How to add more than two graphics cards?

[CoinGeneral]

I'm a little bit confused on how to add more graphics cards to the motherboard and this is what I currently have:

http://www.ebay.com/itm/ASRock-970-Extreme3-R2-0-AM3-AMD-970-SATA-6Gb-s-USB-3-0-ATX-AMD-Motherboard-/380760363873?pt=Motherboards&hash=item58a7161361

So as you can see there are only 2 slots for PCI-e and that is enough for only two 7950's... Why then are there some people with four of them on their Asrock 970 extreme3 mobo?

https://bitcointalk.org/index.php?topic=89945.0

I searched on Google and the forums but wasn't able to come up with a straightforward answer, I know it has something to do with riser cables but the slots are 2x PCI-e, 2x PCI, and 2x PCI-x1. Is it in theory possible to have a total of 6 graphics cards on this one mobo using something like the following:

http://www.ebay.com/itm/16X-To-16X-PCI-E-Extender-Powered-Riser-Cable-Adapter-Cord-PCI-E-Express-/161083033002?pt=LH_DefaultDomain_0&hash=item25814c05aa

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[Noruka]

some people use x1 to x16 riser cables and put a card in that slot. for mining theres a negligible difference from what i understand. They utilize all their PCI slots VIA the risers. Alot of people will just get the asrock extreme 4 which has extra x16 slots.

you can in theory use riser cables to plug in 6 but you have to take into account energy requirements, heat generation (biggest factor) and linux is preferred with more than 4 cards.

i find 3 per board is more than enough heat for me to manage

[pontiacg5]

GPU mining doesn't need anything more than a 1x PCI-e link. There are exceptions, but you can generally run a card in every pci-e slot.

The most important thing to watch for is powered risers. The PCI-e bus on the motherbaord is not designed to run so many high powered cards, so it will use too much 12V from the 24 pin connector and burn it up. If you use powered riser cables properly that will never happen.

The second, boards that turn features off when others are in use. Some boards will turn a pci-e slot off if you use the next closest one. Intel SB CPUs don't have as many pci-e lanes, so ivy bridge CPUs are preferred. AMD, I don't know much about. Seems cheaper to set up a intel 6 card board/cpu than an AMD equivalent.

[CoinGeneral]

Aha... It's so obvious now. Thanks.