Article ID : 00031002 / Last Modified : 07/23/2019Print

What is the difference between DDR, DDR2, DIMM, SODIMM, and MicroDIMM memory modules?

    DIMM, SODIMM, and MicroDIMM are all different types of Dual In-line Memory Modules. These memory modules consist of a number of memory components attached to a circuit board with gold pins on the bottom to provide a connection between the module and a socket on a motherboard. All are used to provide Synchronous Dynamic Random Access Memory (SDRAM) to a computer.

    Currently there are two standards for these various DIMM types: DDR (Double Data Rate) and DDR2 (Double Data Rate2). The DDR2 is essentially an upgraded version of the DDR standard that allows for memory modules with lower power consumption, greater heat dissipation, increased speed capabilities, larger memory capacities, and increased performance.


    • Though DDR2 modules have the same basic dimensions as DDR modules, they have different voltages and pin configurations. Because of these differences, DDR2 modules have a different key (a notch in the connector) to prevent them from being inserted into an incompatible socket. This means that DDR2 memory modules will only fit into computers with motherboards designed to support DDR2 memory and will not fit into computers with motherboards designed to support DDR memory modules.
    • Some memory modules also list a specification called CAS Latency (CL). CAS is an abbreviation for Column Address Strobe or Column Address Select. The CL number represents the number of clock cycles (time) needed for the memory controller to send a request to read a memory location and have the requested data sent through the module's output pins. The lower the CL number of a memory module (given the same memory frequency/speed), the better the computer will perform.

    This table illustrates the difference in the properties of the DDR and DDR2 memory modules:

    Property DDR DDR2 Difference between DDR & DDR2
    Voltage2.5 volts 1.8 Volts Lower power consumption and greater heat dissipation
    Size128MB to 1GB 256Mb to 4GB Larger memory capacities
    Speed200, 266, 333, and 400 Mhz 400, 533, and 667 Mhz Speed capabilities above 400MHz
    BandwidthUp to 6.4GB per second Dual Channel, up to 10.6GB per second Higher memory performance

    This table illustrates the different types of memory modules and the associated pin configurations for the DDR and DDR2 versions of those modules:

    Memory Type DDR2 DDR
    Unbuffered DIMM240pin 1.8V 184pin 2.5V
    Registered DIMM240pin 1.8V 184pin 2.5V
    SODIMM200pin 1.8V 200pin 2.5V
    Mini Registered DIMM244pin 1.8V N/A
    MicroDIMM214pin 1.8V 172pin 2.5V


    • An Unbuffered DIMM is a memory module designed for desktop computers and low end workstations.
    • A Registered DIMM is a memory module designed for network servers and high end workstations.
    • A SODIMM (Small Outline Dual In-line Memory Module) is a memory module with a smaller outline and thickness than standard DIMM modules and designed primarily for notebook computers.
    • A MicroDIMM is a memory module with a smaller outline and thickness than standard SODIMM modules and are designed for mobile type, slim type, and super lightweight notebook computers.