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I have this motherboard with 2 PCI-E Graphics cards, apparently only one of them is actually x16 what ever that means.

http://www.gigabyte.com/products/product-page.aspx?pid=2625#ov

If I put the same graphics card in each slot, will I get a performance boost in games? (I belive SLI is not supported on this board, although the card I have do support it)

This is the video card I have and I was going to get another one.

http://www.gigabyte.eu/products/product-page.aspx?pid=2804#ov

And can someone please explain the difference between "PCI-E 16 x4" and "PCI-E 16 x16"?

Thanks heaps.

UPDATE:

Performance Mark Tests showed 10FPS in Complex 3D tests on the x4 Slot and 57+ FPS on the x16 slot.

Nothing else really differed.

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I've used a second card mostly as physx and to do processing for a secondary display. –  HTDutchy Apr 2 '12 at 13:13
    
Can you set which card is used for PhysX? –  Ezra Apr 2 '12 at 13:42
    
Yes if you open the nvidia control panel and go tot the physx settings you can choose what cpu or gpu to use for physx, either the cpu, gpu1, gpu2, etc. as far as I know you can't select multiple –  HTDutchy Apr 2 '12 at 13:55
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Unless you need more than 2 monitors adding a 2nd low end card is generally not a good option. compared to single card that has double the performance. SLI/xFire overhead means that two cards are almost never twice as fast as a single card even in the best case. In the worst case you get almost no improvement (typically games without a SLI/xFire profile from nVidia/AMD). –  Dan Neely Apr 2 '12 at 14:22
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2 Answers 2

up vote 8 down vote accepted

Some games can use a dedicated card for PhysX simulation.

Other than that, I can't come up with anything that the second card could be used for (in terms of enhancing performance).

The difference between x1, x2, x4, x8 and x16 PCIe is the maximum throughput of the bus (how much data can pass between the card and the rest of the system in a given time).

Directron lists the following speeds:

PCI Express 1x   250 [500]* MB/s
PCI Express 2x   500 [1000]* MB/s
PCI Express 4x  1000 [2000]* MB/s
PCI Express 8x  2000 [4000]* MB/s
PCI Express 16x 4000 [8000]* MB/s
PCI Express 32x 8000 [16000]* MB/s

* Note 1 - Since PCI Express is a serial based technology, data can be sent over the bus in two directions at once. Normal PCI is Parallel, and as such all data goes in one direction around the loop. Each 1x lane in PCI Express can transmit in both directions at once. In the table the first number is the bandwidth in one direction and the second number is the combined bandwidth in both directions. Also please note that in PCI Express bandwidth is not shared the same way as in PCI, so there is less congestion on the bus.

Update: Table above contains speeds for PCI Express 1.0 bus. For version 2.0, multiply all bandwidths by 2. For example a PCI Express 2.0 16x slot has a max bandwidth of 8000 MB/s one way or 16000 MB/s both ways.

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So a PCI-E X16 Slot can run at X4 and X16? –  Ezra Apr 2 '12 at 11:21
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If they have matching PCI-E version supported i.e 1.1 2.0 3.0 etc. –  ZaB Apr 2 '12 at 11:32
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Short answer for doubling up cards (without SLI) for performance boost in games = No, you won't get any. One card will sit idle while the other does all the work! :) –  HaydnWVN Apr 2 '12 at 11:40
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@Ezra To my understanding, yes (under the conditions that ZaB noted). There seems to be some backwards-compatibility between some revisions, but, personally, I have never had any compatibility issues with PCIe, so I don't know how relevant it is. –  Oliver Salzburg Apr 2 '12 at 11:40
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@Ezra it's the difference between mechanically and electrically 16x. The number of PCIe lanes is limited by the chipset; except on high end models there aren't enough lanes provided by intel/amd to have 2 slots running at 16x electrical. Designing a board that can switch between 16/4(or 1)x with a single GPU and 8/8 with two GPUs adds complexity and cost to the design. Also IIRC some lower end Intel chipsets don't support SLI/xFire which greatly reduces the utility of dual cards. Fortunately very few games actually push enough data on the PCIe bus for running at 4x to really hurt. –  Dan Neely Apr 2 '12 at 14:17
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The motherboard support CrossFire, which is a brand name for SLI between 2 ATI (AMD) videocards. Your current videocard is an NVidia one, and indeed doesn't support CrossFire.

As for the slot sizes, PCI-e is intentionally designed to allow imperfect combinations. For instance, as a rule a 16x videocard will still work (with lower performance) in a 4x slot. Your motherboard has an example of such a 4x slot. Now, why is it just as big as the other, 16x slot? That's because many of those videocards are big, heavy monsters. Using the mechanical format of a 16x slot prevents the card from falling out.

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