The Intel(R) Desktop Board DP45SG provides support for PCI Express* Revision 1.0a; see page 9 of the Technical Product Specification:
Have you tried with a video card that meets this requirement?
That is for the "Instantly Available PC Technology" which i dont even use or plan to use.
If you go to page 10 of that same manual you will see "Expansion Capabilities"
You will notice the following is listed:
Two PCI Express 2.0 x16 bus add-in card connectors
I am not doing SLI or CROSSFIRE...
I have 1 BFG 9800 GT with 1GB
This card uses a PCI Express 2.0 slot.
The card requires a PCI Express or PCI Express 2.0 - compliant system motherboard with one vacat PCI Express x16 slot.
According to both manuals the x16 width should be active and not showing x8 in the bios and according to the program cpuid inside the os.
Well I did some trial and error along with reading further in the linked PDF.
First off things are a bit misleading, but page 18 item 1.6.1 sums it up nicely. There are 2 PCI Express x16 connectors on the motherboard. Only 1 of these slots is truely configured and capable of doing x16. This is the primary slot. I tested this by actually moving my video card from the primary slot to the secondary and it would only ever link up at x8.
Second off if ANYTHING is in that secondary slot the first automatically runs at x8. This includes my x1 PCIE tuner card that trips the second slot populated and automatically cuts the first slot to x8.
Third it seems if I want 2 PCIE tuner cards I will have to use the PCIE x1 connectors. That first slot would be unusable if I had a fat card, but my card is single slot width. My tuner card luckily only cover half of the fan. Sadly the surface mount caps on the tuner cap but right up against the video card cooler. Sadly I can't accept this tight slot, but I know I have too. I wedge a card stock between the cooler and the tuner. This will create some heat issues later I am sure. I confirm the video card is x16 and both tuners are working at least even if they operate in x1 mode.
Board makers should wake up and understand that people would like to use a card slot if it is on the board. Stop placing card slot right next to the PCIE x16 connectors when over 95% of the newer cards take up 2 slots. The other option is to not be misleading with he 2nd PCIE x16 slot and allow a user to at least use for primary single operation at x16.
Hopefully this aid other users of this motherboard.