The ECS P67H2-A comes with three PCI Express x16 slots. The first one always work at x16, and the second one works at x16 when two video cards are installed, but at x8 when three video cards are installed. The third slot always work at x8.
This high-end configuration is achieved by the use of a Lucid LT24102 (a.k.a. “HydraLogix 200”) processor, which is more than a PCI Express switch: it allows you to run multiple video cards in parallel, allowing you to mix and match not only different cards from the same vendor (which is usually not possible with SLI configurations), but allowing you to mix NVIDIA- and AMD-based video cards and make them to run in parallel, similar to what happens on MSI’s Fuzion motherboard series. We were impressed to see ECS, which traditionally manufactures entry-level products, coming with such high-end solution.
You can install dual-slot video cards on all the PCI Express x16 slots, but you “kill” one of the PCI Express x1 slots when a dual-slot video card is installed in the first PCI Express x16 slot. You will need a case with at least eight expansion slots if you want to install a dual-slot video card in the third PCI Express x16 slot (cases usually have seven expansion slots).
The P67H2-A also has two PCI Express x1 slots and two standard PCI slots.