What is the difference between PCIe 1 and PCIe 2?

[Zipp]

Hi guys,
I'm in doubt and need some help. I have a motherboard with PCIe-1 slot and was planning to by a graphics card which has 1GB memory and is backward compatibility. But as my understanding says PCIe-2 is double the speed of PCIe-1. So according to this my graphics card will only be 512MB. Is this right? Or any other help or explanation? Help me guys! I don't want to end up wasting my money...
Thanks

[Hardwareman]

The PCIe 1.0 bus runs at 1.25 GHz and has data rate of 250 MB/s.
The PCIe 2.0 bus runs at 2.5 GHz and has data rate of 500 MB/s.

In your case the memory of your PCIe-2 compatible graphics card will not decrease if you use it on PCIe-1 graphics card. It will be 1GB but all the difference would be in the actual performance. In realtime the difference is negligible. You cannot make out the performance difference that easily as it is too hard to make out...
All the best! Enjoy!

[deoWo]

Why care anyway? PCI-E 2.0 cards work with 1.0 and difference in performance is hardly noticeable! Go! Rock On!

[Fabian]

In theoretical bandwidth PCIe 2.0 is far better than PCIe 1.x. However, as long as the slot is running in 16x mode there is enough bandwidth even for a HD4870X2. I believe PCIe 2.0 also increases slot power which is good for low mid-range cards so that they don't need power connectors.

[Hardwareman]

Have a look on the Performance Test Comparision of Some GFX card on PCIe-1 and PCIe-2 Slots :

Now that difference is know as "Hardly Noticable"
Enjoy...!