Lets set this straith.
Obviously some of you did no bother to follow the link I posted earlier.
Here it is again:
http://www.anandtech.com/mb/showdoc.aspx?i=2506
I am going to quote from the article:
The middle x16PCIe slot, colored yellow, is a single x16 PCIe slot.
For single video, you use the yellow x16 slot.
For dual video or SLI, you use the green slots (Outside two X8 PCI e Slots)
That is the only explanation.
What the review didn't say is that when SLI is in use the middle PCI 16x slot operates at a slower speed and can still be used.