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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?

2 Answers 2

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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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    "not separate rails" this is not guaranteed today. There are many motherboards that are not backward compatible with 20 pin psu. Only old mobos <= 2010 will be 100% backward compatible. Mobo vendor can use these 4 pins to power up pcie clock generator and related stuff, so without these pins pcie may not work.
    – puchu
    Nov 25, 2019 at 11:58
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Possible answer:

https://web.archive.org/web/20151011085026/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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    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, 2012 at 20:29
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    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, 2012 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, 2013 at 20:34
  • techimo link is dead Nov 19, 2018 at 11:27

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