Gigabyte P55 board with Turbo SATA3/USB3.0 reduces graphics card PCIe bus to 8X when USB3.0 is enabled

From the manual of GA-P55A-UD3P, it is stated that when the Turbo SATA3 or USB 3.0 is enabled, the PCIe graphics slot will drop from PCIe x16 to PCIe x8.

You would have to choose if you want maximum graphics performance or maximum disk performance. These new boards uses the NEC 3.0 chip and SATA 3 which requires more bandwidth than just PCIe x1. As the P55 and CPU does not have enough lanes to support, the PCIe x16 is reduced to PCIe x8.

Although PCIe x8 won’t give you much of a performance dip, it gives you maximum USB3.0 performance at the expense of the 8 lane instead of 16. Now the issue is, if we still want Turbo SATA3 and USB 3.0 and want SLI or CrossFire with 2 cards. Will the two PCIe slots be running at Dual 4x (4x + 4x) ? Do let us know if you own the P55 series of boards with NEC USB 3.0 on board.

Gigabyte has replied to us

First of all, if users really want to use CrossFire / SLI on a P55 motherboards, as you know the PCI-e x16 lanes will split into 2 x8 lanes, besides that users are still able to enjoy the benefits of USB 3.0 and SATA 6G.

It is only when user is using one graphics card, then the user is able to select whether he wants to use the full bandwidth of USB 3.0 or SATA 6G.  Of course, according to our manual had clearly stated the PCI-e graphics will operate in x8 mode. But the true fact is, there’s no identical performance drop comparing with a PCI-e x16 to a PCI-e x8 graphics.

Plus, our implementation gives users a more flexible choice and paying less money to enjoy USB 3.0 / SATA 6G.

When CF/SLI is running in dual 8X, the SATA3 and USB3 will be running in non turbo mode, getting the PCie lane from the P55 chipset instead of from the CPU, thus allowing the CF/SLI to run in Dual 8x mode.