Gigabyte 990FXA-UD3 Motherboard
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The Gigabyte 990FXA-UD3 comes with four PCI Express 2.0 x16 slots, two PCI Express 2.0 x1 slots, and one PCI slot.
Two of the PCI Express x16 slots (PCIEX16_1 and PCIEX16_2) always work at x16 speed, and the other two slots (PCIEX4_1 and PCIEX4_2) always work at x4. Therefore, when installing two video cards, place them in the first (PCIEX16_1) and third (PCIEX16_2) slots for best performance.
If you plan to install a dual-slot video card in the fourth PCI Express x16 slot (PCIEX4_2), you will have to buy a case with at least eight slots. (Computer cases usually have seven.)
When installing dual-slot video cards, you “kill” the slot immediately to the left of the slot being used (looking at the motherboard with its rear connectors facing up). This means that you can’t install a dual-slot video card in the second (PCIEX4_1) PCI Express x16 slot, because you will block the third (PCIEX16_2) slot, which is faster than the second. Therefore, even though this motherboard has four PCI Express x16 slots, only three of them can be used with dual-slot video cards.
The first and the third PCI Express x16 slots support both SLI and CrossFireX technologies.
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