it says,
the board has this:
4 x PCIe2.0 x16 slots (single @x16, dual @x8, triple @x8, x16, x16 )
PCIE1, PCIE2 and PCIE4 are x16
putting a single card in these will run at x16
two cards (PCIE1 & PCIE2 only) will run at x16 & x8 (2.1a standards)
3-way SLI (1, 2 & 4) ... one would run at x8
this is because they share bandwidth