PCI-E 2.1 cards backwards compatible?

[Liet]

Might be a silly question, but I haven't upgraded cards in a while:

Will a PCI-E 2.1 card work in a 2.0 slot? Is 2.1 just a throughput improvement?

 

[mundane]

..

 

[Liet]

Thanks much. Been looking at 5870s, but the ones with larger (and I hope quieter) fans seem to all be PCI-E 2.1.