Hello

There is not a supported configuration to use all of the modules. The R620 does support the flexible memory configuration feature. The flexible memory configuration feature allows you to use unsupported memory configurations. Normally, if you did not populate the memory in a supported configuration the system would disable memory to attempt to create a supported configuration.

You shouldn't mix memory within a group, and the A and B lanes should be identical configurations. There are three memory groups spread across 4 channels on each lane. The groups are 1-4, 5-8, and 9-12. A supported configuration would be 16GB modules in 1,2 and 8GB modules in 5,6 and 9,10. The configuration would be the same on both A and B. The memory population rules are in the system manual.

http://www.dell.com/support/

Thanks