It has been just over two years since PCI Express replaced AGP as the predominant graphics interface for high-end 3D graphics. PCI Express offers considerably more bandwidth than AGP, 2.1GB/sec in AGP 8x versus 4GB/sec in an x16 PCI Express graphics slot (In addition, PCI Express is bi-directional, meaning that unlike AGP, data can simultaneously go in both directions, this effectively doubles PCI Express bandwidth.), but as we found with first-generation PCI Express graphics cards, the first wave of applications really weren’t designed to take advantage of the added bandwidth PCI Express provides.
What we’ve set out to do with this article is to take an updated look at PCI Express performance with newer titles than what we initially used a few years ago, since PCI Express first debuted in 2004 we’ve seen more shader-intensive titles like F.E.A.R. be introduced, as well as more demanding benchmarks like 3DMark 06. We’ll also be using NVIDIA’s SLI technology exclusively for this article; with two GeForce 7900 GTX cards connected together running in SLI mode at both 4xAA and 8x/16x Super AA modes at resolutions as high as 2560x1600, we should hopefully push the PCI Express interface a little more.
Since NVIDIA hasn’t produced an AGP variant of the GeForce 7900 GTX to this point, we won’t be comparing the performance of PCI Express to AGP in this article, instead we’ll be examining the difference in performance between the 8x and 16x flavors of PCI Express.
To test this out we’ve gathered nForce motherboards from ASUS, the P5N32-SLI SE Deluxe and P5NSLI, which support 8-lane and 16-lane PCI Express operation for SLI. While these motherboards are based on different chipsets, the nForce4 SLI X16 and nForce 570 SLI, the architecture of both is fairly similar, only the nForce4 SLI X16 chipset used on the P5N32-SLI SE Deluxe has more PCI Express lanes: 48 versus the 20 lanes on the nForce 570 SLI. As we found in our ASUS Core 2-ready motherboard roundup
, both motherboards perform similarly to one another under equal conditions, so we feel like we should be able to make valid performance comparison between the two.
We realize that there are a lot of you still out there with AGP systems and we’ve got an article in the works for you that should help in determining the best AGP upgrade path for you.
With PCI Express 2.0 set to debut next year offering twice the bandwidth of today’s PCI Express 1.0 devices, we’ll probably be running similar tests a year from now asking the same question all over again, but that’s for another day...