This is discussed many times before, but without definitive answer. What is the correct way to arrange 16GB of additional memory? By default, the iMac has got 8GB of memory installed in a 4/0/4/0 way, or: BANK0/DIMM0 4GB BANK0/DIMM1 Empty slot BANK1/DIMM0 4GB BANK1/DIMM1 Empty slot Now, some people advice to add 16GB in the empty slots, making it 4/8/4/8, or: BANK0/DIMM0 4GB BANK0/DIMM1 8GB BANK1/DIMM0 4GB BANK1/DIMM1 8GB Others say the banks must have equal memory in their DIMMs, making it 4/4/8/8, or: BANK0/DIMM0 4GB BANK0/DIMM1 4GB BANK1/DIMM0 8GB BANK1/DIMM1 8GB Does the memory have to be equal in the banks or in the DIMMs to run in dual channel mode? Also, some say it's better to have the higher capacities first, making it 4 possible combinations: 4/8/4/8 4/4/8/8 8/4/8/4 8/8/4/4 Which of these is the best configuration? And why?