Originally Posted by
MacBoero
The channeling is within the motherboard chipset, and it only works when the adjacent memory modules in each channel match properly, hence the market for matched pairs of memory modules.
Not any more.
Modern Intel CPUs don't care whether the memory size is the same (I believe timings do still have to be the same). They'll use dual-channel access for as much of the RAM as they can, then drop back to single-channel for the rest.
Which does hit performance, but less so than running the two DIMMS in single-channel mode.