From
Intel's site:
* Triple channel mode is enabled when identical matched memory modules are installed in each of the three memory channels (blue connectors).
* If only two of the blue memory connectors are populated with matched DIMMs, dual channel memory is enabled.
Their example board has 4 DIMM slots. If all 4 are filled it operates in dual-channel interleaved.
It really does seem that a multiple of 3 matched DIMMs is needed to enable triple channel. An even number of matched DIMMs puts it in dual channel mode, anything else and it falls back single channel.
Don't confuse banks and channels. A bank is a grouped set of memory slots. On dual or triple channel boards a bank will have 2 or 3 slots respectively. Additionally, a mutiprocessor board will have nodes which are made of one or more banks. Each node is local to one processor.
