Now this is a thread I can get into!
Good luck finding a PIII or PIV board that will undervolt.
I'm a big PIII Tualatin/Celeron Tualatin fan and feel that these are the perfect CPUs for quiet systems. They run really cool and are very low wattage. I've been wanting to try and run them undervolted. I've always used an Asus Tusl2-C MoBo for my PIII/Tualeron stuff, it's a great board. Very stable, good OCer and lots of features but it won't undervolt. Bummer.
I finally got ahold of a couple of Abit ST6's. These are pretty much considered the "Top-Dog" when it comes to PIII Tualatin/Celeron Tualatin OCing and they happen to be able to undervolt as well. With this board I'm running my PIII-S 1.4Ghz at 1.3V. Default Vcore is 1.45V so this is about a 10% reduction in Vcore. This runs 100% stable at 1.3v. I've stability tested it several times by running Prime95 for 24hr sessions with zero errors. The difference in the full-load temps between default Vcore and the lower Vcore is just about 6C! My max CPU temp under full Prime95 load at 1.3V runs about 43C, at default Vcore load temp is about 48-49C. Damn, pretty schweet, huh?
I'm quite certian that you could get similar results with a Tualatin Celeron running at lower Vcore too. I can run my 1.1A Tualeron at 133FSB (1.463Ghz) on default Vcore. Seems to me that it would run at default speed on much lower Vcore, right?
Rot's 'o Ruck finding an ST6 though. Like most Socket 370 I815 boards they're not made any more. They are not available new anywhere that I've seen for the last 4-6 months. You can occaisionally find a used one on egay but they're hideously expensive, usually well over $150.
Some 815 alternatives to look at (that are available new) might be the Soyo SY-TISU and the EPoX EP-3PTA. They are both overclockable but I can't find out if they undervolt.
Well, how about PIV stuff?
All these guys are getting 600+ mhz OCs at default Vcore, you'd think there'd be all kinds of headroom to run at stock speed + lower Vcore, right? Too bad you can't find out. I build a lot of PIV-based systems for people (it's my side-job) and have never found a Socket 478 board that will allow undervolting the CPU. Abit, Asus, EPoX, Gigabyte - no board that I've used from these manufacturers allows undervolting, and you can't even find out if it's an option in the BIOS even if you look at the pdf manuals available online.
be a way to for undervolting by default on both PIII/Celeron Tualatins and PIV Northwoods. The guys over at Overclockersforums have done a lot of experimenting with raising the default Vcore by wrapping the CPU pins with fine wire to short-together various combinations of pins. By doing this they force a higher default Vcore so they don't have problems as they're first booting up. I think
there may also be pin combinations that give a lower Vcore as well. There's some big, stickied threads in the OCforums Intel section about this issue. It's known as "vidpinning" It might be worth a read if you're serious about doing this but can't find a board that will undervolt. If I hadn't got an ST6 I'd be messing with it myself.
Undervolting my PIII-S has been a very satisfying experience. It's allowed me to run a very powerful CPU with very quiet cooling at very low temps. I'd recommend that more people look into this area.