on your MB-8433UUD-A.

OK, you have the 10/24/94 BIOS and although the AMD 486DX4’s / 5x86 are not supported, both the Am486DX4 NV8T and Am486DX4 SV8B will run on this BIOS. The NV8T will be indicated as an 80486DX2 and the SV8B as a DX4, but this is just cosmetic.
But be aware that with the Am486DX4 NV8T the BIOS will assume that this CPU is running at 2x40 or 2x50 instead of the actual 3x33MHz and will program the chipset for a 40 or 50MHz FSB with more wait-states, decreasing performance. Just set the Cache and DRAM timing control options in the CHIPSET FEATURES SETUP menu as you would for a 33MHz FSB depending on the speed of your DRAM and Cache chips (Medium or Fast).

But for an Am5x86-133 to run properly in x4 multiplier mode, the BIOS needs to be patched. 😉
When you are curious how this can be done, check-out my (not yet finished) story:
Re: Diy modding support for k6+And 120gb hard drives into bios roms

No, my CHKCPU utility doesn’t use any BIOS data. It only probes the CPU to get its information.
I wrote CHKCPU to have an independent check on various jumper or BIOS settings for (FSB)speed, multiplier, and L1 cache enable/disable and mode selections.
CHKCPU gets a lot of its data by using the CPUID instruction on later 486 and Pentium class CPUs, or from Device Identification Registers on Cyrix design CPUs. But on non-Cyrix CPUs without CPUID support (all 386 and most 486), the information CHKCPU can provide is limited.
That’s why you see only ‘classic’ 486, the Internal CPU speed, Current CPU mode, Internal (L1) cache mode, and Size of the L1 cache (Verbose mode only) on the Am486DX4 NV8T.
The Am486DX4 SV8B does support the CPUID instruction, so on this CPU, CHKCPU can provide a lot more details.

Cheers, Jan