There is probably a linux command similar to Windows' WMI that could query the memory information, but only 1GB and 2GB UDIMM's (Unbuffered/Unregistered) are supported in the T610, so it's more than likely that your 4GB DIMM's are RDIMM's (Registered), especially if they are the DIMM's that shipped from Dell.
Also keep in mind, that you must be running BIOS version 1.1.4 to use 16GB DIMM's.