how important are the +3.3/+5 rails in a modern computer?

[spazo]

With all the talk about the +12 rail what about the the other rails? Do they need to be highly powered in order to run a modern system?

 

[Hacp]

Nope. Very few things run on the 5rail. I think usb/speakers/etc runon the 5rail but i'm not too sure. I think ram runs on the 3.3 rail but not to sure. Hds/optical drives/floppies/mobo/graphics card/cpu run on the 12rail I think.

 

[JDCentral]

Wait.. I thought that the 12v rail was the unimportant one?

I may be wrong, but I remember people stressing the 5V rail, 'cause that's what the mobo/proc runs on.

The 12V rail is for hard-drives, fans, optical drives, video cards, etc...

COrrect me if I'm wrong, though.

 

[Bona Fide]

Most new ATX motherboards run on a 12V rail, to my knowledge.

 

[Lonyo]

Originally posted by: spazo
With all the talk about the +12 rail what about the the other rails? Do they need to be highly powered in order to run a modern system?

No they don't.
They are still important, obviously, but really you don't need a 40A 5v rail when the 12v rail is 12A or something stupidly low.

 

[suszterpatt]

Originally posted by: JDCentral
Wait.. I thought that the 12v rail was the unimportant one?

I may be wrong, but I remember people stressing the 5V rail, 'cause that's what the mobo/proc runs on.

The 12V rail is for hard-drives, fans, optical drives, video cards, etc...

COrrect me if I'm wrong, though.

You're wrong. 😉



Newer systems run the CPU off the 12V rail. Graphics cards eat more and more power, and higher speed drives are getting more popular.

 

[TSCrv]

i doubt newer mobos use the onboard regulator to use the 12v for the cpu when they have 5v and 3.3v allready there... >.<

 

[hclarkjr]

here are some links that will help you guys out on what rails do what in power supplies -
link 1
link 2
the first link states specificly what each does and the second has a lot more info but other aspects as well, hope this helps 🙂

 

[Mark R]

i doubt newer mobos use the onboard regulator to use the 12v for the cpu when they have 5v and 3.3v allready there

That's exactly what they do.

Let's say your CPU needs 100 W of power. It's a lot easier to move 8.5 A of 12 V power, than it is to move 20 A of 5 V power. Less stress on connectors, thinner traces needed on the motherboard (freeing up space for other components) and better voltage stability.

Some manufacturer's (like Epox) used to use the 5V for CPU up until very recently - the result, sagging voltages and burned-out Molex connectors. Every mobo manufacturer has now abandoned using 5V to power Pentium 4 and Athlon class CPUs.

 

[Zepper]

If the mobo has the P4 connector, it is running the CPU off +12V so you want the total power of the PSU weighted more toward the +12 rail(s). Fancy video cards are also sucking +12 now so if you have one of those too, then weigh even more toward +12. However if you have an old style mobo (w/o the P4 connector) and an old style video card w/o an aux power connector, you want the weighting to go toward the +5 rail.
. Motors on drives run off +12 (fairly high current - ~2A starting, ~1A running for HDs), the rest of the circuitry on the drives runs off +5. Notebook drives run entirely on +5 which is partially why they are so much slower than desktop drives.
. For the same wattage rating PSU, you will be taking more than 12 Amps total off the other two rails to add 5 Amps to the +12 rail(s).

.bh.