Cross firing on 2.0 and 3.0 pci x16 slots?

Nic7 · Jun 27, 2014

I'm new to pc building. I was wanting to get a second R9 280x for my build and crossfire them on the (h97 plus atx). The thing is only one of the slots is 3.0 the second one is 2.0. Does this matter? Will performance be hurt severely by this? Thanks.

TechyInAZ · Jun 27, 2014

Unlike SLI, CrossfireX is the only one that can crossfire two or more gpus using both 3.0 and 2.0.

However, I suggest looking up your mobo on the web to absolutely make sure it does support crossfireX.

Nic7 · Jun 27, 2014

TechyInAZ :

It says it supports crossfire. I just don't know if it will be poor or something.

ezskills · Jun 27, 2014

Yes you can but.... That board is technically CrossfireX capable, but the PCIE 2.0 slot is limited to x4 speed. Essentially, the card in the 3.0 slot would have the maximum x16 PCIE-3.0 bandwidth allotted by the Intel H97 chipset, but the bandwidth of the card in the 2.0 slot would be lessened quite a bit in comparison. Such a setup wouldn't achieve ideal Crossfire performance, but there would be a gain in performance. Typically, you can expect a R9 280x Crossfire configuration to scale upwards of 70- to 90-percent (sometimes nearing 100-percent) in many titles. A Crossfire setup using your motherboard would not yield the same levels of Crossfire scaling due to the slightly limited bandwidth of the 2nd card.

What you'd ideally want for a Crossfire or SLI configuration is a board that has two identical x16 slots, which would then split the x16 into a x8 + x8 configuration. MSI's Z77A-G45 and above boards have such a setup - they all use two PCIE-3.0 x16 slots. (So do many boards from other manufacturers.)

Lastly, you could potentially run into further bandwidth limitations for the 2nd card since it shares its 4-lanes (x4) with the remaining PCIE-x1 slots. Should you make use of additional cards in those slots, you would end up taking away some of the already slightly limited bandwidth.

Martell1977 · Jun 27, 2014

It will likely limit both cards to the 2.0 spec, which from what I read shouldn't be a problem since current GPU's cannot saturate a PCIe 2.0 slot as of yet.

Nic7 · Jun 27, 2014

ezskills :

Yes you can but.... That board is technically CrossfireX capable, but the PCIE 2.0 slot is limited to x4 speed. Essentially, the card in the 3.0 slot would have the maximum x16 PCIE-3.0 bandwidth allotted by the Intel H97 chipset, but the bandwidth of the card in the 2.0 slot would be lessened quite a bit in comparison. Such a setup wouldn't achieve ideal Crossfire performance, but there would be a gain in performance. Typically, you can expect a R9 280x Crossfire configuration to scale upwards of 70- to 90-percent (sometimes nearing 100-percent) in many titles. A Crossfire setup using your motherboard would not yield the same levels of Crossfire scaling due to the slightly limited bandwidth of the 2nd card.

What you'd ideally want for a Crossfire or SLI configuration is a board that has two identical x16 slots, which would then split the x16 into a x8 + x8 configuration. MSI's Z77A-G45 and above boards have such a setup - they all use two PCIE-3.0 x16 slots. (So do many boards from other manufacturers.)

Lastly, you could potentially run into further bandwidth limitations for the 2nd card since it shares its 4-lanes (x4) with the remaining PCIE-x1 slots. Should you make use of additional cards in those slots, you would end up taking away some of the already slightly limited bandwidth.

Thanks for telling me this, I luckily haven't bought the board yet, i was only minutes away from ordering it. i'll look for double 3.0 then.

Ended up going with the z97 asus.

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