The Gigabyte Z87X-UD7 TH comes with five PCI Express 3.0 x16 slots and two PCI Express 2.0 x1 slots.
Usually, on motherboards based on the Z87 chipset, only the first two PCI Express x16 slots are controlled by the CPU. The other PCI Express x16 slots are controlled by the chipset, operating at a lower speed (x4 or x1) and only compatible with 2.0 specifications, which offers half of the 3.0 bandwidth. On this motherboard, however, the four slots are controlled by the processor, using a PLX PEX8747 switch chip, thus all slots are PCI Express 3.0.
The second PCI Express x16 slot (PCIEX16_2) bypasses the switching chip, so it must be used if you are installing only one video card. But if one of the other PCI Express x16 slots is in use, it is disabled.
The third PCI Express x16 slot (PCIEX8_1) shares bandwidth with the first one (PCIEX16_1), which means that the first slot works at x16 speed if the second one is not used, and at x8 if there is a video card installed in the second one. The same happens with the fourth and fifth slots. So, the possible slot configurations are x0/x16/x0/x0/x0, x16/x0/x0/x16/x0, x16/x0/x0/x8/x8, and x8/x0/x8/x8/x8.
All the PCI Express 3.0 x16 slots support both SLI and CrossFireX technologies.
The PLX PEX8747 chip, which allows the high-end slot configuration, is shown in Figure 3, without its heatsink.