The Intel DX79SI comes with three PCI Express 3.0 x16 slots, two PCI Express 2.0 x1 slots, and one standard PCI slot. Socket LGA2011 processors have a total of 40 PCI Express 3.0 lanes for video cards. This allows a very high-end configuration for the PCI Express x16 slots, but the exact configuration used will depend on the motherboard model.
The first and second PCI Express x16 slots always run at x16 speed, while the third PCI Express slot always works at x8 speed.
When installing dual-slot video cards, you “kill” the slot immediately to the left (looking at the motherboard with its rear connectors facing up) of the slot being used. The installation of three dual-slot video cards can be done using a regular seven-slot case.
All PCI Express x16 slots support both SLI and CrossFireX technologies.