Dual Video Cards, Crossfire/SLI

1. Modern graphics cards use PCI express, usually in 16x width, although they are only bottlenecked a tiny bit using 8x width. This is commonly referred to as PCIe16 or something similar.
2. Crossfire is for AMD/ATI graphics cards, SLI is for Nvidia cards. The way it works is that two cards are placed in two PCIe slots on the motherboard (consult motherboard manual for specifics about which slots). A connecting bridge is then placed on a "finger" of each card, which is a small projection on the opposite side that it connects to the motherboard. Just google Sli bridge or crossfire bridge to see a picture.
3. Not all motherboards with multiple PCIe slots support Crossfire or SLI. They may support one or the other or neither, or sometimes both.
4. You can even add three or sometimes four graphics cards together (For nvidia, the max is basically 3, for AMD it is 4). Only cards that have two connecting fingers on them can be used in 3x sli or 3x/4x crossfire. This is because the first and second cards connect with the first fingers on their cards, and the second and third cards with the second fingers on their cards.
5. Nvidia and AMD offer behemoth cards that have two graphics chips on the same cards. These chips function in sli/crossfire, even though they are on the same card. They are quite expensive and use a lot of power, but are extremely powerful and allow those who do not have more than one free PCIe slot open to run sli/crossfire on their machine. Such cards include the Radeon 6990 (which is two radeon 6970s on one board), GTX 590 (which is two GTX 580s on one board), and I think there might be a GTX 460 x2 card by zotac or something but it's not an official product in nvidia's lineup.

Thank you very much, this has been most helpful. I think I'll be able to figure it out with the information you provided. One quick question, though. Are there specific types of connecting bridges for different cards, or would an XFX Crossfire Bridge function with any crossfire enabled card?

Thanks for the quick reply!

Thanks to you both. I really appreciate your helpful and timely responses. I think that's all I needed to know, I just wasn't quite sure how the whole having more than one graphics card thing actually worked. Thanks again!

Best answer selected by camouflage212.

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