What happens when you stick your second GPU in an 8x slot
Subject: Graphics Cards | August 23, 2010 - 01:12 PM | Jeremy Hellstrom
Last Monday [H]ard|OCP investigated the performance differences between running a CrossFire/SLI system with both cards operating at 16x as opposed to one at 16x and one at 8x, which is more common on motherboards than true double 16x. The differences were so minute you almost had to squint to see them. Today they extend that testing by moving the second card into a PCIe slot that can only support 8x speeds. If you are wondering why someone would do that, the reason is cooling as using the 8x slot places that second video card further away from the primary GPU thus adding to your ability to cool them.
The first observation they made seems obvious, running both cards at 8x does indeed negatively affect performance but the second observation is less obvious and more valuable. Running the second card at 8x has no effect until you move to resolutions that require multiple monitors to reach at which point you begin to notice some negative effects, as you can see in their full review.
"In our continuing coverage of Multi-GPU configurations with varying PCIe Bandwidth, we put x16/x16 and x8/x8 PCIe to
the test. Does having less PCIe bandwidth make difference in gaming? We know that a "lesser" motherboard can save you
money. Using GeForce GTX 480 SLI we show you the real-world differences."
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