Hello,
The PEX8747 chip is not functioning as it looks, it is nothing more than an attempt to try and make the board seem better than it is.
Your board only has 1x16 slot, this is a direct connection to the CPU.
The PEX8747 is acting as a multiplexing unit.
Real bandwidth CPU 1x16 <PEX> 1x16(a)+1x16(b)
What happens is the PEX controller tries to switch between slots a and b very quickly. (basic description)
E,g
Switch to a for 1ms
Switch to b for 1ms
Repeats cycle to try and pass data back down the x16 link directly to the CPU.
Whatever occurs you must note, x16 is the maximum bandwidth as this is the true CPU link.
So the PEX8747 is not supplying you 2x16, it is a 1x16 time shared (multiplexed) between 2 slots.Now to make matters worse Gigabyte have used another chip between the x16 slots.
A PCI-E Switch, this can split 1x16 to 2x8.
x16 <Switch> 1x8 + 1x8
So forgetting the PEX controller for a moment, this is why on other boards you see that the x16 bandwidth can be shared when populating 2x16 slots. Useful if you don't require the full x16 dedicated to one slot.
On your board there are 2 PCIE switches before the x16 slots, this gives the appearance that there are 4x8 PCIE slots.
Really it is just 1x16.
CPU 1x16 <PEX> [Switch a x16 or 2x8] + [Switch b x16 or 2x8]
Eg if you were to use 4x8
Access switch a for 1ms
Retrieve x8 data slot 1
Retrieve x8 data slot 2
Access switch b for 1ms
Retrieve x8 data slot 3
Retrieve x8 data slot 4
...
Again all passing down a single x16 link.
The PEX8747 is limiting performance.
If you want to test this, try taking out the GFX card, run with the Intel GPU and benchmark the 960 Evo.
If you still get x1 and 900Mb/s the PEX8747 controller is not working correctly with it.
