Why special power socket on graphics cards ?

[proon]

What's the point of those six and eight pin power sockets on graphics cards ? If I can get a molex to PCI adaptor, why not just do it onboard and have a four pin molex socket instead ?

 

[Andrew Murdoch]

Molex are designed to have several things running off them. A pci-ex power cable is designed to power a single intensive device, like a cpu power cable or a 24pin mobo connector does.

 

[kanewolf]

The 6 and especially the 8 pin plugs are designed to provide more power than MOLEX. It requires multiple MOLEX usually to provide 8 pin power.

 

[Wisecracker]

Some motherboards used to have molex connectors on-board beside graphic slots -- I suspect there might be a few still out there

 

[proon]

But graphics cards usually come with an adaptor for molex, would they supply this if molex didn't supply the right power ? Would a graphics card steal the power from other components if you put it on the same molex cable ?

 

[Wisecracker]

It's more a question of power delivery.

Older PSUs with molex connectors simply do (or did) not have the juice in some instances -- then OEMs decided to provide 'multiple' 12v power rails.

This kind of worked -- until video cards became more powerful and a single 12v rail with 14-15A just wouldn't cut it in power delivery for cards blowing past 200w. OEMs then engineered 'single-rail' power supplies with 30+ Amps on the 12v rail.

Mobo manufacturers (and the PCIe spec folks) also stepped up and increased voltage available from the slot itself.

 

[giantbucket]

because 4/0 welding cable is just too cumbersome.

 

[Gee Bee]

yes, depending on psu you would ideally have the correct gpu connections. eg I have 4 x 8 pin with the capacity for more beyond my 290x's cf on 6 separate 12v rails. In days long gone a psu could run gpu through molex easily, but that was over a long time ago when high end discrete graphics was nothing like the power requirements we've had for some time now. eg my two cards 840w loaded.

 

[chenw]

But graphics cards usually come with an adaptor for molex, would they supply this if molex didn't supply the right power ? Would a graphics card steal the power from other components if you put it on the same molex cable ?

That's for older PSU's that may have extra molex pins but not sufficient number of PCI-E cables.

a single Molex probably wouldn't be enough to supply a PCI-E socket on its own, GPU includes that adapter so that you can combine two seperate Molex lanes into one that can supply enough current to a PCI-E socket.

 

[proon]

So, what would be the most adaptors you should sensibly use ? I notice that even r9 290x comes with adaptor cables so manufacturers seem to allow ofr some molex usage.

 

[Andrew Murdoch]

So, what would be the most adaptors you should sensibly use ? I notice that even r9 290x comes with adaptor cables so manufacturers seem to allow ofr some molex usage.

That completely depends on how good your PSU is. If it is high quality you should be ok to use a molex>Pci-ex adpater but I would not risk stressing something like the power supply unnecessarily.

You spend a chunk of money on a CPU and GPU, the most cost intensive parts, they should be powered safely by a PSU that meets the new ATX standards.