The ASRock Z77 OC Formula comes with two PCI Express 3.0/2.0 x16 slots, one PCI Express 2.0 x16 slot (working at x4), and two PCI Express 2.0 x1 slots.
The two 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, and with both working 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 x16 slot (PCIE5) is controlled by the chipset, always works at x4 speed, and uses 2.0 bandwidth. You will need a computer case with at least eight expansion slots if you want 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.
The portrayed motherboard has a series of three switches for you to enable or disable the PCI Express x16 slots. These switches are useful when you have more than one video card installed and you want to check which one is faulty without removing all of them from the computer.
In order to properly accommodate the additional PCI Express devices that are on this motherboard (the additional SATA and USB 3.0 ports), the board makes use of a PLX PEX8605 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.