The Gigabyte Z68X-UD5-B3 comes with three PCI Express x16 slots, two PCI Express x1 slots, and two standard PCI slots.
The first two PCI Express x16 slots are connected directly to the CPU integrated PCI Express controller. Therefore, they work at x16 when only one video card is installed or at x8 when two video cards are installed. They support both SLI and CrossFireX modes. The third x16 slot is connected to the Z68 chipset and works at x4 speed.
If you install a dual-slot video card in the first PCI Express x16 slot, you will “kill” one of the PCI Express x1 slots, and if you install a dual-slot video card in the second PCI Express x16 slot, you will “kill” one of the standard PCI slots. The third PCI Express x16 slot officially supports only single-slot video cards, but you can install a dual-slot card if you have a case with eight expansion slots. However, the video card may block the USB 3.0 front panel connectors and FireWire header, depending on the position and shape of its cooler.
It is important to understand that Intel chipsets no longer support standard PCI slots, and the PCI slots are provided by an ITE8892 bridge chip.