CPUs aren't 5V or 12V, motherboards are that's why googling the CPU won't find much. The CPUs themselves just get their much lower voltages (1.4-1.5V core, 1.25V bus) from the motherboard.

So370 (or indeed Slot 1 ones) motherboards almost all run the CPU off the 5V line (only some rare industrial boards do 12V). Also AGP gets most power from 3.3V. So you need a PSU that can handle relatively high currents on those lines.

As for being better off with old or new PSU, that's subject of a lot of debate. I personally lean more towards good-quality old PSUs if available (~2000-era ATX is plentiful for almost no money where I live), but an efficient new PSU that can handle the 5V requirements is fine too. If you go for an old one, check the caps before use. Either way, be sure to go for a quality PSU, as - old or new - crappy lightweight ones can't deliver what they promise and risk your components.

It is completely motherboard dependent. You'll have to see if the transistors of the CPU voltage regulator connect to 5 or 12V. On one of my PIII boards it is connected to 12V, on others to 5V.

I've got a dual Tualatin 1.4 system running off of a newer Seasonic 80+ PSU. I'll have to double check the model and wattage as I have a few different models I use.

The other thing about newer, well built PSUs is that the voltage regulation is going to be better and they also supply a lot cleaner power (way less ripple) which in theory should make the power circuitry on the motherboard, etc. run a lot cooler since it shouldn't have to work as hard.

I see.

Tiido wrote:

It is completely motherboard dependent. You'll have to see if the transistors of the CPU voltage regulator connect to 5 or 12V. On one of my PIII boards it is connected to 12V, on others to 5V.

This is new to me. My PIII systems are all 440BX-based, and I have never paid attention to the CPU voltage regulator. It seems to me that all 440BX mobo uses 5V, I'm not sure. I only knew that my 440BX systems run fine with retro PSU (which emphasizes on 3.3v and 5v instead of 12v).

Direct observation aside, is the CPU regulator specification something usually mentioned in the manual? Is it possible to know it beforehand by reading the manual, before actually buying the mobo from ebay?

I have only seen one case in socket 370 where the VRM was not on a 5v rail.
That one was a dual CPU. One CPU VRM was on 5v and the other on 12v.
That was not too unusual on dual AMD boards around that time but I didn't expect it on a socket 370.

Intel recommended switching the VRM's to 12v during the run of socket 370.
IIRC it was in the i810 Platform Design Guide. Many have been the i815.
But then almost no one (including Intel) actually did it until the P4 was introduced.

I agree with the above. Use and old style 5v heavy PSU.
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Kreshna Aryaguna Nurzaman wrote:

is the CPU regulator specification something usually mentioned in the manual? Is it possible to know it beforehand by reading the manual, before actually buying the mobo from ebay?

Not usually mentioned, but Tualatin boards are an exception.
Intel made a big deal about the updated VRM specs being a requirement for Tualatin and that was reflected in advertising and manuals.
Also if you are looking at i815 you need a B-Step version of the chipset.
.
Should help, http://ixbtlabs.com/articles/inteld815epfv/index.html

I think the motherboard manual should generally state what version ATX power supply is "needed".

If anything below ATX 12v 1.3 is specified, then it is going to be more 3.3v and 5v dependent.
The really confusing thing is that v1.3 supposedly was released AFTER 2.0.
https://en.wikipedia.org/wiki/ATX

Anybody have a v1.3 PSU to double check whether or not it is 12v heavy or 3.3/5v heavy?

In any case, the 80+ specification did not exist before 2004.. and most power supplies really were absolute crap in terms of efficiency before then.. even higher quality ones.
https://en.wikipedia.org/wiki/80_Plus

Efficient power supplies are one of my pet-peevs and I follow reviews of them closely. [H]ardOCP is the place to find great PSU reviews since JohnnyGURU doesn't do them anymore.

cyclone3d wrote:

I think the motherboard manual should generally state what version ATX power supply is "needed". […]
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I think the motherboard manual should generally state what version ATX power supply is "needed".

If anything below ATX 12v 1.3 is specified, then it is going to be more 3.3v and 5v dependent.
The really confusing thing is that v1.3 supposedly was released AFTER 2.0.
https://en.wikipedia.org/wiki/ATX

Anybody have a v1.3 PSU to double check whether or not it is 12v heavy or 3.3/5v heavy?

In any case, the 80+ specification did not exist before 2004.. and most power supplies really were absolute crap in terms of efficiency before then.. even higher quality ones.
https://en.wikipedia.org/wiki/80_Plus

Efficient power supplies are one of my pet-peevs and I follow reviews of them closely. [H]ardOCP is the place to find great PSU reviews since JohnnyGURU doesn't do them anymore.

In theory v1.3 was last of the 5v heavy. I think it was the last one to actually require it.
In practice some of the earlier v2.x were pretty heavy on 5v.
I just looked at a v2.0 with 32a-3.3v 32a-5v 18a-12v(x 2 rails)
.
HardwareSecrets had good reviews too. (Not sure if they still do that but the old ones are still around.)

PCBONEZ wrote:

In theory v1.3 was last of the 5v heavy. I think it was the last one to actually require it. In practice some of the earlier v2. […]
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In theory v1.3 was last of the 5v heavy. I think it was the last one to actually require it.
In practice some of the earlier v2.x were pretty heavy on 5v.
I just looked at a v2.0 with 32a-3.3v 32a-5v 18a-12v(x 2 rails)
.
HardwareSecrets had good reviews too. (Not sure if they still do that but the old ones are still around.)

Yeah, my Antec TPII-480 is v2.01 and has 38A-5V, 30A-3.3V and 2x18A 12V rails. I bought it around 2004-2005, there were still plenty of 5V hungry Athlon XPs at the time.

Interestingly, this PSU specifies the max. combined loads for 12V1+12V2 and 12V1+12V2+5V+3.3V, it doesn't say anything about the max. for 5V+3.3V unlike most of the units from that era. I guess it's because of how the different voltages are generated?

TheMobRules wrote:

PCBONEZ wrote:

In theory v1.3 was last of the 5v heavy. I think it was the last one to actually require it. In practice some of the earlier v2. […]
Show full quote

In theory v1.3 was last of the 5v heavy. I think it was the last one to actually require it.
In practice some of the earlier v2.x were pretty heavy on 5v.
I just looked at a v2.0 with 32a-3.3v 32a-5v 18a-12v(x 2 rails)
.
HardwareSecrets had good reviews too. (Not sure if they still do that but the old ones are still around.)

Yeah, my Antec TPII-480 is v2.01 and has 38A-5V, 30A-3.3V and 2x18A 12V rails. I bought it around 2004-2005, there were still plenty of 5V hungry Athlon XPs at the time.

Interestingly, this PSU specifies the max. combined loads for 12V1+12V2 and 12V1+12V2+5V+3.3V, it doesn't say anything about the max. for 5V+3.3V unlike most of the units from that era. I guess it's because of how the different voltages are generated?

Close. - It's how they are regulated. Maybe a little of both depending on the specific PSU.
There are stages after the switching transistors that have parts that supply more than one rail.
Usually it's transformer windings.
The combined ratings are based on the limitations of the shared parts.
The individual rail ratings are based on the limitations after the rails branch off.
.
A loose analogy would be a power strip.
The main plug (to the wall) is good for 15a.
Each individual receptacle is good for 15a.
But the sum of the receptacle's actual loads can't be over 15a - because of the shared main plug.
.