Linux: Check Ram Speed and Type

How do I check RAM speed and type (line DDR or DDR2) without opening my computer? I need to purchase RAM and I need to know the exact speed and type installed. How do I find out ram information from a shell prompt?

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 0x0018, DMI type 17, 27 bytes
Memory Device
        Array Handle: 0x0017
        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: 0x2CFFFFFFFFFFFFFF
        Serial Number: 0x00000000
        Asset Tag: Unknown
        Part Number: 0x5A494F4E203830302D3247422D413131382D
Handle 0x001A, DMI type 17, 27 bytes
Memory Device
        Array Handle: 0x0017
        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

You can just grep speed and skip all the details:

 
dmidecode --type 17  | grep -i speed
 

Sample outputs:

 Speed: 1333 MHz (0.8 ns)
 Speed: 1333 MHz (0.8 ns)