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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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.
Chris S
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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 00:19