PCIe Compatibility Question

[ethraax]

Will a PCIe x8 card (in this case, a RAID controller) work in a PCIe x16 slot that's running in PCIe x4?

I ask because I'm looking to buy a RAID controller, but some of the higher end ones are PCIe x8 cards, and my motherboard (Gigabyte P55A UD3) only has a slot that's physically as big as a PCIe x16 slot, but says it only runs in PCIe x4.

Of course, I only expect the bandwidth from four channels, not eight. To see what I mean, here's the manual: http://download.gigabyte.us/FileList/Manual/mb_manual_ga-p55a-ud3_e.pdf

Will a PCIe x8 card run, but at half speed, or will it not run at all?

 

[bastage]

Will a PCIe x8 card (in this case, a RAID controller) work in a PCIe x16 slot that's running in PCIe x4?

I ask because I'm looking to buy a RAID controller, but some of the higher end ones are PCIe x8 cards, and my motherboard (Gigabyte P55A UD3) only has a slot that's physically as big as a PCIe x16 slot, but says it only runs in PCIe x4.

Of course, I only expect the bandwidth from four channels, not eight. To see what I mean, here's the manual: http://download.gigabyte.us/FileList/Manual/mb_manual_ga-p55a-ud3_e.pdf

Will a PCIe x8 card run, but at half speed, or will it not run at all?

Yes it should be fine at PCIe 4x speeds