Backwards compatability with PCI express slots

Hello,
I have a motherboard with a PCI-E v1.0a compliant slot, will the newer 2.0 and 2.1 cards work in this slot?

Yes

PCI 2.0 x8 = PCI 1.0 x16, etc...

Hello and welcome to the forums
Yes PCI-E 2.0/2.1 is backward compatible with PCI-E 1.0

Just to be clear,

2.1 PCI-Express video cards may have issues working in 1.0 PCI-Express motherboard slots.

you can't use PCI-E 2.1 cards, that mean you can't buy any new ATI card. 80% motherboard will get trouble. try Nvidia card which should work. anyway buy them from local shop in case you need return them. I have returned 3 ATI card when I was trying to upgrade my GT8800 card

I believe backward compatible only mean you can put PCI-E 1.0 card in a PCI-E 2.0 slot and not vice versa

Right, except 2.0 cards can work in 1.0 slots, just not 2.1 cards in 1.0 slots.

The simple fact that I ran a pair of 8800GT's which are PCIe 2.0 cards on an ABIT AN8 32X motherboard which is PCIe 1.0/1.0, should blow that belief out of the water.

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Backwards compatability with PCI express slots

I meant that you can use a PCI-E 2.0 card in a motherboard which has PCI-E 1.0 slot

Yes i was talking about putting a 2.0 or 2.1 in a 1.0a slot, so it sounds like I should stick with an 2.0 card (tough to find a dual dvi 1.0 card anymore). I've typically stuck to ATI NVidia has given me problems, matter of fact the card I put in this motherboard was Nvidia (PCI) and caused a conflict with the PCI bus. Plugged in a borrowed ATI PCI card and no problems.