  A1,A2,A3,B1,B2,B3 = 8GB DDR3 1600Mhz ECC RDIMM (low volt, single or dual??) A4,A5,A6,A7,B4,B5,B6,B7 = 4GB DDR3 1333Mhz ECC RDIMM (low volt, single rank) for a total of 80GB of RAM.   It would be 72GB, there is no slot 7. There are 6 slots on each lane.   The rank will not matter unless you get quad rank DIMMs. If you get quad rank modules you may not be able to use all of the slots. I would have to check the population rules regarding quad rank modules to be sure.   They can be single or dual, but all memory within a bank should be identical, including rank. Thanks
Hello, I have a dual-processor PowerEdge R520, and I want to upgrade the memory, while retaining as many of my existing DIMMs as I can (all, preferably!). It currently has 32GB in 8x 4GB ECC DDR3 RDIMMs,1333MHz low volt single rank (Dell-331-4422). I'm looking at adding 2x 16GB ECC DDR3 RDIMMs, 1333 MHz  low-volt dual rank, PC3-10600. The R520 has three memory channels per processor, supporting up to 12 DIMMs I'm looking at the document ps2q09-20080414-Benson.pdf regarding Dell R520 memory configuration, but it's not clear to me how I should plan to configure the memory modules I have, or whether this upgrade is a good choice. Can I mix 16GB and 4GB DIMMs in the same channel? Which channel should use the larger DIMMs? Should I plan to purchase all new DIMMs if I want to increase the memory to 64GB? Can you advise?  Thanks!
PowerEdge R520 mixed memory configuration