tohle je od Gigabyte:
Normal Mode: Only the first PCIE x 16 slot is available and can operate at up to x 16 in Normal Mode.
SLI Mode: In SLI Mode, the two PCIE x 16 slots can run in two modes. You can either use them as two
individual x 8 slots or install two SLI-ready PCIE x 16 cards

the table below to check PCIE slots available in SLI or Normal Mode before installation.
SLI Mode
Normal Mode
PCIE_1 PCIE_16_1 PCIE_2 PCIE_16_2
Available Available* Not available Available*
Available Available Available Not available
"*" can run at up to PCIE x 8 mode.
1. Installing a device to a PCIE slot when it's not available might damage the system.
2. We do not recommend removing the SLI switch module from the motherboard because
in that case, all PCIE slots will not be available except for the PCIE_16_1 slot, and the slot
can be used only as a PCIE x 8 slot.