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PCIe 2.0 Saturation

post #1 of 3
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Just curious, how close are video cards to saturating a 250MB/s PCIe 2.0 bus? Just want to know how soon the full 500MB/s interface to be included with the new Sandy Bridge mobos will be useful.
    
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post #2 of 3
That's 500MB/s per lane for PCI-E 2.0
16x slots have a bandwidth of 8GB/s.
I don't think it's saturated at all yet.
Kepler and Southern Islands might use PCI-E 3.0
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post #3 of 3
It really isn't enough to make a big difference. Check these analyses with modern graphics cards and see:

http://www.hardocp.com/article/2010/08/16/sli_cfx_pcie_bandwidth_perf_x16x16_vs_x16x8/
http://www.hardocp.com/article/2010/08/23/gtx_480_sli_pcie_bandwidth_perf_x16x16_vs_x8x8/
http://www.hardocp.com/article/2010/08/25/gtx_480_sli_pcie_bandwidth_perf_x16x16_vs_x4x4/

Even using the x4 slots doesn't show a huge penalty in performance, which means that we are nowhere close to even saturating the full bandwidth that's available. One of the biggest selling points of going with a 1366 platform over the 1156 was the fact that you get full x16 bandwidth on at least two of the PCIe slots, but as the above has shown (as well as a lot of real world user experience) the differences doesn't amount to the price premium if there is a strict budget in place.

Even though Sandy Bridge may bring wider bandwidth to the platform, I'm pretty sure any improvements in multi-GPU configurations is a result of the CPU just being better, overall, due to tweaks and optimizations that help in alleviating the overhead/bottleneck, while single GPU setups will see minor improvements.
     
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