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A short Power Phase Design explanation

post #1 of 6
Thread Starter 
Phases are structures on your motherboard that supply the overall power to your CPU through VRM's and MOSFET's. They are important with supplying your CPU with power, and if one were to die, the entire motherboard would most likely.

There has been a lot of discussion and debating over which power phase designs are the best and which motherboard to buy for overclocking a specific CPU. Here are the most common power phase designs for motherboards in the market today:

4+1
4+2
4+4
8+2


In these cases, for an 8+2 power phase design for example, 8 phases will be dedicated to the CPU, 1 phase to the RAM, and 1 phase to the HT. Reference.

In some rare cases, you may see motherboards with an upwards of 16 phases, although realistically only necessary with the Core i7 platforms. 4+1 power phase designs are usually found on older, more business orientated motherboards such as the Asus M3A series. In most cases, 4+1 phase designs do not have MOSFET or VRM cooling, therefore it is not recommended you overclock with these boards.

Several boards utilizing the AMD 790X/FX series chipsets most commonly use the 4+2 power phase design. This means that 4 phases will be dedicated to the CPU, 1 to the RAM, and 1 to the HT. Reference and HyperTransport. This is the ideal amount of phase for overclocking. Even the highest quality boards that contain the 790FX chipset uses this phase design. Boards such as the MSI 790FX-GD70.

Then there is the 8+2 power phase design. This is commenly found in the AMD 890GX/FX chipset series motherboards. There are 8 phases going to the CPU, 1 to the RAM, and 1 to the HT. Reference and HyperTransports. These are generally the best boards to do extreme overclocking with as it provides the CPU with 8 phases, therefore giving the CPU more stable power and safer and even better results when overclocking. You will most likely find any 890GX/FX board with this power phase design. The Asus Crosshair IV is an example of one of these boards.

Lastly, there is the 4+4 power phase design. Some may state that this type of powr phase design doesn't exist, but it does in fact exist in "8 power phase design" labels with motherboards. Although it's true that it utilizes 8 power phases, not all 8 are dedicated to the CPU. In fact, only 4 are dedicated to the CPU, 2 to the RAM, 1 to the HT. Reference and HyperTransports, and 1 to the graphics card. However, these extra phases to things like the RAM and graphics card aren't necessary, because most graphic cards have their own phases and power connections and the RAM doesn't usually require more than 1 phase of power. Many tend to be decepted by the "8-power phase design" label and it is always good to do research into a specific motherboard before purchasing it.

So what exactly does having more CPU phases benefit over less? Well, let's use an anology. You have a 4-lane highway with 200 cars passing through it. That's going to be quite a bit of traffic isn't it? The small highway is more susceptable to cause a crash accident. Now take the same 200 cars and pass them through an 8-lane highway. There's more room for cars to pass through and as a direct result, less prone to an accident.

This anology operates in a similar way CPU phases work. 8 phases will provide the CPU with more stable electricity going through them as opposed to the 4 phase design.

Now let's start clearing up some myths. First things first, it's very common to hear of horror stories stating that an overclocker's motherboard spontaneously combusted due to the fact that they were overclocking, despite the fact they weren't using high voltage.

This should not be too much of a concern for those of you with 4+2 phase designs with a heatsink on top of the MOSFET's and VRM's. Usually, in most cases, boards utilizing the 4+2 power phase design and up should not experience any problems overclocking if you stay under the recommended votlage of 1.55v.

It the cases where the motherboard does in fact spontaneously combusts, it most likely is caused by the lack of quality control from the motherboard manufacturer. Perhaps the heatsinks did not make proper contact with the VRM's and caused them to go up in smoke.

But do not be paranoid about purchasing an older motherboard for instance and putting an X6 into it and overclocking it. Just verify you have proper cooling and not to take things over the extreme and you should be okay.
Edited by AMDZ - 12/17/10 at 11:05am
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post #2 of 6
Good write-up. Salient detail though the MOSFETs are part of the VRM, not a separate component. The VRM consisting of a MOSFET and choke and a logic chip.

Lots of info on VRM theory and circuit design for those interested:
http://www.geeks3d.com/20100504/tutorial-graphics-cards-voltage-regulator-modules-vrm-explained/2/
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post #3 of 6
I would not say that you shouldn't OC at all on a 4+1 design board. Only that you should be careful and probably don't go over say 12 to 15 percent. I also would not go past the point where extra VCore is needed. In my case I run about a 12% OC on stock voltage. System is fully stable and the VRMs are not getting hot. Maybe I could push further but I know the limitations of this board so what is the point. Know your hardware and don't push it past what it can take. Some will learn this lesson the hard way however.
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post #4 of 6
Quote:
Originally Posted by AMDZ;11682039 
So what exactly does having more CPU phases benefit over less? Well, let's use an anology. You have a 4-lane highway with 200 cars passing through it. That's going to be quite a bit of traffic isn't it? The small highway is more susceptable to cause a crash accident. Now take the same 200 cars and pass them through an 8-lane highway. There's more room for cars to pass through and as a direct result, less prone to an accident.

This anology operates in a similar way CPU phases work. 8 phases will provide the CPU with more stable electricity going through them as opposed to the 4 phase design.

.... do you have some reference as proof of this?
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post #5 of 6
Thank you! Found this thread from a google search when deciding on which motherboard to get. It might be slightly old but definitely helps!
Edited by -Allen- - 5/29/11 at 11:48am
    
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post #6 of 6
it should be noted that this article is slightly inaccruate in some respects (i.e. there is no 4+4 phase power); I have PMed AMDZ about this before but he has not responded so far. You can view my article in sig for an accurate-as-possible explanation; i believe someone else on Intel forums made an even more accurate article about VRMs.
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