How much bandwidth is exchanged on SLI cards?

[mvrx]

I've had an idea running around in my head for a different approach to adding multiple GPU cards (sli/crossfire style) to a system. But before my hypothetical idea should be posted, I'm curious if anyone have the actual GB/sec or gbit/sec numbers on just how fast these a dual/tri/quad SLI setup uses going across their retrofitted interconnect cables?

Also, how many pins does each link use?

Thank you.

 

[SunnyD]

I believe SLI is 8 bits each direction, however I have no idea at what frequency the SLI link runs.

I believe CrossFire doesn't require a bridge, and can use the PCIe bus itself.

 

[Bull Dog]

Modern, higher-end ATI cards use bridges.

 

[Fallen Kell]

Well, You start to see performance degradation when using less than a PCI-e V1.0 8X (4x 2.0) link as has been shown with several benchmarks. That means upwards of 4GB/sec of data is being sent to/from each card (2GB max in one direction, so 2GB/s to the card and 2GB/s from the card).