Hello. How many CPUs do you have installed?  There are many memory population guidelines including having memory across all channels balanced for optimal performance. For one CPU, you will only be able to make use of six modules due to this limitation, hence: A1,A4, A2A5, A3A6: 2GB with total memory capacity of 12GB For two CPUs: A1A4, A2A5 & B1B4, B2B5: 2GB, gives memory capacity of 16GB. I would recommend using higher capacity memory modules like 4GB, 8GB or even 16GB as they offer more and robust memory expansion. 
Hi, I have a T610 with 8GB (4x  PC3-8500R 2G 2Rx8) . I would put more 8GB, (4x  PC3-10600R 2G 2Rx8). Works? What is the best setting?  []'s
Dell PowerEdge T610 memory upgrade?