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Is PCI express 3.0 backwards compatible with the other revisions? I read on Wikipedia that this was going to be attempted, but I can't find anywhere this is confirmed.

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closed as off topic by MDMarra, Ward, Chris S, Zoredache, Shane Madden Nov 28 '11 at 1:43

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1 Answer 1

Yes. The cards and bus (per card) will operate at the lowest common speed that both support.

Wikipedia: PCI Express mentions that it would be backwards compatible with existing PCIe implementations.

PCIe 3.0 Base Spec §4.2.2 elaborates:

For backwards compatibility, the Link initially trains to L0 at the 2.5 GT/s data rate using 8b/10b encoding as described in Section 4.2.1, then when the data rate is changed to 8.0 GT/s or higher, 128b/130b encoding is used.

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Cool, do you have a source for this information? I can not seem to find it anywhere... –  prolink007 Nov 28 '11 at 0:19

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