Such motherboards use jumpers, in most cases. Lowest I could go was 2 x 66, on a BX board. Few slot 1 boards go below 66 MHz FSB, perhaps some LX models.

Downclocking a P2 is not great, IMHO. They can't go low enough through multi / fsb or they are too slow when disabling L1 cache.

I have two of those CPUs, hoping I could build 1 system to cover both older, speed sensitive dos games and newer ones - did not work in practice

yep both my 440bx boards can only go as low as 2x66mhz fsb - 133mhz was the slowest i got my klamath 266mhz down to. it was good enough for lucasarts adventures and jazz jackrabbit. didnt test 386 era games. by all means if you already have the hardware, have a go and let us know if you find anything special.

Joakim wrote on 2021-11-11, 20:16:

We were discussing underclocking of Pentium 2. It seems likely that Pentium 2 <333 MHz made before week 34 1998 are unlocked.
I was interested in examples of slot 1 motherboards that can set the multiplier and fsb in bios and how far you can go. Maybe even 1x50mhz is possible?

There are early 440BX motherboards that can go as low as 50MHz but it depends on the frequency generator that is installed. My ASUS P2B-S rev. 1.03 has an ICS 9150-08 that covers 50MHz through 112MHz.
I don't think that multipliers can be set to lower than 2x but I may be mistaken.

Maybe even 1x50mhz is possible?

Minimal multiplier for P6 is 2x.

It seems likely that Pentium 2 <333 MHz made before week 34 1998 are unlocked.

Deschutes also had 300 Mhz model.

foil_fresh wrote on 2021-11-11, 23:08:

yep both my 440bx boards can only go as low as 2x66mhz fsb - 133mhz was the slowest i got my klamath 266mhz down to. it was good enough for lucasarts adventures and jazz jackrabbit. didnt test 386 era games. by all means if you already have the hardware, have a go and let us know if you find anything special.

This is kind of what I was looking for, alternative to the AMD K6-2+ speed throttling thing. For me it would be ok to set such things in bios and reboot but opening up the computer and set the jumpers is a little bit too much of a hassle. I don't have a pnp board or a unlocked Pentium 2 yet but maybe I will get one and would like to know my alternatives.

Two old threads on the subject:
Pentium 2 @ 133 mhz project ,done

Re: Slot 1 motherboard cappable of doing FSB below 66 MHz?

Joakim wrote on 2021-11-11, 20:16:

We were discussing underclocking of Pentium 2. It seems likely that Pentium 2 <333 MHz made before week 34 1998 are unlocked.

I was interested in examples of slot 1 motherboards that can set the multiplier and fsb in bios and how far you can go. Maybe even 1x50mhz is possible?

Some 333MHz and 400MHz Pentium 2s were also unlocked. These were Deschutes and not Klamaths

You can find some more info here: Which Pentium IIs can be underclocked?
and here: Slowing a 440BX based PC

Tetrium wrote on 2021-11-13, 17:30:

You can find some more info here: Which Pentium IIs can be underclocked?
and here: Slowing a 440BX based PC

Regarding the Pentium II: I made a summery listing like seven years after these discussions, in 2017. It is in the 5th post of this topic. Click "show full quote".
Downclocking intel cpu help?
That is the CPU, the motherboard is another subject.

Thanks for the replies. My slowest board is the MS6119 and it is supposed to go down to 2x66 MHz, but I looked quickly and could not find jumpers 5-6 on the board which is strange. The board lacks some fan headers as well so it might be a non standard OEM version or something.

I also recently aquired a Epox bx3 which has very nice self explanatory jumpers, but it only goes down to 4x 66.

I read something here that if you run a very low clock you wont be able to use L2 or something like that. Maybe it makes the set up too slow.

But atm I neither have an unlocked P2 or a motherboard that can set multipliers. Finding a CPU is quite easy but the motherboard, I'm not even sure it exists. The ASUS P2B-S seems to be your best bet but it seems to have jumpers. It might be possible to connect a turbo switch to it I guess.

An alternative would be to go with a low multiplier Pentium 3 or something and just lower the fsb to 50 and get something like 200 mhz but I guess it is too fast to be useful.

foil_fresh wrote on 2021-11-11, 23:08:

yep both my 440bx boards can only go as low as 2x66mhz fsb - 133mhz was the slowest i got my klamath 266mhz down to. it was good enough for lucasarts adventures and jazz jackrabbit. didnt test 386 era games. by all means if you already have the hardware, have a go and let us know if you find anything special.

Could you please provide these board names/model no? I am searching to get a 440BX board which supports 2x multiplier. Thanks

Abit had the Soft Menu BIOS thing going on, so I think the LX6 would let you change multi without physically fiddling the jumpers.

If flexibility is what you're interested in, then the best Pentium 2 (actually, even faster than a Pentium 2 when overclocked @ FSB 133) is a VIA Ezra-T @ 1 GHz. 😁

stealthjoe wrote on 2021-11-19, 08:51:

Could you please provide these board names/model no? I am searching to get a 440BX board which supports 2x multiplier. Thanks

440bx ASUS boards of the P2B(..) and P3B(..) series all have 2x multi options via jumpers as far as I know.

stealthjoe wrote on 2021-11-19, 08:51:

foil_fresh wrote on 2021-11-11, 23:08:

yep both my 440bx boards can only go as low as 2x66mhz fsb - 133mhz was the slowest i got my klamath 266mhz down to. it was good enough for lucasarts adventures and jazz jackrabbit. didnt test 386 era games. by all means if you already have the hardware, have a go and let us know if you find anything special.

Could you please provide these board names/model no? I am searching to get a 440BX board which supports 2x multiplier. Thanks

Chaintech 6BTM also supports 2x multiplier.

bloodem wrote on 2021-11-19, 14:54:

If flexibility is what you're interested in, then the best Pentium 2 (actually, even faster than a Pentium 2 when overclocked @ FSB 133) is a VIA Ezra-T @ 1 GHz. 😁

I'm not familiar with it, is it the cyrix equivilabtvto P2? Saw a setting in one of my motherboards for cyrix..

<- I am quite a fan.

Joakim wrote on 2021-11-11, 20:16:

We were discussing underclocking of Pentium 2. It seems likely that Pentium 2 <333 MHz made before week 34 1998 are unlocked.

I was interested in examples of slot 1 motherboards that can set the multiplier and fsb in bios and how far you can go. Maybe even 1x50mhz is possible?

Most flexible CPU in a Slot 1 is a VIA C3 Ezra-T overclocked to 1200 MHz. Has smooth scaling range without the gaps found in the VIA C3 Nehemiah. There are some posts around here with a Gigabyte motherboards FSB and CPU registers/ cache being controlled via software in DOS for slowdown. No need to open up case.

Even then, using simple switches to control dip-switches and headers is fairly trivial for motherboards without full BIOS control.

Another alternative is using an unlocked P2 and a motherboard that can force Write-Thru cache instead of Write-Back cache on a P2. This can get you smoother CPU scaling, filling in gaps around a fast 386/ 486 by manipulating other parameters. I think I posted something about this on the forum ages ago.

Just looking at the manual for an abit be6-II and it lists a 1.5x multiplier.
Though, I have no idea which, if any cpu supports this.
Thought I'd mention it since everyone here lists 2x as the lowest possible multiplier

enjoy !

stealthjoe wrote on 2021-11-19, 08:51:

foil_fresh wrote on 2021-11-11, 23:08:

yep both my 440bx boards can only go as low as 2x66mhz fsb - 133mhz was the slowest i got my klamath 266mhz down to. it was good enough for lucasarts adventures and jazz jackrabbit. didnt test 386 era games. by all means if you already have the hardware, have a go and let us know if you find anything special.

Could you please provide these board names/model no? I am searching to get a 440BX board which supports 2x multiplier. Thanks

Asus P2b and LuckyStar 6abx2v. The Asus needs jumpers to set multi yet the Lucky star can change all settings in BIOS.

weedeewee wrote on 2021-11-20, 17:36:

Just looking at the manual for an abit be6-II and it lists a 1.5x multiplier.
Though, I have no idea which, if any cpu supports this.
Thought I'd mention it since everyone here lists 2x as the lowest possible multiplier

Maybe some exotic test sample once did 1.5x multiplier in an Abit lab. But normal Pentium IIs cannot do that, 2x is the lowest.