Afraid I can't answer the main questions, but can chime in that my Spring Circle So5 VLB board with Forex chipset (which I slightly suspect of being a relabeled OPTi 571) also doesn't play nice with non-P54 CPUs. Tried Cyrix 6x86 and it refused to boot, same with an otherwise very tolerant P55C. I actually had an interposer I intended to try later low-voltage things on, but I managed to kill a few essential pins on them, so that plan failed. I am expecting a K5-PR166 in a week or two, wil try that and will also see about doing a BF1 mod on a P200 (non-MMX) that runs fine on the board at 100MHz.

Funnily enough, shortly after I've found this thread, I found a decent deal for a Pentium 166 Overdrive. Not cheap, and it's pretty much the most pointless Overdrive in history, but it costs okay compared to the other options, and I'm pretty sure it will work. I think this should scratch my itch for upgrading this board and allow me to patiently wait for a good deal on a CPU interposer 😀

It remains to be seen whether P166 will actually be able to produce 30FPS in Quake on this system given that the chipset is quite a bit slower even than an Intel 430FX. However, a Pentium 100, with proper RAM and cache timings gives me about 24FPS in vanilla patched version of Quake and 27 FPS in QDOS (surprisingly, it's quite a bit faster than vanilla version).

In the meantime I think I'd like to try and find the disks for Evergreen Spectra with MR BIOS files. Versions 3 and 4 don't have anything for the Opti chipset, but they are meant to support AMD K6-2/3. Maybe earlier versions could have the files I need?

If it’s a 100 cpu is that 66x1.5 or 50x2?

If that’s 50mhz x 2 I wonder if you couldn’t run a k6 2+ in it at 2x=6x multiplier and use a jan bios patch?

It’s weird you say non intel cpus don’t work in it? Do they literally not post?

There is always tillamook... apparently there is a pin mod to make it force 4x multiplier check out the tillamook running with cache thread.

Sphere478 wrote on 2021-03-05, 15:40:

If it’s a 100 cpu is that 66x1.5 or 50x2? […]
Show full quote

If it’s a 100 cpu is that 66x1.5 or 50x2?

If that’s 50mhz x 2 I wonder if you couldn’t run a k6 2+ in it at 2x=6x multiplier and use a jan bios patch?

It’s weird you say non intel cpus don’t work in it? Do they literally not post?

There is always tillamook... apparently there is a pin mod to make it force 4x multiplier check out the tillamook running with cache thread.

It's 1.5x66. The only multiplier this motherboard has is 1.5, you can only switch FSB between 60 and 66.

Non-Intel CPUs don't post at all, yes. MMX was actually the same before I tried the Award BIOS from HOT-543 — which leads me to believe it's a BIOS limitation, not a hardware one. This board was in fact released in 1994, a year before AMD K5 was introduced. However, I don't think I've ever heard about CPU checks in BIOS on a Socket5/7 motherboard (outside of Intel motherboards, that is).

I suppose you mean Jan's patch to add K62/3+ support? I don't see any motherboards with Opti596/597 on the list, but I'll have to take a closer look later. But I kind of always assumed those patches were for Soc7 chipsets only, not for earlier Soc5 stuff.

jheronimus wrote on 2021-03-05, 15:49:

It's 1.5x66. The only multiplier this motherboard has is 1.5, you can only switch FSB between 50 and 66. […]
Show full quote

Sphere478 wrote on 2021-03-05, 15:40:

If it’s a 100 cpu is that 66x1.5 or 50x2? […]
Show full quote

If it’s a 100 cpu is that 66x1.5 or 50x2?

If that’s 50mhz x 2 I wonder if you couldn’t run a k6 2+ in it at 2x=6x multiplier and use a jan bios patch?

It’s weird you say non intel cpus don’t work in it? Do they literally not post?

There is always tillamook... apparently there is a pin mod to make it force 4x multiplier check out the tillamook running with cache thread.

It's 1.5x66. The only multiplier this motherboard has is 1.5, you can only switch FSB between 50 and 66.

Non-Intel CPUs don't post at all, yes. MMX was actually the same before I tried the Award BIOS from HOT-543 — which leads me to believe it's a BIOS limitation, not a hardware one. This board was in fact released in 1994, a year before AMD K5 was introduced. However, I don't think I've ever heard about CPU checks in BIOS on a Socket5/7 motherboard (outside of Intel motherboards, that is).

I suppose you mean Jan's patch to add K62/3+ support? I don't see any motherboards with Opti596/597 on the list, but I'll have to take a closer look later. But I kind of always assumed those patches were for Soc7 chipsets only, not for earlier Soc5 stuff.

In that case I think a tillamook on a upgrade adapter is your best bet

Btw, the adapters themselves have multiplier jumpers I almost forgot so your 1.5x shouldn’t be an issue anymore.

However,

A 233mmx will interpret the 1.5x as 3.5x so that is another good option to get to 233.

But since you are getting a upgrade adapter may as well try a tillamook for an extra 33mhz🤷‍♂️

Tillamook 266MHz and working L2 cache?

I would be running tillamooks myself if they hadn’t disabled the smp on them. Ugh..

Well, damn. Pentium Overdrive 166 didn't start on this board. I'll have to check it on a proper Socket 7 board to see if the chip is actually alive, but it all seems pretty weird. I mean, why would regular Pentium 166 work (although at 100MHz), but an Overdrive (non-MMX) won't?

Is the P166@100 running at 1.5x66? I don't know much about your specific overdrive, but sometimes overdrives were stripped or certain features supported in the standard version. The DX4 overdrive doesn't support 2x multiplier, while a regular DX4 does (for example).

Anonymous Coward wrote on 2021-03-26, 15:57:

Is the P166@100 running at 1.5x66? I don't know much about your specific overdrive, but sometimes overdrives were stripped or certain features supported in the standard version. The DX4 overdrive doesn't support 2x multiplier, while a regular DX4 does (for example).

Yes, the motherboard only supports 1.5x.

I thought Overdrives had locked multipliers that overrode the motherboard settings? I think I've read somewhere that the whole point of this P-166 Overdrive is to upgrade the Socket 5 motherboards that don't support higher multipliers.

I guess.

There are some Socket5 motherboards that support multipliers. I wasn't sure if yours did or not, so I guess that's not an issue.

So, I've actually made a mistake — this was an MMX Overdrive after all, a SL24W. The original BIOS did not start with MMX chips, hence it did not work with this one. I've flashed a BIOS from TMC PCI54PV and the system started:

And Quake did deliver 33 FPS using somewhat tweaked cache and RAM settings and a QDOS sourceport. The vanilla Quake crashes though.

woohoo!!! good job. any effects from using the different bios?

Sphere478 wrote on 2021-03-31, 00:09:

woohoo!!! good job. any effects from using the different bios?

I'll do some testing on weekend, but I've already mentioned vanilla Quake crashing on this setup. Also UNIVBE decided to re-run configuration at startup that froze the system. Running Windows 95 would probably be the ultimate test of the system stability, but I don't have it installed ATM.

What about contacting Jan?

Sphere478 wrote on 2021-03-31, 05:29:

What about contacting Jan?

Well, it certainly wouldn't hurt. Sent him an email.

There are now some good (and cheap) options for adjusting multipliers on these old socket 5/7 boards. I've been hard at work. 🤣

Socket 5/7/SS7 (Motherboard) Tweaker (Released)