GPU power: why 2x 6-pins instead of 1x 8-pins

XTF

Gawd
Joined
Oct 11, 2011
Messages
591
Why do (most) GPUs require 2x 6-pins and not 1x 8-pins? A cable and one connector seems a lot cleaner and some PSUs do have one 1x 6/8-pins but not 2x 6. Both should be able to deliver 150W.
 

spine

2[H]4U
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Feb 4, 2003
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2,659
More people have PSUs with only 6 pin adapters compred to those who own PSUs with 8 pin leads.

lowest common denominator.
 

lsun22

Gawd
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Nov 19, 2000
Messages
939
you're right, according to wikipedia

ATX12V v2.1
This is a minor revision from March 2005. The power was slightly increased on all rails. Efficiency requirements changed. Added 6-pin connector for PCIe graphics cards that aids the PCIe slot in the motherboard, delivering 75 watts.

ATX12V v2.2
Another minor revision. Added 8-pin connector for PCIe graphics cards that delivers another 150 watts.

I would say 2x6pin b/c it allows more backwards compatibility. ie it's safer to do a 2x molex -> 6pin. usually the 2x6pins are on seperate rails?. the 1x 8pin, if you needed an adapter.. you'd need what 4x molex -> 1x8pin?
 

alex_wu

n00b
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Jul 3, 2012
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Another benefit I can think of is to distribute power load across multiple 12V rails in a PSU.
Also, on the GPU board design, reduce board power per area distribution.
 

Derangel

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you're right, according to wikipedia

ATX12V v2.1
This is a minor revision from March 2005. The power was slightly increased on all rails. Efficiency requirements changed. Added 6-pin connector for PCIe graphics cards that aids the PCIe slot in the motherboard, delivering 75 watts.

ATX12V v2.2
Another minor revision. Added 8-pin connector for PCIe graphics cards that delivers another 150 watts.

I would say 2x6pin b/c it allows more backwards compatibility. ie it's safer to do a 2x molex -> 6pin. usually the 2x6pins are on seperate rails?. the 1x 8pin, if you needed an adapter.. you'd need what 4x molex -> 1x8pin?

It's been known for a couple years now that both can do 150w, at least on a good power supply. These requirements are done on the assumption that people don't have super high end PSUs with great regulation and so on. A cheap PSU isn't going to be able to hand 150w off of the 6 pin.
 

bexamous

[H]ard|Gawd
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Dec 12, 2005
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1,670
'Its been known for a couple years....' Like someone discovered this hidden truth or something? :p

It doesn't matter what the 6 pin connector can carry, the spec is it only can provide 75 watts. No one is going to put out a card and assume every 6 pin is going handle 150watts.

Answer to OP question is because the set of PSUs with 8 pin connectors is a subset of PSUs that have 6 pin connectors, or other words no PSUs have 8 pin connectors but not 6 pin. Less of a chance customers have problems by using 2 6 pin than having just 1 8pin.
 

XTF

Gawd
Joined
Oct 11, 2011
Messages
591
Answer to OP question is because the set of PSUs with 8 pin connectors is a subset of PSUs that have 6 pin connectors, or other words no PSUs have 8 pin connectors but not 6 pin. Less of a chance customers have problems by using 2 6 pin than having just 1 8pin.
That's not true. There are PSUs that have just one 6/8-pin so they can't power a GPU that requires 2x 6-pin without adapter.

I think the rationale for the PSU design is that 2x 6 would allow it to be connected to CF/SLI which requires an extra 75W compared to powering a single card.


Another benefit I can think of is to distribute power load across multiple 12V rails in a PSU.
Can't you do that with a single 8-pin connector too? It has multiple 12V pins.
 

needmorecarnitine

Supreme [H]ardness
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4,609
It's been known for a couple years now that both can do 150w, at least on a good power supply.



Really?

Did you test this yourself or going by something you read on the net? Wanna share your results or link to the people who claim this?
 
Joined
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Messages
2,263
Really?

Did you test this yourself or going by something you read on the net? Wanna share your results or link to the people who claim this?

Well it can be solved by simple logic that it depends on the PSU and not the 6-pin-8-pin connector. If the PSU has the power necessary then the 6-pin can output that figure. All you do to fill a 8-pin female with a 6-pin male is to splice a single wire(correct gauge) with two proper pin ends and plug it into the left over two female pins. It's just ground wires and this is a well known work around. :p

It has been known since the 8-pin pci-express standard was created. Creating an 8-pin pci-express connector was just a way to idiot proof against the ignorant overloading their power supplies. Possibly to increase sales of new power supplies at the same time.
 
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needmorecarnitine

Supreme [H]ardness
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Feb 10, 2004
Messages
4,609
Well it can be solved by simple logic that it depends on the PSU and not the 6-pin-8-pin connector. If the PSU has the power necessary then the 6-pin can output that figure. All you do to fill a 8-pin female with a 6-pin male is to splice a single wire(correct gauge) with two proper pin ends and plug it into the left over two female pins. It's just ground wires and this is a well known work around. :p

It has been known since the 8-pin pci-express standard was created. Creating an 8-pin pci-express connector was just a way to idiot proof against the ignorant overloading their power supplies. Possibly to increase sales of new power supplies at the same time.


Wow, you must be like a scientist or something.

:)
 

Trimlock

[H]F Junkie
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Sep 23, 2005
Messages
15,228
There isn't really an answer to this question, is there?

Simplify the board layout and power design of the board. Your highend will have 2x6 pin power connectors, your step down will have the same board but use one 6 pin, this solves the problem of having two different designs for boards.
 
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