The Gigabyte Z77X-UD4H comes with two PCI Express 3.0 x16 slots, one PCI Express 2.0 x16 slot (working at x4), three PCI Express 2.0 x1 slots, and one PCI slot.
The two PCI Express 3.0 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, it 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.
The third PCI Express x16 slot is 2.0 and works at x4. If you plan to install a dual-slot video card in this slot, 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).
Since the Intel Z77 chipset doesn’t support standard PCI slots, the motherboard uses an ITE IT8892E bridge chip to connect the standard PCI slot to a PCI Express x1 lane.
The PCI Express x16 slots support both SLI and CrossFireX technologies.