Final word on the dual/triple channel memory config?

[Demigod Mac]

Now that the new Mac Pros are out, has anyone been able to determine how the channels relate to the memory configuration?

Right now I have three 2 GB sticks; I was thinking of tossing in another 2 GB stick for a total of 8 GB, but I'd rather not if it would revert it back to single channel. Dual is fine. Triple isn't all that necessary in real-world apps. Would four 2 GB sticks = dual channel?

[Umbongo]

Four is like dual channel but slightly faster.

[VirtualRain]

EDIT:

Umbongo is correct...

It appears MPG has some facts (http://macperformanceguide.com/Reviews-MacProWestmere-MemoryBandwidth.html)...

http://macperformanceguide.com/images/MacProWestmere2010/graph-memory-bandwidth.gif

This confirms that running 4 equal DIMM's offers between tri and dual channel performance. Which is also what AnandTech indicated (http://www.anandtech.com/show/2658/5):

In the four-slot configuration the first three slots correspond to the first three channels, the fourth slot is simply sharing one of the memory channels. The downside to this approach is that your memory bandwidth drops to single-channel performance as you start filling up your memory. For example, if you have 4 x 1GB sticks, the first 3GB of memory will be interleaved between the three memory channels and you'll get 25.6GB/s of bandwidth to data stored in the first 3GB. The final 1GB however won't be interleaved and you'll only get 8.5GB/s of bandwidth to it. Despite the unbalanced nature of memory bandwidth in this case, your aggregate bandwidth is still greater in this configuration than a dual-channel setup.

Real world performance difference:

http://macperformanceguide.com/images/MacProWestmere2010/graph-memoryspeed-modules.gif