Chkcpu wrote on 2026-01-08, 10:15:

Hi Beerfloat, […]
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Beerfloat wrote on 2025-12-31, 08:53:

I'm also hoping to find/cobble together Pentium MMX and K6-2/3 BIOS support with a voltage interposer.

Hi Beerfloat,

The SF586 05/18/95 (VIP3A-ZS1) BIOS is already on my “to be patched” list and I expect to start working on it later this month.

Note that the CPU support in this BIOS is very limited. I only see Pentium (P54) and Cyrix 6x86 (M1) support. No Pentium MMX, Cx6x86MX, K5, K6, or Winchip C6/2 support.
So I don’t know yet if Pentium MMX and K6-2/III support can be added to such an old BIOS. But Winchip support should be possible.
I will know more when I’ve completed the disassembly and analysis of this BIOS.

I will keep you posted.
Cheers, Jan

Hi Jan,
Real happy to hear it. I believe one of the previous owners already used this with a WinChip C6 so that might work without specific BIOS support.
My hope is eventually getting a K6-III(+) 400 up as that might just be a lot of fun with VLB.

(Zoals altijd weer goed bezig Jan. We wachten eea met spanning af!)

Cheers Mike

Starting to consider that this Forex chipset may really be its own thing altogether.

Cloning or relabeling an Opti is one thing but different PCI vendor and device IDs? I reckon that's less likely

I see a retro "gonzo" (i.e., independently developed without the chip manufacturer's assistance; does not imply negative meanings like crude or poor build quality) VL-Bus S3 Trio64V+ running the graphics of the Forex Pentium chipset based computer.
I have seen that somewhere else on Vogons from while back.

Babasha wrote on 2026-01-03, 20:36:

I see your board on eBay twice(?) Last time in .bg seller list - there is no cache tag chip so l2 cache no go And early in .de […]
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Beerfloat wrote on 2026-01-03, 19:41:

My board arrived and I'll be playing around with it in the next few days. The previous owner soldered a BF0/BF1 mod switch onto it.
I'll have to take a closer look at these cache chips because other pictures I've seen use a different configuration.

I see your board on eBay twice(?)
Last time in .bg seller list - there is no cache tag chip so l2 cache no go
And early in .de seller list - he use it with 2mb l2 cache and set up with pentium 200mhz (non-mmx) and idt winchip 200mhz

Okay, this settles the Forex chipsets might be relabeled OPTi chipsets controversy I sort of raised.
I thought running lspci from Linux might be pretty hard today.
Nice to have a new PCI Vendor and Device IDs display utility program that is DOS based.
I think one version of a 486 Efar chipset was a relabeled OPTi 82C802 chipset.
Note that Efar was purchased by Standard Microsystems Corporation (SMC, later SMSC) according to an article from Microprocessor Report around 1995, and perhaps they had a hand in developing Victory-66 south bridge that can be used with Intel FW82443BX (440BX north bridge).

Beerfloat wrote on 2026-01-08, 16:41:

Starting to consider that this Forex chipset may really be its own thing altogether.

Cloning or relabeling an Opti is one thing but different PCI vendor and device IDs? I reckon that's less likely

draft of UNOFFICIAL user manual 😀

Babasha wrote on 2026-01-11, 14:44:

draft of UNOFFICIAL user manual 😀

Bangup job Babasha. Real nice work on this!

Notes, not in any way meant as criticism:
- Should note somewhere that it's not an official manual. It looks that good (though the sections on VLB controls and troubleshooting should tip the reader off)
- You could actually include the frequency table in manual? Even if it's tentative.
- Last page (Board Layout) still empty. It's a draft, right?

Hey, been spending time on and off trying to get my board to a state I'm happy with and thought I'd give an update. It hasn't been the most straightforward experience overall compared to other boards but it's finally DOS and Windows stable and even pleasant to use.

First of all, L2 write back cache as opposed to write through makes a TON of difference on this board. Doom goes from 24.04 to 35.51 fps. Quake from 10.1 to 19.2 fps. The general feel in Windows is much, much smoother. More on cache in a followup post.

We've seen that 2 SIMMs are a little faster than one (26.13 MB/s vs 24.65 in Speedsys, 31 vs 34 in cachechk), still hardly 64-bit access memory bus territory. But sadly, outside of DOS, I can't say I've seen a truly stable experience on this board with more than a single SIMM installed. I intend to test some more SIMMs eventually.

Worse, the SIMM slots called SLOT 1 and 2 (both on BANK 1) do not seem to be functional on my particular board. I believe I got at least one of them to work one time but not anymore. And that's too bad because I had hoped to test whether our special chipset supports main memory bank interleaving, something a bunch of chipsets at the time were implementing. Maybe something someone else feels like looking into.

I also had varying luck with videocard compatibility, though some of that is likely due to using an LCD screen.

Tseng ET4000/W32p (Diamond Stealth 32 VLB) is recognised as an ET4000 by Win98SE and the basic Microsoft driver does work. The preferred OEM 'ET4000/W32 VLB' and 'Ultimate Truecolor /XL' 'Enhanced' drivers cause an invisible mouse cursor (even with acceleration down one notch) so that's not really usable.

My Tseng ET4000/W32i cards cause freezes during non-P&P phase of detection. I guess I could cancel and install manually but I don't really want that in my system.

An ARK 1000VL does work but anything above 640x480 gives a black screen on my Eizo with latest 1.29 driver, while 1.07 had an image corruption issue. Also this card has relatively fuzzy image quality.

My known good S3-864 (Genoa Phantom 64) works with Win98SE's built in 'S3' driver but shows major display and mouse cursor corruption when the S3 OEM driver is loaded. Tried a bunch of things to no avail. Only seen on this motherboard so far.

My S3-Trio64 (Spea V7-Mirage-P64-VL) seems to work fine, as does my S3-Trio32 (miroCRYSTAL 12SD VL). The latter has slightly sharper output and the cards are very close outside of high res Windows work, so that's my card.

As for VLB IDE controllers, the VLB Promise 20630 (EIDE2300) seems to work fine all the way up to D:6 and M:8 (fastest PIO and DMA modes).
My Holtek VIO3B seems ok as well but my Gotek doesn't seem to come up quickly enough on first boot for it not to flag a floppy timeout.

I have yet to try any PCI cards but I'll look into performance there later. I reckon we're mostly here for the VLB.

While I'm waiting for more cache chips to fill the second bank I believe the below info may be interesting for reference.
I've been testing single bank only, the one closest to the memory slots, presumably bank 0.

In addition to the cache chips that came with the board, I tested the ubiquitous ISSI IS61C1024-15N and Winbond W241024AK-15 128Kb x 8 SRAM chips.
My board came without a tag chip and I tried a few. The tag chip can be the same speed rating as the other cache chips (I use 15ns everywhere).

Found configuration settings:
512KB single bank: JP10: 1-2, JP11: 2-3, JP12: Closed, JP13: 1-2, JP14: 1-2
512KB requires at least a DIP28 32Kb x 8 (32KB) or larger tag.

1024KB single bank: JP10: 1-2, JP11: 2-3, JP12: Closed, JP13: 2-3, JP14: 1-2
1024KB single bank seems to require at least a 64Kb x 8 (64KB) tag chip(!). Which means DIP32.
Try as I might, I could not get 1024KB single bank to work with any 32Kb x 8 tag. YMMV, be happy to hear about other people's experiences.

Also, 1024KB brings a complaint from CTCM16N and newer about cacheable memory being < 2MB, or less than main memory.
I reckon this may be a misdetection as zero adverse effects are observed. Speedsys, Windows and game scores continue to be great. Earlier versions of CTCM as well as cachechk do not note any issues.
I am somewhat certain that this is the proper 1024KB jumper setting. Because frankly, there are 162 possible combinations of these jumpers and I tried them.

And so I present for you some other combinations that work and appear stable:
512KB: JP10: 1-2, JP11: 1-2, JP12: Closed, JP13: 1-2, JP14: 1-2
512KB: JP10: Open, JP11: 1-2, JP12: Closed, JP13: 1-2, JP14: 1-2
512KB: JP10: Open, JP11: 2-3, JP12: Closed, JP13: 1-2, JP14: 1-2
512KB: JP10: 1-2, JP11: Open, JP12: Closed, JP13: 1-2, JP14: 1-2
512KB: JP10: Open, JP11: Open, JP12: Closed, JP13: 1-2, JP14: 1-2
512KB: JP10: 1-2, JP11: 2-3, JP12: Closed, JP13: Open, JP14: 1-2
256KB: JP10: Open, JP11: Open, JP12: Closed, JP13: Open, JP14: 1-2

Also boots but errors in one test or the other, not looked at it in detail:
128KB: JP10: Open, JP11: 1-2, JP12: Open, JP13: Open, JP14: 1-2
128KB: JP10: Open, JP11: Open, JP12: Open, JP13: Open, JP14: 1-2