MSI Big Bang XPower Review: X58, Military Style
Video Card Power & Configuration
The XPower includes an auxiliary PCIe power connector, but the circumstances in which this ends up being useful are downright esoteric. We contacted MSI for clarification, but the company didn't comment.
Modern video cards draw power from 2-3 rails—motherboard, 12V1, and 12V2. Based on the PCI-Express specification, the motherboard can provide up to 75W of power per individual PCIe x16 slot. The reason, however, that a number of video cards that draw significantly less than 75W still use external power connectors is because the motherboard is only allocated 156W of power at most, assuming two 6.5 amp lines (120W using 5 amp lines).
We didn't include this feature in the overclocking section because it does nothing to improve overclocking performance. The PCIe spec can only provide up to 75W of power per physical slot, no matter how many additional cables are plugged into the motherboard. The entire point of putting a six-pin plug on a lower-end card is to prevent a hungry video card from causing a brownout.
That's a Lot of PCIe x16 Slots...
The real reason MSI added an auxiliary PCIe plug is because the motherboard is capable of running as many as six video cards simultaneously. Even if each card drew just 20W each, they'd suck down 120W in aggregate. We're not sure why anyone would need to run 12-18 displays off a single system, but the additional plug gives the board significantly more power to work with.
If our theory is correct, MSI's port inclusion is a very good thing—but it's not going to boost anyone's overclocking.
One of the most confusing 'features' of modern motherboard design is the total lack of consistency when it comes to which PCI-E slots should be used in multi-GPU configurations. MSI's own diagram is fairly clear:
Dual GPUs are paired in PCIe x16 slots 1&4, triple-head configurations are 1, 4, and 5 (or 1, 3, 5). Quad-cards are 1, 3, 4, and 5, etc, etc.