Educate me on PCI Express

[DWarrior]

OK, the standard for video cards is PCI Express x16, but after that I get throughly confused.

Let's say I decide to get the 30" dell and keep my 2 20", and according to my friend, getting a RAID Controller will help improve HDD performance (speed up PT operations).

That means I'd need 3 PCI Express x16 slots, right?

This motherboard has 3 PCI x16 slots

This one has 4, but it says "(at x16, x8, x16, x8)" in the text specs. Does that mean that 2 of the slots run at x8?

This board says "2 PCI Express x16 slots, compatible with PCI Express x8 Speed (Support SLI technology)". Meaning that there are 2 x16 that are also compatible with x8? What device would be manufactured for x8 but wouldn't run on x16?

I'm not looking for advice on which mobo to buy, just to clear up the confusion over the x16 and x8 stuff.