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!

http://www.newegg.ca/Product/Product.aspx?Item=N82E16813128547

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

    http://www.newegg.ca/Product/Product.aspx?Item=N82E16814125439

    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

    http://ca.pcpartpicker.com/parts/video-card/#c=83,70,112&sort=a5

    I personally grab this card
    http://ca.pcpartpicker.com/part/gigabyte-video-card-gvr797oc3gd

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