The CPU doesn’t really care about the FSB that’s more of a motherboard overclocking thing if you adjust the multiplier to a core speed that is appropriate for what the CPU can handle you will do fine

If your CPU is 2.2 V cyrix, then you have the 4X multiplier you would just have to enable it

But if you are running 100 MHz front side bus 400 MHz probably is not going to be stable

The best you can hope for on a 2.2 V cyrix is probably 350 MHz

Re: Cyrix 400gp multiplier settings

Sphere478 wrote on 2025-10-22, 04:01:

The CPU doesn’t really care about the FSB that’s more of a motherboard overclocking thing if you adjust the multiplier to a core […]
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The CPU doesn’t really care about the FSB that’s more of a motherboard overclocking thing if you adjust the multiplier to a core speed that is appropriate for what the CPU can handle you will do fine

If your CPU is 2.2 V cyrix, then you have the 4X multiplier you would just have to enable it

But if you are running 100 MHz front side bus 400 MHz probably is not going to be stable

The best you can hope for on a 2.2 V cyrix is probably 350 MHz

Re: Cyrix 400gp multiplier settings

Thanks a lot
Unfortunately I don't have a 2.2V MII CPU, but only the 2.9V ones, in particular the 333 is the fastest I have.
Thanks to Jan who provided me with a correct BIOS, CPU 333 can also use the 4X 66 setting, instead of the original 3.5X 75, so 266 MHz instead of 263.
Unfortunately today 2.2V MIIs are expensive, in the past instead when they were cheap, you could buy an assorted batch, in which there were some 2.2V copies, today I don't think it's possible.
I was asking about the FSB above 100, to know if it would create problems, basically if you don't exceed the factory frequency, everything should work without problems, at least hopefully.
Jan's correct BIOS, I needed it for my ACORP A-5VIA3P (VIA VPX) PC, after turning it on I had problems with the drive and stability, the PC crashes shortly after loading MS-DOS 5.00.
I performed some tests at lower frequencies, and at 233 MHz it's fine, with multi 4X I tried at 240 MHz, and it works but some programs have problems, and maybe the PC crash takes longer.
Maybe it could be a problem of linear regulators, which heat up too much, or it could be a problem of VCORE, slightly lower, there is no 2.9V but only 2.8V.

Your best luck finding a 2.2V Cyrix MII is with one of the silver tops, like this: https://www.chipdb.org/img-cyrix-miiv-333gp-greytop-591.htm There was an abundance of these CPUs about 8 years back on eBay. They sold for $20-25.

As for FSB, I run my MII at 3.5 x 95 MHz because 3.5 x 100 wasn't quite stable on the motherboard I wanted to use. Plus, 3.5 x 95 was faster than 3 x 100. Enable some of the Cyrix register settings, pair it with a 3dfx Voodoo, and you'll have an acceptable pre-millennium gaming system.

I haven't come across an in-depth analysis to determine whether a Cyrix 6x86MX or MII rated for 66 MHz FSB is fully stable at 100+ MHz FSB. I find it peculiar that Cyrix would rate their MII-333 chips at 3x83 MHz rather than 2.5x100 MHz. It suggests to me that there was some aspect of their qualification tests which didn't like 100 MHz.

feipoa wrote on 2025-10-22, 09:07:

Your best luck finding a 2.2V Cyrix MII is with one of the silver tops, like this: https://www.chipdb.org/img-cyrix-miiv-333gp-greytop-591.htm There was an abundance of these CPUs about 8 years back on eBay. They sold for $20-25.

As for FSB, I run my MII at 3.5 x 95 MHz because 3.5 x 100 wasn't quite stable on the motherboard I wanted to use. Plus, 3.5 x 95 was faster than 3 x 100. Enable some of the Cyrix register settings, pair it with a 3dfx Voodoo, and you'll have an acceptable pre-millennium gaming system.

I haven't come across an in-depth analysis to determine whether a Cyrix 6x86MX or MII rated for 66 MHz FSB is fully stable at 100+ MHz FSB. I find it peculiar that Cyrix would rate their MII-333 chips at 3x83 MHz rather than 2.5x100 MHz. It suggests to me that there was some aspect of their qualification tests which didn't like 100 MHz.

Thank you very much, yes I wanted to buy one of the silver ones, from memory I don't remember if it was a 2.2V, but they were in high demand, I also have one of the black ones, a MII 300, I don't think it's different from the gold ones, in the collection I have almost everything Cyrix, except for some 6X86 or 6X86L from IBM.
Interesting this thing on the MII with FSB 95, faster than the 100 one, some ASUS motherboards for example, they also have an FSB 97, I don't know if it would be worth trying, of course at most they are about 8 MHz more, but who knows if it's okay.
In fact, it's strange, but on the Internet I saw that faster versions had to come out, including MII 466 500 533, I think they reach 350 MHz, unfortunately they didn't arrive on the market, maybe VIA chose the Cyrix III, and left the S.7 preferring the S.370, but I think that without an integrated L2 cache, it was even slower than Celeron equivalents.
I don't have the Cyrix III, while I have a pair of VIA C6, I tried a 600 MHz one, it totally disappointed me, it goes roughly like a 200 MHz (or a little more), the IDT derivation of this CPU, makes me think that the IDT Winchip 200, also goes slow.