The dmidecode command gives you all informations available about your memory.
With the special parameter “-t 16″, you can see the maximum (physical) memory that your server can have:
$ dmidecode -t 16
# dmidecode 2.8
SMBIOS 2.4 present.

Handle 0×1000, DMI type 16, 15 bytes
Physical Memory Array
Location: System Board Or Motherboard
Use: System Memory
Error Correction Type: Multi-bit ECC
Maximum Capacity: 32 [...]