dmidecode コマンドを使ってハードウエアの情報が取得できます。 “-t memory” と指定すればメモリの情報だけを取得できます。
$ sudo dmidecode -t memory
# dmidecode 2.11
# SMBIOS entry point at 0xaaebdf18
SMBIOS 2.7 present.
Handle 0x000B, DMI type 16, 23 bytes
Physical Memory Array
Location: System Board Or Motherboard
Use: System Memory
Error Correction Type: None
Maximum Capacity: 2 GB
Error Information Handle: Not Provided
Number Of Devices: 2
Handle 0x000C, DMI type 17, 34 bytes
Memory Device
Array Handle: 0x000B
Error Information Handle: Not Provided
Total Width: 64 bits
Data Width: 64 bits
Size: 4096 MB
Form Factor: SODIMM
Set: None
Locator: SODIMM1
Bank Locator: Bank 0
Type: DDR3
Type Detail: Unknown
Speed: 1333 MHz
Manufacturer: Unknown
Serial Number: 00000000
Asset Tag: Unknown
Part Number: Not Specified
Rank: 1
Configured Clock Speed: 1333 MHz
Handle 0x000D, DMI type 17, 34 bytes
Memory Device
Array Handle: 0x000B
Error Information Handle: Not Provided
Total Width: 64 bits
Data Width: 64 bits
Size: 4096 MB
Form Factor: SODIMM
Set: None
Locator: SODIMM2
Bank Locator: Bank 1
Type: DDR3
Type Detail: Unknown
Speed: 1333 MHz
Manufacturer: Samsung
Serial Number: 00ACDF4C
Asset Tag: Unknown
Part Number: M471B5273DH0-YH9
Rank: 2
Configured Clock Speed: 1333 MHz