The MSI Z68A-GD80 (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.
Because of the limited number of PCI Express lanes available, when a video card is installed in the third PCI Express x16 slot, the SATA ports controlled by the Marvell 88SE9128 chip (the eSATA-600 port and the additional SATA-600 port, labeled SATA7), the two USB 3.0 ports available on the front panel header (JUSB4), the FireWire ports, and the two standard PCI slots are disabled. Ouch. This could be solved by adding a PCI Express switch chip, but this addition would increase the cost of the motherboard.
Also, because of the limited number of internal PCI Express lanes, you can’t use both PCI Express x1 slots at the same time.
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 buttons and connectors available at the edge of the motherboard, 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 ASMedia ASM1083 bridge chip.
There is a six-pin auxiliary power connector available to give extra current for the video cards. Unfortunately, the manufacturer doesn’t say exactly when this connector should be used.
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Figure 2: Slots