Ok that would be a switch (just like a jumper) for your purpose. I doubt you should ever switch speeds while it is on, based on the fact it is made for a jumper. It is not like the turbo switch on XT, 286 and some 386. Any old full size AT case with a turbo switch should work. No do not have a board with that exact jumper but have some old boards with OC override capabilty.

i've seen people hook multiplier jumpers up to turbo swtiches which can be changed on the fly without hazard (but it doesn't actually use the chosen multiplier until the next boot when the pins are actually in effect) so im just wondering if it's an instant fsb change or next boot type situation.

the cpu arrives in ~3 weeks so i'll just have to test it when it gets here. its not a massive game changer if the turbo66 jumper works or not because the bios is fairly capable.

IIRC, the CPU only checks the 66/100MHz pin at boot-time, so probably won't be able to change speed on the fly, without a reset ..

H3nrik V! wrote on 2020-03-11, 12:13:

IIRC, the CPU only checks the 66/100MHz pin at boot-time, so probably won't be able to change speed on the fly, without a reset ..

That check has nothing to do with the speed it runs at. That's just the lock and it will refuse to run if locked and wrong FSB speed is used.

Switching FSB speed on-the-fly normally works fine. I've built two systems with such a switch and there are no issues.

That header, however, is not meant for non-factory use. It may not work when switched on-the-fly (or not at all).

derSammler wrote on 2020-03-11, 12:18:

That check has nothing to do with the speed it runs at. That's just the lock and it will refuse to run if locked and wrong FSB s […]
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H3nrik V! wrote on 2020-03-11, 12:13:

IIRC, the CPU only checks the 66/100MHz pin at boot-time, so probably won't be able to change speed on the fly, without a reset ..

That check has nothing to do with the speed it runs at. That's just the lock and it will refuse to run if locked and wrong FSB speed is used.

Switching FSB speed on-the-fly normally works fine. I've built two systems with such a switch and there are no issues.

That header, however, is not meant for non-factory use. It may not work when switched on-the-fly (or not at all).

Yeah, on second thoughts, it's only the multiplier pins, that are read at boot time only, as the multiplier is the CPU's function, and the FSB is the board's

derSammler wrote on 2020-03-11, 12:18:

Switching FSB speed on-the-fly normally works fine. I've built two systems with such a switch and there are no issues.

That header, however, is not meant for non-factory use. It may not work when switched on-the-fly (or not at all).

if you dont mind me asking, what kind of systems and how were they set up? does it actually change FSB instantly? thanks

Sure, these two:
Flytech Carry-1 S370-based mini PC (2001)
AMD 5x86 X5-133 (now with POD)

//edit:
Three, actually. Forgot this one:
My Intel Plato/Premiere II build

In all cases, one jumper for FSB speed is connected to a toggle switch.

ok thats great, i'm really hyped to try this turbo header to see how it works. btw nice and strong little p3 system!

I suspect its the B21 trick it uses:
http://www.thg.ru/cpu/19980514/print.html
Quite common on motherboards aimed at enthusiasts.
Most if not all P2's were "vulnerable" to this until Intel realized ppl even used it in servers and sorted it in the CPU's.

thanks for the link, will give it a read