Depending on the model, a graphics card is fed by either one or two kind of sources:
- the PCI Express slot on the motherboard: this source can provide up to 75 watts to the graphics card.
- the PCI Express power connectors on the graphics card. There are two types of power connectors:
- 6-pin: this power connector can provide up to 75 watts
- 8-pin: this power connector can provide up to 150 watts
For example, the card on the following image (GTX 460) can pull on the PSU a total of: 75 + 2×75 = 225W. Actually the GTX 460 with 768MB of memory has a TDP of 150W. So in theory, one 6-pin power connector is enough. But to handle power demanding applications like FurMark or to have enough place for some nice overclocking, it’s better to have another 6-pin connector.
MSI N460GTX Cyclone two 6-pin power connectors
A GeForce GTX 480 has one 6-pin + one 8-pin: 75 + 75 + 150 = 300 watts for the max possible power consumption. The TDP of the GTX 480 is 250W that’s why there are one 6-pin + one 8-pin instead of two 6-pin connectors.
GeForce GTX 480 power connectors
The N480GTX Lightning is an extreme example: this card has two 8-pin + one 6-pin connectors. So the max theoretical power that the card can pull out of the PSU
is 75 + 75 + 2*150 = 450 watts! Back to Earth, the TDP of MSI’s N480GTX Lightning is actually only 275W.
MSI N480GTX Lightning two 8-pin + one 6-pin power connectors
And the upcoming AMD Radeon HD 6990 with a TDP around 300W will certainly have two 8-pin connectors… And the HD 6970 has a TDP less than 300W: 6-pin + 8-pin (see this news, there are some HD 6970 pictures).