I am looking at a variety of PCI Express cards, such as a SATA RAID Controller and a Video Card. Some of these cards say they only support PCI Express 2.1, not PCI Express 2.0. I know that my motherboard supports PCI Express 2-something, but the manual doesn't say '2.0' or '2.1'.

How can I tell if the PCIe slot on my motherboard is PCI Express 2.0 or PCI Express 2.1?

Is it possible to determine the PCIe type from the Windows or Linux commandline?

I was under the impression that most PCI Express 2.1 devices are backwards compatible with PCI Express 2.0. Is it possible that the vendor is wrong in saying that PCI Express 2.1 is required?