there is no compatability issues between pcie 1.0 and 2.1, the compatability issue lies in the BIOS, some older bios's dont like newer cards. I am currently running a pcie 2.1 card in a 1.0 slot as are many others. there are a few that report incompatabilities, which could just as easily be caused by their incompetence and lack of computer knowledge. The only way to "upgrade a pcie slot" is to replace the motherboard with a newer one. Just make sure you update the motherboard bios to the latest one, this is required for many older motherboards to work with new cards.