PCI Express Selector
Common Options : x16 x1 Mode, x8 x8 Mode, Auto
This is an Intel X58 Express chipset-specific BIOS setting. The Intel X58 Express chipset supports a maximum of 36 PCI Express lanes directly from its I/O hub. While the availability of 36 PCI Express lanes allows for at least two full PCI Express x16 slots, the third slot would be limited to just 4 PCI Express lanes (x4).
To circumvent this limitation, and provide greater flexibility, some motherboard manufacturers equip their X58 Express motherboards with three PCI Express x16 slots. Only the first PCI Express x16 slot will always have all 16 lanes enabled. The link width of the second and third PCI Express x16 slots will be adjusted according to the user's requirements. This feature is controlled by the PCI Express Selector BIOS setting.
When set to x16 x1 Mode, PCI Express slot #2 will utilize all 16 lanes while PCI Express slot #3 will only use a single PCI Express lane.
When set to x8 x8 Mode, both PCI Express slots #2 and #3 will utilize 8 lanes each.
When set to Auto, the BIOS will detect the installed cards and set the mode accordingly.
If you are only using a single PCI Express x16 graphics card and it is installed in the first PCI Express slot (which is always running in x16 mode), you can safely ignore this BIOS setting. If you install it in the second PCI Express slot, you should set it to the x16 x1 Mode to ensure that the second PCI Express slot runs with all 16 lanes enabled.
If you are using two PCI Express x16 graphics cards (in SLI / CrossFire / PhysX mode), you should select the x16 x1 Mode to allow both PCI Express slots to run in the full x16 mode.
If you are using three PCI Express x16 graphics cards (in SLI / CrossFire / PhysX mode), you should select the x8 x8 Mode to provide all three cards with the best spread of PCI Express bandwidth.
If you are not sure what to select, then it's best to leave it at the default setting of Auto.
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