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CPU power pin confusion

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April 14, 2011 5:56:42 AM

Hello everyone,

I've just got a quick question regarding 4-pin and 8-pin CPU power interfaces on current motherboards.

I built my current machine about a year ago with an AMD Phenom II x4 955 BE and an MSI NF980-G65. That MSI board has two 4-pin CPU power interfaces and since the 955 is a 125W CPU, I ( not knowing for sure if what I was doing was accurate ) used both of the 4-pin power interfaces and ( happily! ) everything has been purring right along ever since.

However, when I built this machine, I went from a single core Socket A AMD XP 1800+ to the 955 so I totally skipped the dual-core era and related hardware.

Now to my actual question... >:) 

I'm currently building a new machine for my mom and have chosen the AMD Athlon II X2 260 Regor AM3 3.2GHz 65W Dual Core CPU for her and an MSI 870A-G54 AM3 AMD 870, which, like my board, has two 4-pin CPU power interfaces.

So... because her CPU is only a 65W processor, should I use both of the 4-pin power connectors on the motherboard or just one of them?

In my mind, I think that I should only use one because a 65W CPU is not going to need near the amount of power that connecting both 4-pin power connectors would provide, and might (?) even overload and fry a 65W processor. On the other hand, 125W CPUs like the 955 and the X6 series, etc do indeed need that extra power and do need both of the 4-pin connector to be connected.

Is that correct? Have I answered my own question or am I way off?

Any info you guys have would be greatly appreciated.

Thanks again! :) 

Best solution

a b à CPUs
April 14, 2011 6:07:34 AM
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If the mainboard has two 4-pin plugins and your power supply has two 4-pin plugs, use them both. The CPU won't be overloaded -- it will only draw what it needs. The board may not boot with only one of them plugged in anyway.
a c 172 à CPUs
April 14, 2011 8:37:53 AM

The board will boot with one 4 pin plug installed. But if you have both 8 pin connectors, install them both. You have nothing to lose.
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April 14, 2011 2:09:57 PM

^ +1 - for both of the above two posts..
Reason is that, although not required/needed, By using the 8 pin vs the 4 pin setup you will reduce the IR drop (Voltage loss) between CPU VRMs and the +12 V PSU rail. Although not a significat reduction, any reduction in IR losses is always good.

Added:
This also explains why the 8 pin is required for CPUs with > 125 Watts (also true for 95 Watt CPUs that are overclocked). With 125 Watt and greater CPU the IR drop across the pins on a 4 Pin connection would be excessive and possibly melt the plastic around the socket. With the 8 pin the individual IR drop (4 parallel paths instead of two) is reduced and prevents this overheating.
April 14, 2011 8:56:03 PM

Ok cool. I totally understand now!

Thank you guys for your great info and really speedy responses. I appreciate it greatly :D 
May 7, 2011 3:50:08 AM

Best answer selected by agabougi.
a b à CPUs
May 7, 2011 8:47:52 AM

This topic has been closed by Maziar
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