First success!

1) AMD 5x86-133 initialized with default BIOS 4.27 setting

2) AMD 5x86-133 initialized as 486DX2-66 subroutine in BIOS 4.27

BIOS 4.27GN2 patched for the max performance of AMD 5x86-133 and nice CPU POST string.

Hi, all.

Please check the latest bios modifications for vip-io.

Tnx!

Hi, Babasha.

Please check the chipset utility for vip-io/io2.

Hi, Babasha.

Results of using the tuning utility are below.

Pci perforformance before and after

Yftul wrote on 2025-05-08, 17:43:

Pci perforformance before and after

So that indicares that performance got better?

Correct

Yftul wrote on 2025-05-10, 16:45:

Correct

I’ve got 486 VIP without the IO that I bought new a long long time ago. https://theretroweb.com/motherboards/s/fic-486-vip

I’ve spent years looking for a BIOS that will have good PCI performance and properly recognize an AMD133. Can’t wait to try out the bios. But I’ll have to wait until wednesday at least because I got a lot of stuff going on right now.

Sure. Please try it. Possibly you will need to use your own values for RX22 and RX51 registers, corresponds to the possibilities of your hardware.

PS. I used this datasheets for my experiments
https://dosdays.co.uk/media/via/VIA_82C496G.pdf
https://theretroweb.com/chip/documentation/vt … f6889725501.pdf
actually vip-io contains chipset 82486+82505, but seems it at least partially compatible with 496.

Yftul wrote on 2025-05-12, 11:21:

Sure. Please try it. Possibly you will need to use your own values for RX22 and RX51 registers, corresponds to the possibilities of your hardware.

The BIOS identifies my CPU as "Am486DX4B-S CPU at 150MHz". Mostly. Every so often I get "Am486DX4B-S CPU at 120MHz". It's an AMD X5-133 ADZ

Speedsys sees it as 133Mhz with a CPU score of 44. VESA video write speed in 16MB/s

Edit - Doom Frame rates are similar when using comparable PCI and VLB cards. About 74 FPS. So the PCI is performing well. The problem is that when I use a PCI video card, the ATA storage performance becomes very poor and occasionally fails completely.

You have a multiplier coefficient of 3 set, so the 5x86 processor support modification code is not activated.
As for the PCI performance speed—what kind of card is it, and how was the speed measured? DrHard, for relatively modern graphics cards (such as the Tseng et4000/w32p, S3 Trio64V+, S3 Virge), reports speeds of around 30 MB/s and higher. However, since your bus runs at 50 MHz, the PCI frequency is divided by 2. This could potentially be a factor.
Regarding ATA, these drives are highly sensitive to overclocking. Try replacing the drive with a CF card and see if you experience any speed drops with it.