Which power rail does CPU use?

er excuse me but which power rail does the CPU end up using?

what about those auxilary connectors for P4's?

I'm wondering if my PS is sufficient for dual 3.6 GHz 1.3v Xeons under load.

thanks ...

Almost all motherboards use the 12V rail for the cpu. That P4 connector has 2 grounds and 2 12V lines.

There are some weired motherboards around that use the 5V rail, but any newer board with the P4 connector or one that can support a precott or A64 (or high model XP) will deffinatly use the 12V rail.

thanks!

So I'll look at the amps on the +12v rail and see if it can provide >200 watts. I'd want at least 16 amps then ... how much overhead should I allow for? Should it have 25% more amps than it technically needs ... or what?

A lot depends on the rest of your system. The video card is another component that can suck a lot of power from the 12V line, and the hard drives and a few other components take some power too.

What is the powersupply in question? chances are that unless it is a beast you will have to get a new supply.

Well it is a bit of a beast. I am just checking on the work of the local computer store.

I think it is this one - Sparkle FSP460-60PFN-EPS 460W Dual Intel Xeon Power Supply
http://www.xpcgear.com/spfs46duinxe.html

Only says 15A on the 12v rail though ... misprint? It has 2 12v rails, one for each proc?

I modded it for a quieter fan (2/3 the amps on the fan, 0.15 instead of 0.22) and it poops when the duals are under load. Looks like PS shuts itself off after a couple of minutes.

So it's probably my fault but I'm checking. An 0.22A 80mm fan is probably the bare minimum for it, considering how much the PS is obstructed inside. It does thermally adjust the fan so it's probably operating at its heat margin all the time anyhow, and 2/3 the fan power just cuts way too far into the margin.

Ironically, when I thought the PS was loud, it was probably just something else.

Thanks for the help Matt.

PS The video card is pretty generic, Radeon 7000 or whatnot.

PPS I'm tempted to cut up the power supply and thermal-adhesive an old XP heatsink to what appears to be its aluminum heat conductor.

how much cash are you willing to spend on a PSU - i'd suggest one of the PC P&C's for dual xeons, but they're >$200, though keep in mind that a good PSU is the backbone of a solid system


edit: what mobo are you using? i'll get you a link to the specific PSU