[edit: paragraph removed. I had the Klamath voltage wrong and that undermines the rest of what it said.]

I would think that at least well supported 440FX boards would have had BIOS updates to add support for some later 66FSB CPUs including the Celerons, but I've never had a 440FX slot-1. I'm not aware of any technical reason it couldn't run them. However if they didn't sell well and got discontinued quickly enough then maybe the manufacturers didn't put much effort into updating them.

Interesting and never gave any thought to it even though I own a dual slot Tyan board with this chipset.

computergeek92 wrote:

Are the 440FX Pentium II boards able to be used with slot to socket converters with Mendocino Celerons or possibly the higher clocked 66FSB Coppermines? Are there modded BIOS availiable for certain boards? All Pentium II's ran at 2V, and so did the Mendocino Celerons. Would the normal slot 1 Celerons like the 400MHz model work too? Mendocinos may be my best bet due to older boards like this might be even less compatible with later Celerons. I read that 440LX boards had much more support for Celerons, but I don't generally take no for an answer. . .

Klamath ran with a CPU Vcore of 2.8v, while Deschutes and the Katmai Pentium II+ (lol) ran with about 2.0v (might be some slight upping of the VCore with the upper variants of a CPU family, before usually a die shrink).

No doubt boards made by Intel should be a decently stable choice if considering slockets and it would be interesting how well the simm ram in a 440FX board would cope with faster Pentium II's or the faster Celerons. These boards didn’t even have UDMA, APM, or AGP support.