The MSI Z77A-GD65 comes with three PCI Express 3.0/2.0 x16 slots and four PCI Express 2.0 x1 slots.

The three PCI Express 3.0/2.0 x16 slots are controlled by the CPU, with the first slot working at x16 when only one video card is installed, with the first two slots working at x8 when two video cards are installed, and with the first slot working at x8 and the other two slots working at x4 when three video cards are installed. Since these slots are controlled by the CPU, they will offer PCI Express 2.0 bandwidth (8 GB/s at x16) when a “Sandy Bridge” CPU is installed, but PCI Express 3.0 bandwidth (16 GB/s at x16) when an “Ivy Bridge” CPU is used.

It is important to understand that on most motherboards with three PCI Express x16 slots based on the Intel Z77 chipset, the third PCI Express x16 slot is 2.0 and controlled by the chipset; as explained, on the MSI Z77A-GD65 the third slot is controlled by the CPU and, therefore, 3.0 when an “Ivy Bridge” CPU is used. However, in order to make this possible, the speed of the second PCI Express x16 slot is reduced to x4 when three video cards are installed.

Currently, there is no visible performance gain in using PCI Express 3.0. Therefore, we believe it would make more sense to leave the third PCI Express x16 slot as 2.0 and controlled by the chipset, so the second PCI Express x16 slot would always work at x8 speed. However, in order to do that, the manufacturer would have to possibly cut the number of PCI Express x1 slots, as the chipset doesn’t have enough PCI Express x1 lanes.

If you want to install a dual-slot video card in the third PCI Express x16 slot, you will need a computer case with at least eight expansion slots. (Computer cases usually have seven.)

The PCI Express x16 slots support both SLI and CrossFireX technologies.

click to enlarge
Figure 2: Slots