SLI question

[Randluin]

When putting 2 pci express cards in a motherboard what is the restriction? I mean do they both have to be the exact same thing?

I know u can't mix a geforce with an ati, but what about speed do they have to both vbe the same speed or what. I'm just curious.

[Midknyte]

did you look at the links on best of video??
http://www.sysopt.com/forum/showthread.php?t=162277

you need two cards of the same GPU core. newer drivers allow you to use two different vendors, but they have to be the same core.