Are the most elaborate platforms really required to host the fastest GPUs, or can you get away with P55's lane-splitting scheme? As Nvidia’s latest graphics processors push 3D performance to new heights, we examine the interfaces needed to support them.
A mere seven months have passed since our most recent PCI Express scaling article showed modest performance differences between PCIe x8 and PCIe x16 slots. But it has been a very busy seven months!
The first salvo came when Nvidia’s much-delayed GeForce GTX 480 smoked AMD’s Radeon HD 5870 as the fastest single-GPU card on the market, and the mid-priced solution that followed showed the highest multi-GPU performance scaling we’ve ever seen.
Unfortunately, such an elevated degree of technological achievement is difficult to swallow for a motherboard reviewer, as it makes my earlier findings irrelevant to most users.

The focus of today’s question will center on you, the PC owner. Do you actually need an X58 platform to support the latest graphics technologies, or will something with fewer lanes suffice? MSI helped us to facilitate the answer with a single product, by producing an X58 motherboard that also has the x8 and x4 modes found on some P55 solutions.
We’ve already seen how X58 and P55 motherboards offer similar gaming performance when using a single x16 slot. And limiting ourselves to a single board allows us to focus exclusively on PCI Express lane width by eliminating every other variable. The name of that product is, of course, the Big Bang-XPower.
While it certainly doesn’t represent the P55 market’s moderate pricing, the XPower’s biggest liability becomes an asset for the purpose of today’s test. Its two PCIe 2.0 x16 slots are divided between up to three x16-length slots each, changing to x8-x0-x8-x8-x8-x0 modes when slots three and five are filled, and then to x8-x4-x4-x8-x4-x4 mode when slots two and six are filled. Thanks to MSI, we can now check x16, x8, and x4 transfer modes on a single motherboard, without using little fingers of tape to reduce the number of connections on the card itself.
- The PCIe Bottleneck?
- Test Setup And Benchmarks
- PCIe Scaling: 3DMark Vantage
- PCIe Scaling: Alien Vs. Predator
- PCIe Scaling: Call of Duty: Modern Warfare 2
- PCIe Scaling: Crysis
- PCIe Scaling: DiRT 2
- PCIe Scaling: S.T.A.L.K.E.R.: Call Of Pripyat
- PCIe Scaling Summary
- SLI Scaling: 3DMark Vantage
- SLI Scaling: Alien Vs. Predator
- SLI Scaling: Call Of Duty: Modern Warfare 2
- SLI Scaling: Crysis
- SLI Scaling: DiRT 2
- SLI Scaling: S.T.A.L.K.E.R.: Call Of Pripyat
- SLI Scaling Summary
- Conclusion

You spend unnecessary $$$ on a x58 platform while I save money that I can put towards a GPU upgrade with my p55 platform
The first article tested CrossFire scaling with three 5870's:
http://www.tomshardware.com/reviews/p55-pci-express-scaling,2517-2.html
1.) It appears that the GTX 480 runs out of CPU faster than the HD 5870. 2.) It also appears that the biggest difference between games is how hard they hammer the GPU, based on details, lighting effect, etc.
3.) The result is that you're seeing an FPS cap from either the board or the CPU as the load shifts away from the GPU to other components. The good news is that this "cap" is higher than the "minimum playable" frame rate most people can tolerate, in most games.
So, what does this have to do with your question? The HD 5970 uses a PLX Bridge: http://www.tomshardware.com/reviews/radeon-hd-5970,2474-2.html
Both GPUs get the same data, and the PLX Bridge simply doubles it from one set of lanes to two GPUs. So, an x16 slot turns into two identical x16 sets, or an x8 slot turns onto two identical x8 pathways. The PCIe "bottlenecking" data you get for two 5870's should therefore be identical to the PCIe data you get from one HD 5870 x2, such as the Asus ARES, which is actually a faster card than the HD 5970.
You spend unnecessary $$$ on a x58 platform while I save money that I can put towards a GPU upgrade with my p55 platform
anyone know if 4850's are going to be unavailable any time soon? You could get the 3000 series for quite awhile after the 4000's released so I'm crossing my fingers until i can afford a cpu upgrade and another 4850
cpu is currently a 7750BE and so im pretty sure it would bottleneck the 4850's. I think it does with just one actually.
It's not the game's fault. The GPU can only go as fast as it was made to go. So in simple terms you could say that GPUs these days aren't "fast" enough to use all the bandwidth PCI Express offers.
On a card for card basis they are still quite a bit more powerful than the GTX 480 and should require the most bandwidth of any current card for maximum performance.
The first article tested CrossFire scaling with three 5870's:
http://www.tomshardware.com/reviews/p55-pci-express-scaling,2517-2.html
1.) It appears that the GTX 480 runs out of CPU faster than the HD 5870. 2.) It also appears that the biggest difference between games is how hard they hammer the GPU, based on details, lighting effect, etc.
3.) The result is that you're seeing an FPS cap from either the board or the CPU as the load shifts away from the GPU to other components. The good news is that this "cap" is higher than the "minimum playable" frame rate most people can tolerate, in most games.
So, what does this have to do with your question? The HD 5970 uses a PLX Bridge: http://www.tomshardware.com/reviews/radeon-hd-5970,2474-2.html
Both GPUs get the same data, and the PLX Bridge simply doubles it from one set of lanes to two GPUs. So, an x16 slot turns into two identical x16 sets, or an x8 slot turns onto two identical x8 pathways. The PCIe "bottlenecking" data you get for two 5870's should therefore be identical to the PCIe data you get from one HD 5870 x2, such as the Asus ARES, which is actually a faster card than the HD 5970.
Thank you for the explanation Crashman
I'm considering using the 4x on my mainboard for airflow reasons in my case and as of now, nothing seems to speek against it. I'm only using a lowly GTX 460 anyway.
The slower your CPU, the more the limit shifts from other components to the CPU. That means the maximum FPS will get dragged down even farther, making the 1680x1050 results look closer to the 1920x1200 results.