Confused About What PCIe2 Slots Are Compatible

I own Asrock 990 FX Extreme 3 and I'm sure I put graphic card in X16 slot,it's in PCIE2 slot But why is it running in X4 mode,and how to

PCIe2 Slot Characteristics There are five PCIe2 slots available for optional PCIe2 cards The following figure shows the PCIe2 slot numbering

bounty slot Placed in a single PCIe slot Supports the single lane PCIe bus interface Provides 512 MB DDR3 graphics memory Supports DVI or VGA

slotxo pg slot pg deposit 10 get 100 The adapter supports dual port operation in any PCIe3 or PCIe2 slot The adapter supports auto-negotiation, full-duplex only The adapter