The ASUS Crosshair V Formula comes with four PCI Express x16 slots, one PCI Express x1 slot, and one standard PCI slot.

The first PCI Express x16 slot (PCIE_X16_1) always runs at x16 speed; the second PCI Express x16 slot (PCIE_X8/X1_2) always runs at x8 speed; the third PCI Express x16 slot (PCIE_X16/X8_3) runs at x16 speed when the second PCI Express x16 slot is empty or at x8 speed when this other slot is used; and the fourth PCI Express x16 slot (PCIE_X4_4) always runs at x4 speed. This way, in order to achieve the best performance if you are installing two video cards, you should install them in the first and third slots, not in the first and second slots as it would appear more logical.

The PCI Express x1 slot is located between the first and the second PCI Express x16 slot, so you will “kill” it when installing a dual-slot video card in the first PCI Express x16 slot. The standard PCI slot is located between the second and the third PCI Express x16 slot, so you will “kill” it when installing a dual-slot video card in the second PCI Express x16 slot. And, since there is no space between the third and the fourth PCI Express x16 slots, you will “kill” the fourth PCI Express x16 slot when installing a dual-slot video card in the third PCI Express x16 slot. In order to install a dual-slot video card in the fourth PCI Express x16 slot, you will need a computer case with at least eight expansion slots (cases usually have seven), and you may block the headers and buttons located at the edge of the motherboard.

All PCI Express x16 slots support both CrossFireX and SLI modes.

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Figure 2: Slots

As you can see in the extreme left-hand side of Figure 2, there is a peripheral power plug to provide more current to the PCI Express x16 slots. The motherboard also has an additional ATX12V connector, located near the memory socket, with the same purpose. You must install these connectors.