Athlon use +12v instead of +5v ???

Just reading from firingsquad.com Guide about "how to choose a PSU", and the article states that modern processor like Athlon and PIV gets power from the +12v rail.
This is a surprising fact for me, because I always thought Athlon (TBird, Palamino, Tbred) always use mainly +5v. Only PIV use +12v. The article also suggests that high rating for +5v is actually not very useful for current processors like Athlon & PIV. It is the +12v that is most important.

If this is true, then I'm amazed how all articles, postings, recommendations from so many hardware sites & forums seem to focus PSU discussion & power consumption only in the subject of +3.3v & +5v, and their combined power. Very rarely anyone , or any of these articles mentions how important the +12v rail is for processor stability, even for Athlon. No one seems to care very much about the +12v spec in a PSU. This is certainly misleading, because +12v is apparently the most important rail in a PSU that determines the whole stability.

If the article is also true, then the +3.3v & +5v are basically not very important at all, becuase most PSU should have adequately power on these rails just to power up mobos, AGP, and several PCI cards.

Any one to comment and explain ?

Not true. Athlons are indeed very heavy on the 5V line, not the 12V.

*EDIT, looks like some new Athon XP mobo's might be using the +12V, oh my.

Read this.

http://firingsquad.gamers.com/guides/power_supply/

I don't know whether Firingsquad got screwed up the article or what, but it is exactly what they say. It seems the writer have made the research on the subject , even from Athlon processor datasheet.

On Page 2, it says :
Athlon and Pentium 4 CPUs run entirely on the +12V rail and you can determine their power consumption using the following formula that takes into account voltage regular inefficiencies:

There is even a table of the Athlon series power consumption on +12v rail

Serville said:

Read this.

http://firingsquad.gamers.com/guides/power_supply/

I don't know whether Firingsquad got screwed up the article or what, but it is exactly what they say. It seems the writer have made the research on the subject , even from Athlon processor datasheet.

On Page 2, it says :
Athlon and Pentium 4 CPUs run entirely on the +12V rail and you can determine their power consumption using the following formula that takes into account voltage regular inefficiencies:

There is even a table of the Athlon series power consumption on +12v rail

Click to expand...

No. He is wrong in saying that. Why else would PSU's keep bulking up their 5V+3.3V output? For the CPU. Fans and drives use 12.

Here is some good basic info on the subject: http://www.pcguide.com/ref/power/sup/output_Power.htm

Also, the stickies at the top of the Cases and Power Supplies topic address what makes a quality power supply, as well.

agreed. poorly researched article....discouraging..

He actually went through a lot of detail in that article, and did have some good points, but he totally missed the bus on the 12V issue.

Are you guys sure they aren't run off the 12 volt rail? On my motherboard there's a 4pin socket for the power supply to plug into. It says it's 12v for the CPU to make it more stable. It will run without the PSU plugged into it though. This is a MSI kt7 Turbo 2 board for the ATHLON chips. I'd like to know what the bottom line is on this as I've read both ways alot of times. The guy who wrote the firingsquad article isn't the only time I've seen someone say the Amd chips are run off the 12v rail.

Didn't THG's PSU article also say CPUs ran on the 12v line? Until, recently, I thought CPUs were dependent on the 5v line and fans and drive motors dependent on the 12v line.

~THT

I did mail the Author, and this was his response. He indicates that the Nforce2 AMD mobos are putting the cpu on the 12V. That is strange since AMD people usually depend on the 5V. Nevertheless, most AMD cpu's today do indeed need a healthy 5V rail...
Hi Eric,

We are in the process of updating the site to detail that many Athlon boards
derive the CPU core from the +5V -- it is in fact, already mentioned in our
news comments. That said, modern motherboards being produced today,
including AMD boards such as the nForce2 are placing the CPU on the 12V
core. Although it is less efficient and more costly to design the
motherboard in this fashion, moving the CPU to the 12V rail can provide
additional stability, especially under heavy load. The Pentium4 (ATX12V)
runs the CPU on the 12V rail.

Choosing a power supply is a complex task, however, in our experience, the
limiting factor has been the +12V rail. The true measure of the power
supply is difficult since one must determine the power budget from one's
system -- as I mentioned earlier, motherboards vary on whether they draw
from +5V or +12V (both AMD and Intel specs call for +12V), and system
peripherals also vary. In addition, many power supplies with excellent
+3/5V combined power are insufficient for a similar system whose motherboard
relies on the +12V rail. Add the fact that power output can vary by
operating temperature, and that power supply ratings can be questionable,
and it becomes a more complex question. At FiringSquad, we believe that if
you chose your power supply based upon the +12V rail, you will end up
choosing a power supply capable of supporting your system, regardless of the
motherboard. That is, power supplies that can handle large CPU current on
the +12V rail almost certainly have adequate +3/5V power.

Thanks for your input though, and yes, we are in the process of updating the
article for readers who are interested in the additional details.

Sincerely,
Alan Dang

Guys, while it would be nice to know simply for the additional insight it allows, power supply selection does not change as a result. Single voltage current ratings and the nominal total wattage ratings are easily inflated due to the fact that there are no reasonable standards by which these numbers are generated. Manufacturers do (especially makers of low priced units) inflate these numbers in an attempt to win sales. While the 12V consumption is heaviest, exactly how much the supply can make in the absence of any other load is of limited value. And the total ratings are basically only good for identifying the unit in question.

The 3.3+5V spec is far from the end all be all of power supply performance. But it is the only meaningfull spec we are given. As you use a large number of supplies in differing situations you learn that 9 times out of 10 the 3.3+5V value does indeed correlate to the actual load bearing capacity of the supply. This is a lot better than trying to judge based on any single line's output or the nominal total rating.

This all being said, it would surprise me if AMD motherboards aren't moving to a 12V feed for the CPU. Intel did this for a good reason. As CPU current consumption continues to spiral upward it only makes sense to take advantage of the higher power per unit current delivered to the input stage of our CPU's power supply via the 12V line as compared to using lesser voltages. Just like you use 220V to drive heavy loads in the home, a 12V input stage gives us a great deal more efficiency in the face of the ever-increasing electrical load of the CPU.

Well I do know that what I have now depends on the 5V. The PSU's that we buy are geared toward that. My current 400 Watt Antec, for example, does 28A on the +3.3, 40A on the +5, combined 245 Watts. The +12V is only 12A... Works fantastic now, but.... I suppose there may be changes coming....?

While 12A is a bit lower than the current generation of supplies, I wouldn't worry too much. The new Antec SL400 ups this to 18A. Both the FSP/Sparkle 350 and 400W models are rated at 15A on the 12V line. They are extremely stout in practice. While the 12V draw is no doubt rising I don't think your supply will be inadequate anytime soon, but should it be, the cure isn't that expensive.

I am completely surprised to find this fact. The reason is because I just bought a new HEC 400w PSU to anticipate my Epox RDA+ board based on Nforce2 chipset. The board will be available for me in 2-3 weeks. HEC 400w LD-T have the following specs:
+3.3v - 35A
+ 5 v - 36A
+12v - 15A

My choice fell on HEC 400w LD-T simply because I thought the rails for +3.3v & +5v look very good, and the +12v seems ok to power 4 harddrives, 1 CDRW, 1 CDROM, 1 Floppy Drive, and 7 fans (each about 0.3A-0.55A). I know the HEC might still be adequate run all of them, but I anticipate a processor upgrade in the future with perhaps Barton processors 3000+.
If only I know this fact beforehand, I would have looked for a PSU that gives me more juice on the +12v. I guess I was fooled now seeing the fact that even Athlon is moving to +12v.

I see that the PSU choice has now becoming more like a booby trap for anyone who doesn't know the complete technical details of the system he buys. There are still many 300w PSU out there, even a good brand, that supply only 12A for +12v, and this might cause many troubles and frustrations to users, who thought it was enough to drive his system. Lack of standard....that is.

Last week, when I saw some Enermax PSUs, I was still wondering why they give so much juice to the +12v compared to other PSUs. But my choice still fell on HEC 400w because the rating for +3.3v & +5v are better. I guess I was fooled. It seems Enermax has done the right thing.....being more pro-active to anticipate the power needs of many different system.

I really think this whole complication is stupid. The choice of computer components has becoming too confusing for many users.

Serville said:

I really think this whole complication is stupid. The choice of computer components has becoming too confusing for many users.

Click to expand...

Two points, firstly I think your HEC will do fine.

Secondly, if you think choosing computer components now is complex, it would have killed you outright ten years ago. Things are marvelously simple now in comparison. The only simplicity in the old days arose from the fact that you were generally forced into one component, the only one you could afford. People would go on and on why they didn't want this component, or that one, based on this detail or that. But in the end they always bought what was cheapest, just making up whatever story was required to make this sound like the logical decision rather than a desire to spend as little money as possible. But so many refinements to the PC platform have occured, and standardization is at a much higher level now than in the past. And as there is tremendous competition these days, you can actually pick products on their merit rather than taking the only cost effective alternative. The downside is you better be prepared to choose.

At one time people paid for the expertise of professionals. I used to make a very good living building PC's. But nowdays people expect every product to choose itself, install itself, operate itself, and cost nothing. This leaves no room in the equation for professional guidance. People pay vast amounts of money for labor in other industries, but are completely unwilling to do the same with PC professionals. They are the ones that force PC's as whole, and the components, to have the support of a toaster. You get what you pay for. If you are unwilling to pay a mechanic to change the transmission in your car, you best have some knowledge, experience, and tools to do the job yourself. PC's are no different.

well, at 12v fewer amps are needed to equal the same ammount of 'power'. Watts=volts*amps. So the wattage output @ 12v*15a=180w. @ 5v*36a=180w. The 12v doesnt need to be as high amperage, because it makes up for it in voltage.