So here's the situation:

I have an older GeForce 8600 GTS graphic card in my PC, and I have ordered off ebay an HP P420 raid card which is PCI Express 3.0 x8 (it has not arrived yet).

I had a look at my mainboard before ordering and saw it had 3 PCI Express x16 slots. Figuring I can stick a x8 card into one of the spare x16 slots I went ahead and ordered it.

However, today I was looking at my mainboard manual (Asus Z170-AR) and saw the following describing the expansion slots:

2 x PCI Express 3.0/2.0 x16 slots (single at x16 or dual at x8/x8 mode)

 

1x PCI Express 3.0/2.0 x16 slot* (max. at x4 mode, compatible with PCIe x1 and x4 devices)

 

3 x PCI Express 3.0/2.0 x1 slots

 

1x PCI slot

 

* The PCIe x16_3 slot shares bandwisth with SATA6G_56. The PCIe x16_3 is default set at x2 mode.

My graphics card is in x16_1 slot, and I have nothing in x16_2 or x16_3.

So what happens when I connect the RAID card to the x16_2 slot, will it work? Do I have to lower the operating mode of x16_1 slot to x8 in order to make x16_2 slot work?

EDIT: It looks like my old graphics card in x16_1 slot is PCI Express 1.1, will this slow down the PCI Express 3.0 RAID card going into x16_2 slot?