Hello 24GB is the maximum supported memory configuration when using UDIMMs. Populating slots 7,8,9 are not supported with UDIMMs. The memory population rules should be listed in the manual: www.dell.com/support/home/product-support/product/poweredge-r710/manuals Thanks
Have an R710 w/ 12x 2GB ECC Samsung RAM (M391B5673FH0 - 2GB 2Rx8 PC3 10600E 09 10 E1) installed in A/B 1/4/2/5/3/6 - 24GB total Recently acquired another 12GB (6x Hynix HMT125U7TFR8C 2GB 2Rx8 PC3 10600E 9 10 E0) I wanted to populated into A/B 7/8/9 - 12GB total However, populating these chips results in a non-responsive system - no POST - system powers up but no boot.Do I have the memory configuration wrong? 
R710 memory expansion problems