X16x16x16x16 Graphics Review?

[omgthisnamesux]

I've seen the reviews of X16x8x8 vs. x16x16x16 for motherboards like the EVGA Classified/Asus P6T6 Workstation.

I've also read the quad-sli performance reviews (vs. gtx280 sli, and 4870x2 sli).
http://www.bit-tech.net/hardware/graphics/2009/01/08/nvidia-geforce-gtx-295-quad-sli-review/18

Anyways - my question is: Anyone know of any GTX295 vs. (X) Performance reviews on a motherboard that support x16x16x16x16. Like the P6T7 WS which has two NF200 chips
http://www.motherboards.org/reviews/motherboards/1913_3.html

 

[randomizer]

What is the point of 2 NF200 chips when they are trying to feed 2 16X slots into a 16 lane bottleneck with the X58 chipset?

 

[omgthisnamesux]

I was under the impression the bottleneck on x58 was 36 lanes for PCIex?

Also, I was under the impression that 99.9% of cards don't actually use more than 8 lanes, thus the 16x16x16 vs. 16x8x8 tests show that the second option is better performance (since the NF200 load balancing in the first configuration is not needed, and slows the system down, due to people running the tests with cards that don't use more than 8).

The NF200 bypasses the forced bandwidth configuration - meaning just because a PCIex lane is flagged as 16x coming in, the NF200 translates it into actual used lanes going out. So if your card doesn't use full 16x, it doesn't deduct 16 from the 36 lane bottleneck - instead it will use the actual amount of lanes used.

Really, I guess my question is How do I find out how many lanes a graphic card actually uses? I've read that 295's are the only cards that use more than 8 lanes, i've read that 285's don't even use 8 lanes etc..etc.. but I've never really seen an actual break-out of lanes per card - or have the knowledge to figure it out myself

Anyways - I am just trying to learn this stuff and readily admit I have little to no knowledge of how this works, my information above is from reading spec's and data (which is great for quoting, but shite for understanding)

 

[randomizer]

X58 has 36 lanes, which are normally divided into 16x-16x or 16x-8x-8x configurations. If you add a single NF200 chip you get an extra 8 lanes to the slots, so you can run 16x-16x-16x at the slot, but the connection between X58 and NF200 is still only 16 lanes, so 2 of those slots are being funnelled through a single 16x link.

Now as I understand it NF200 does some funky processing that is supposed to reduce that bottleneck, but even so there doesn't seem to be any performance benefits (if anything, there is a slight drop). Tom's Hardware did a short test comparing 16x-16x-4x, 16x-8x-8x and 16x-16x-16x fairly recently with 3xGTX285s: http://www.tomshardware.com/reviews/eclipse-plus-n200,2332.html

I don't quite understand what 2 NF200 chips will do. I don't know the details of the implementation, but a quick mental picture leaves me thinking that you'll end up trying to funnel 64 lanes into 2x 16 lane connections to the X58 chipset with 4 lanes left over. Even if not every card is using 16 lanes, with 4 cards that's a lot of bandwidth usage for only 32 lanes to the chipset.

 

[B-Unit]

When we say a card 'only uses' a certain number of lanes, the terminology is a bit misleading. All PCI-E Graphics cards are designed to use 16 lanes, however they dont all need that much bandwith to deliver full performance. When we say 'only uses' that means you can reduce its bandwith to x8 or x4 and not see a drop in framerates.

In essance, your interpretation of what the nForce200 chip does is flawed in that the chip cant tell how many lanes are needed for the GPU to see full performance. All it can tell is how the motherboard manufacturer has defined the PCI-E slot (x16 or x8). In order to tell how little bandwith a given card can get by on, you would need to find reviews where this is tested (few and far between)

If your adventurous, you can do this yourself with some masking tape and a little time on Google.

 

[omgthisnamesux]

Ah - understood.

So, I guess at the end of the day, there really is no benefit to a motherboard like the P6T7 WS:
http://www.motherboards.org/reviews/motherboards/1913_3.html

I had read some reviews about it, and people said it was good for gaming - but it seems like the only bonus is the 7th PCIe slot, and the 2 NF200 chips - and I couldn't tell if the 2 chips were actually worth it or not.

Thanks much for the responses, and for dealing with my minimal understanding of things