ASUS P6T Deluxe has three PCI Express 2.0 x16 slots, one x4 slot and two regular PCI slots. The third x16 slot can’t run at x16 speed, of course (as Intel X58 chipset only offers support for two x16 lanes), so it runs at x1 when the two main x16 slots run at x16. But you can choose to run the third slot at x8, if you lower the speed from the second slot also to x8. In this case the first slot will continue at x16. To use the industry’s language, you have two possible configurations: x16/x16/x1 or x16/x8/x8. If you have only one or two video cards, they will run at x16, of course.
Notice that this motherboard doesn’t have any x1 PCI Express slot. If you have an x1 board you can install it on the x4 slot (or on the third PCI Express x16 slot, if it is available). The x4 slot can’t be used for installing a fourth video card (on Intel DX58SO you can install an x16 video card on the x4 slot available) because the north bridge heatsink physically prevents you from doing this installation.
Motherboards with more than one x16 PCI Express slot based on Intel chipsets have always supported CrossFire configuration, but never supported NVIDIA’s SLI, being the major drawback in having an Intel-based motherboard with more than one x16 slot. The only exception is Intel’s very high-end DX5400XS “Skulltrail” motherboard, which has a couple of small NVIDIA bridge chips to make this happen. This board, however, isn’t targeted to regular users, as it has two LGA771 sockets and supports only FB-DIMM memories.
ASUS P6T Deluxe, however, supports SLI. According to ASUS, SLI support with Intel X58 chipset is possible if the motherboard manufacturer pays a royalty fee to NVIDIA plus passes NVIDIA certification process, which is the case with the present motherboard. So you will see on the market motherboards based on Intel X58 with and without SLI support – to the best of our knowledge Intel’s “Smackover” does not support it, for example. Support will depend on whether the manufacturer paid licensing to NVIDIA and passed their certification process or not – which, by the way, increases the motherboard manufacturing cost and will surely reflect on the product’s price.
SLI support is enabled at driver level, so no bridge chip from NVIDIA was required on the motherboard.
Notice that even though this motherboard has three x16 slots, SLI is limited to two video cards on this board (i.e., no support to three-way SLI).
Interesting enough this motherboard does not require extra power for the PCI Express slots, contrary to what happens with Intel DX58SO. The CPU is fed through an EPS12V connector but half of it comes covered, meaning that you can install an ATX12V connector if your power supply does not feature an EPS12V output.