PCIe 2.0 x 16 and Crossfire

[dmmorgan]

Hi all, I'm just finishing off plans for a new budget-ish gaming build, but had some questions about PCIe 2.0...I'm buying a P55 to run an i5 and one 5770 (for now), but wanted the option to throw in a second in Crossfire in a couple of years as a cheap gfx upgrade. I'm just wondering what the limitations of having only one PCIe 2.0 x16 slot are...what sort of hit would I take having one PCIe 2.0 x16 and one PCIe x16? (or two PCIe x16) compared to two PCIe 2.0 x16? Apologies if anything I've said doesn't make complete sense, I don't have much of an idea what I'm talking about : P. ta!

 

[megamanx00]

Well, with a P55 board the number of PCI-E lanes are on the CPU itself. Such CPUs have 16 PCI-E 2.0 lanes for graphics. Boards that have two 16x length slots divide the available lanes to 8x for each slot unless the board is equipped with something like the NF200 chip.

 

[JackNaylorPE]

Usually I see P55's with one PCI-E x 16 or two PCI-E x 8 which would be bandwidth limiting w/ higher end GFX cards.

 

[warmon6]

Hi all, I'm just finishing off plans for a new budget-ish gaming build, but had some questions about PCIe 2.0...I'm buying a P55 to run an i5 and one 5770 (for now), but wanted the option to throw in a second in Crossfire in a couple of years as a cheap gfx upgrade. I'm just wondering what the limitations of having only one PCIe 2.0 x16 slot are...what sort of hit would I take having one PCIe 2.0 x16 and one PCIe x16? (or two PCIe x16) compared to two PCIe 2.0 x16? Apologies if anything I've said doesn't make complete sense, I don't have much of an idea what I'm talking about : P. ta!

Well let me brake this down.

I'm just wondering what the limitations of having only one PCIe 2.0 x16 slot are

Well, with one 1 pci-e 2.0 x16 you would be limited to able to use 1 graphic card. other than that you'll have no other limitations.

what sort of hit would I take having one PCIe 2.0 x16 and one PCIe x16? (or two PCIe x16) compared to two PCIe 2.0 x16?

Well it unlikely you'll have 2.0 and 1.0 X16 slot. Most manufactures should have put all 1.0 slots or 2.0 slots on there motherboards.

For having two 1.0 x16 you would have the same performance as two x8 2.0. 2.0 (in theory) has twice the data transfer of 1.0.

Although i wouldn't worry to much about all the different PCIe slots, 1.0 and 2.0 at the moment. Even the most powerful graphic card haven't use the full bandwidth of 2.0 x16 or 2.0 x8 slots yet.

http://www.techpowerup.com/reviews/AMD/HD_5870_PCI-Express_Scaling

In this link, techpowerup use 1 Radon HD 5870 and tested all the difference Pci-e sizes (x1, x4, x8, and x16 2.0s)

From there results pci-e 2.0 x8 seams to be the bandwidth most graphic cards are using. There little difference going up to x16.