I think you're confusing terminology here...
The "3" in DDR3 does not mean there are three streams of data traveling between CPU and memory. That depends on the motherboard, memory controller, and how the memory slots are populated.
A memory module is just a place to store things. The decisions made on when and how data gets from point A to point B are made elsewhere.
What you're probably thinking of is ganged vs unganged mode, which has to do with how each channel talks with its memory controller. In ganged mode, the channels are synchronized and send data to the CPU in a big block. In unganged mode, each memory controller is free to operate independently from the other.
In terms of software, it helps to be aware of these lower details in order to avoid doing something boneheaded, but in general they're hidden and programmers have little or no direct control on when and how they happen.
Do not meddle in the affairs of archers, for they are subtle and quick to anger.
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