You need to use biosdecode command line utility. Dmidecode is a tool or dumping a computer’s DMI (some say SMBIOS) table contents in a human-readable format. The output contains a description of the system’s hardware components, as well as other useful pieces of information such as serial numbers and BIOS revision. This command works under Linux, UNIX and BSD computers.
Open a shell prompt and type the following command:
$ sudo dmidecode –type 17
OR
$ sudo dmidecode –type 17 | more
Sample output:
# dmidecode 2.9
SMBIOS 2.4 present.
Handle 0×0018, DMI type 17, 27 bytes
Memory Device
Array Handle: 0×0017
Error Information Handle: Not Provided
Total Width: 64 bits
Data Width: 64 bits
Size: 2048 MB
Form Factor: DIMM
Set: None
Locator: J6H1
Bank Locator: CHAN A DIMM 0
Type: DDR2
Type Detail: Synchronous
Speed: 800 MHz (1.2 ns)
Manufacturer: 0×2CFFFFFFFFFFFFFF
Serial Number: 0×00000000
Asset Tag: Unknown
Part Number: 0×5A494F4E203830302D3247422D413131382D
Handle 0×001A, DMI type 17, 27 bytes
Memory Device
Array Handle: 0×0017
Error Information Handle: Not Provided
Total Width: Unknown
Data Width: Unknown
Size: No Module Installed
Form Factor: DIMM
Set: None
Locator: J6H2
Bank Locator: CHAN A DIMM 1
Type: DDR2
Type Detail: None
Speed: Unknown
Manufacturer: NO DIMM
Serial Number: NO DIMM
Asset Tag: NO DIMM
Part Number: NO DIMM
ref : http://www.cyberciti.biz/faq/check-ram-speed-linux/