TheServerNinja,   The C6220 supports Registered ECC DDR3 DIMMs (RDIMM), low-voltage DIMMs (LVDIMM), and load-reduced DIMMs (LRDIMM).   Hope this helps.  
Does anyone know if the Dell C6220 Gen 1 Servers will accept Load Reduced memory (LRDIMMs)?  Or will they only accept ECC Registered.  I am upgrading our system and would like to know before ordering.  We are putting in 32GB DIMMs.   Thank you for your time and consideration.
Dell C6220 Gen 1 - LRDIMMs