  DellR820,   I would suggest you populate the larger dimms first across the channels, so I would place the 64gb dimms in the slots with the white tabs, then populate all the remaining slots with the 32gb dimms.    Let me know if this helps.  
Hello, I have R820 (4 CPU's) with 32 32GB LR sticks (total 1024 GB). I am planning upgrade the server with 16 more 64GB sticks to achieve total server memory to 2048 GB. is it possible to achieve this configuration? if possible, can you please suggest where should I populate the new 64 GB sticks. Thanks in advance. Regards Venkat  
R820 DIMM Configuration (32 GB & 64 GB RAM sticks)