What does PCI Express 2.0 16x slot (@x4) mean?

Looking to Crossfire two 7970's, but im a little confused with my motherboard's specs!


one slot is 3.0 @x16 whilst the other is 2.0 @x16 (@x4). what does this mean? is the second slot slower? Will crossfire not be as good of performance as shown in benchmarks? Am i better off with a single GPU in the 3.0 slot?

Thanks in advance!
8 answers Last reply
More about what express slot mean
  1. This means that your second pcie slot will only work with a pcie card x1 to x4, if your second video card needs a x16 than it will unlikely work, however if it does it will be considerably slower
    EDIT: you are better of using the 3.0 pcie, it will be a lot faster
  2. a pci-e 3.0 is not really faster, esp if you dont have a high end GPU. but a 4x at pci-e 2.0 is limited in bandwidth in todays standards.
    8x of pcie 3.0 is ok
  3. So really, a crossfire setup is a bad idea on this motherboard?? I won't get that full crossfirega effect as only one of my pci-e slots will allow full power while the other card will only run at like 20% of what its capable?? That sucks, I should have bought a different board. I don't really wanna go crazy and get the gtx 690, but its hard to find a really powerful card that uses one slot!

    Any suggestions? I'm looking to run max settings @ a steady 60fps on 1080p. Most games the crossfire would have been overkill I know, but on the most demanding games it would be nescescary for 60fps(crysis 3 I can only run on medium on a gtx 480 and get like 40fps avg)
  4. Means that the first slot is Gen3 and has the full 16 lanes (16x) behind it.
    The second is a Gen2 slot with a 16 lane connector, but in actuality there are only 4 lanes (4x) wired up to it electrically.

    A Gen3 lane has double the bandwidth of Gen2 lane, so to translate the top slot into Gen 2 terms, it has an equivalent 32x of bandwidth.

    Yea, that board isn't suitable for Crossfire/SLI. PCI-2 8x is the minimum you need to not bottleneck a graphics card.

    Get a 7970, that will run in that 16x slot just fine and it has the best chance of maxing out Crysis 3 of all cards, unless you want to shell out for a 690 or a Titan.
  5. You will drop in performance but nowhere near only 20% of performance, likely lose about 30ish % perf (pulling this out of the air from random review I can't find anymore)

    a single 7970 can amx out most games @ 1080P though
  6. Plus, with a second card in the motherboard, the first slot will only run at X8 anyway.
  7. Ok guys thanks, all great answers. This is why you don't cheap out on motherboards :\..

    since i'm going to be getting a single GPU, whats the best single GPU(besides the monsters GTX 690 & 7990)

    i assume either the GTX 680 or 7970, any specific make/model i should be looking at? Reading forums, it looks as if the 7970 GHz cards are faster than the 680's. This is the fastest clocked card for the price


    I'd be ordering from newegg.ca or tigerdirect.ca just looking for the best deal now.
  8. Here is a good overall list but includes all vendors
    7970 clocked @ 1ghz are as fast as 7970ghz @1ghz, just that hte 7970ghz can OC more


    I personally grab this card

    What case are you running, wanna make sure you can fit it in properly
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