The ASRock Z77 Professional comes with two PCI Express 3.0/2.0 x16 slots, one PCI Express 2.0 x16 slot, two PCI Express 2.0 x1 slots, and two standard PCI slots.
The two PCI Express 3.0/2.0 x16 slots are controlled by the CPU. The first slot works at x16 when only one video card is installed; both work at x8 when two 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.
The third PCI Express 2.0 x16 slot is controlled by the chipset and always works at x4 speed. You will need a case with at least eight expansion slots if you decide to install a dual-slot video card in this slot. (Computer cases usually have seven expansion slots.)
The PCI Express x16 slots support both SLI and CrossFireX technologies.
Since the Z77 chipset doesn’t support standard PCI slots, these slots are connected to PCI Express x1 lanes using an ASMedia ADM1083 bridge chip.
In order to properly accommodate the additional PCI Express devices that are on this motherboard (the third PCI Express x16 slot, the second Gigabit Ethernet port, the four additional USB 3.0 ports, the four additional SATA-600 ports, etc.), the board makes use of a PLX PEX8608 switch chip. This chip automatically switches the available PCI Express lanes to the devices that need them. On motherboards with too many PCI Express devices without a switch chip, you need to manually disable devices on the motherboard setup in order to achieve full performance on devices connected to the USB 3.0 and SATA-600 ports when transferring files at the same time.