That would be correct;  with a single UDIMM in slot 1.    Channel A are slots 1 & 3, Channel B would be 2 & 4. Each channel must match in size and speed.  12GB of RAM is not a supported configuration in this server. 1, 4, 8, 16 and 32 GB are supported only.   Here are the memory specifications:   Regards,
I have Dell PowerEdge R210 II server with 4Gb of memory installed (one module). And I also have 8Gb memory module. I replaced 4Gb with 8Gb – server is working ok. But mixing memory in different ways got error "Unsupported memory configuration. DIMM mismatch across slots detected". Can I install them both to get 12Gb of memory? P.S. From server documentation: "Memory modules of different sizes can be mixed in sockets 1 to 4 (for example, 2 GB and 4 GB), but all populated channels must have identical configurations."
Dell PowerEdge R210 II mix memory