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What is the difference between 20-pins ATX power cables and 24-pins ATX power cables for motherboard? I see that Cooler Master Silent Pro PSU has an extensible plug, showing 20 pins + 4 pluggable pins.

Since I'm having troubles with my motherboard, which has 24 pins, I tried to connect only the first 20 and the system booted up fine.

I'm curious: can any ATX motherboard run with 20-pins power? Will I simply experience lower performance?

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2 Answers 2

up vote 4 down vote accepted

From http://www.playtool.com/pages/psuconnectors/connectors.html#atxmain20 -

You can plug a 20 pin ATX power cable into a motherboard with a 24 pin ATX
connector [...] The 24 pin motherboard connector is actually just the 20 pin
connector with 4 extra pins added on the end. The original 20 pins were
unchanged. The extra 4 pins are not separate rails. They're just extra lines
to provide more current to the same rails. [...] I've never heard of exceptions
and it doesn't make sense for motherboard makers to create any.

and...

A 20 pin power cable only fits into one end of a 24 pin motherboard connector
so you can't insert it incorrectly.

however, it appears that there is no current limiting on a 20 pin ATX PSU, as I assumed there would be...

They added those extra 4 pins for a reason. When you plug a 20 pin cable into a
24 pin connector you're not providing the extra current carrying capacity which
may be needed by the motherboard. If your motherboard's current requirements are
low enough then it will work properly with only a 20 pin power cabled plugged in
. But if the motherboard draws enough current, then you can overheat the 20 pins
you're using on the 24 pin connector. I've seen enough pictures of burned ATX
main connectors to assure you that this happens. [...] Connectors really do get
hot if you overload them so the safest thing to do is use a real 24 pin power
supply on a motherboard with a 24 pin connector. Note that your 24 pin machine
may work fine with a 20 pin power supply until you add a PCI Express card later
on down the road. PCI Express cards can draw up to 75 watts through the
motherboard connector so adding an expansion card can substantially increase
power draw through the main power cable.

Lastly, as an aside:

If you have an ATX power supply with a 24 pin main cable, it's okay to plug it
into a motherboard with a 20 pin connector.

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Possible answer:

http://www.techimo.com/forum/general-tech-discussion/160728-power-supply-use-20-pin-24-pin-board.html

The extra 4 pins are to power a PCI-E graphics card. If you are not using a PCI-E card then it's ok to use the 20 pin connector. If you are using a PCI-E card it's still ok as long as the card has an external power connection and connects directly to the power supply.

Since I've got direct PSU connection on my graphic cards I believe I can run on 20 pins fine, especially if this ceases computer failures

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4  
24 pin added an extra 12v rail to supply more 12v power to the motherboard components that use 12v and take stress off a single 12v wire that the 20pin psu's used, its impossible to say what you are doing is safe or not. Compare the pinout charts on this page, 20pin chart is linked to at the top...pinouts.ru/Power/atx_v2_pinout.shtml –  Moab Sep 6 '12 at 20:29
2  
Generally speaking pci-e graphics cards have their own dedicated power connection and it's not from the motherboard but the psu directly. –  Moab Sep 6 '12 at 20:30
    
@Moab - Have examined both 20 pin and 24 pin ATX connectors and as djechelon answered, the extra pins 11+12+23+24 (From a pin configuration view) are additional +12v & +5v rails. Given this, not sure how this is impossible to say it is un/safe. Further, would be surprised to learn that the organization that specs the ATX connectors, would have made it possible to connect a 20 pin plug to a 24 pin socket, if not safe. –  user66001 Mar 24 '13 at 20:34

protected by Breakthrough Mar 25 '13 at 0:41

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