PCI Express x16 for SLI

[flameshad0w]

I've noticed that some motherboards with SLI support have 1 x16 card, while others have 2... What's the difference in this? and how would it work, if each SLI card requires a x16 slot. I think some people said the x16 one is divided into 2 x8's?

Specifically, what would the difference be between
http://www.newegg.com/Product/Produc...24#DetailSpecs
and
http://www.newegg.com/Product/Produc...82E16813131568
if I was using 2 Geforce 7900GT's?

[doctorgonzo]

You heard correctly: some SLI motherboards split the x16 connection into two x8 connections when two video cards are installed. Thus, if you have one video card installed in such a board, it gets the x16 bandwidth; if you have two video cards installed, they each get x8 bandwidth.

The A8N32-SLI Deluxe will provide both slots with x16 bandwidth. The "32" in the name comes from the fact that there are two PCI-E slots with x16 bandwidth; hence 32 total.

PCI-E is flexible in that the physical slot width and the PCI-E "lanes" available aren't rigidly tied together. A x16 PCI-E slot can actually use less than the full 16 lanes. Similarly, you can plug a x1 card into a x4 slot without problems, as the card will only use one lane.

[flameshad0w]

So is there any difference in when each card gets x8 bandwidth and when each card gets x16 bandwidth? Is there a reason to get the card with dual x16?

[doctorgonzo]

I don't know how big an impact this really makes, but there is a difference in terms of bandwidth available. A motherboard with 2 genuine x16 slots will give the video cards more potential bandwidth to use. You may want to search online for some benchmark results to see what kind of difference it really makes.

[rspassey]

ASUS claims it till yield up to a 10 % performance boost with the dual x16 PCI - E slots. If I were buying a new motherboard for my SLI rig, I would get the 32 version. Not only does it have the potential for better performance, it also have a better cooling solution, is quiter, and the entire design is 'newer' or revamped.