The ASRock Fatal1ty Z68 Professional Gen3 comes with three PCI Express x16 slots, one PCI Express x1 slot, and two standard PCI slots.
The first two PCI Express x16 slots are connected directly to the CPU integrated PCI Express controller. When only one video card is installed, the first slot works at x16 speed, but when you install two video cards, each slot works at x8 speed. These slots support both SLI and CrossFireX technologies.
This motherboard is touted to have “PCI Express 3.0” (a.k.a. “Gen3”) slots. For a Z68-based motherboard to support PCI Express x16 3.0 slots, two prerequisites are necessary. First, since these slots are controlled by the CPU, you will need to have a CPU with an embedded PCI Express 3.0 controller. Second, the motherboard must use PCI Express 3.0 channel switch chips.
Intel CPUs with an embedded PCI Express 3.0 controller are not available yet. (The first CPU with this feature will be the “Ivy Bridge.”) So, even if you install the latest Intel CPU, the PCI Express x16 slots will still be 2.0, since the PCI Express controller embedded in the CPU is 2.0.
However, this motherboard uses PCI Express 3.0 channel switch chips (NXP L04083B). See Figure 3. This means that when socket LGA1155 “Ivy Bridge” CPUs become available, you will be able to explore the full potential of the PCI Express 3.0 connection – if you have a PCI Express 3.0 video card installed as well. (There are no video cards based on this standard yet.) Motherboards based on the Intel Z68 chipset that use PCI Express 2.0 channel switch chips won’t support PCI Express 3.0, and even if you install an “Ivy Bridge” CPU with a PCI Express 3.0 video card, the slots will work at 2.0 speeds.
The third PCI Express x16 slot always works at x4 speed. Because of the reduced number of PCI Express lanes provided by the chipset, several other motherboards have limitations of what devices can be used at the same time. For example, on some motherboards with three PCI Express x16 slots, the third slot will work at x1 if all additional features such as USB 3.0 ports and the second Gigabit Ethernet port are enabled. To solve this problem, the Fatal1ty Z68 Professional Gen3 has a PLX PEX8608 switch chip, which expands the number of PCI Express lanes available on the motherboard. It works by sensing which devices are not being used and freeing up the PCI Express lane attached to them to other devices.
If you install a dual-slot video card in the first PCI Express x16 slot, you will “kill” one of the standard PCI slots. If you install a dual-slot video card in the second PCI Express x16 slot, you will “kill” the other standard PCI slot; and to install a dual-slot video card in the third PCI Express x16 slot, you will need a case with at least eight expansion slots (cases usually have seven expansion slots), and you may block the headers and connectors located at the motherboard edge.
It is important to understand that Intel chipsets no longer support standard PCI slots, and the PCI slots are provided by an ASMedia ASM1083 bridge chip.