I'm trying to find out how memory is arranged in dual channel mode, i.e. which memory addresses are on which DIMM. What I have currently found out is that there are two modes "ganged" and "unganged" and that there is little difference between them performance-wise.
With ganged mode I understood that each 128-bit word is split in a two 64 bit words, and those are combined when read / written using two channels at the same time. That would mean that for every 128 bits one would probably contain the lower 64 bits (/8 bytes) and the other the higher 64 bits. So byte addresses 0-7 are on one DIMM, and the next 8-15 are on the other. Is this correct?
What's entirely unclear to me is how memory is arranged in "unganged" mode. Is the memory still spread over the two modules using "sectors" of a specific size? Or is another scheme used?
Do these arrangements differ per processor or is this kind of operation standardized somewhere?
