The Gigabyte G1.Sniper M3 comes with two PCI Express 3.0/2.0 x16 slots, one PCI Express 2.0 x16 slot, and one PCI Express 2.0 x1 slot.
The two PCI Express 3.0/2.0 x16 slots are controlled by the CPU, with the first slot working at x16 when only one video card is installed, and with both working at x8 when two video cards are installed. Since these slots are controlled by the CPU, they will offer PCI Express 2.0 bandwidth (8 GB/s at x16) when a “Sandy Bridge” CPU is installed, but PCI Express 3.0 bandwidth (16 GB/s at x16) when an “Ivy Bridge” CPU is used.
It is important to know that, differently from most motherboards, the second PCI Express 3.0/2.0 x16 slot is not the one close to the first slot; it is the third slot of the motherboard, the one closer to the edge of the board.
The third PCI Express x16 slot is controlled by the chipset and always works at x4, offering PCI Express 2.0 bandwidth. This slot is the one in the middle.
So, if you want to install two video cards, the second video card must be installed in the third slot (labeled “PCIEX8”) and not in the second, as is the norm. Also, if you want to install a dual-slot video card in this slot, you will need to use a computer case with at least five expansion slots. (Small computer cases targeted to microATX motherboards usually have four.)
The PCI Express x16 slots support both SLI and CrossFireX technologies.