What is the difference between DDR3, DDR2, DDR, and SDRAM?

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What is the difference between DDR3, DDR2, DDR, and SDRAM?


Most desktops and notebooks use one of four popular types of dynamic random access memory (DRAM) for the main system memory.

Single data rate (SDR) SDRAM is the older type of memory, commonly used in computers prior to 2002.

Double data rate (DDR) SDRAM hit the mainstream computer market around 2002 and is a straightforward evolution from SDR SDRAM. The most significant difference between DDR and SDR is that DDR reads data on both the rising and falling edges of the clock signal, enabling a DDR memory module to transfer data twice as fast as an SDR memory module.

Systems implementing the follow-on technology to DDR, called DDR2 began to appear in mid-2004. DDR2 achieves speeds beyond that of DDR, delivering bandwidth of up to 8.5 GB per second. Frequently, DDR2 based systems can use memory installed in pairs to run in "dual channel mode" to increase memory throughput even further.

The latest generation of memory technology, DDR3, began to appear in systems in late 2007. DDR3 is an evolutionary step beyond DDR2 and operates at lower voltages, thereby consuming less power, and can transfer data at rates up to 12.8 GB per second. Typically, DDR3 based systems can address memory modules in banks of 1, 2 or 3. If a system supports it, installing memory in matched sets of 2 or 3 modules (dual channel or triple channel modes) will deliver greatly increased memory performance over running a single memory module by itself.

Generally speaking, motherboards are built to support only one type of memory. You cannot mix and match SDRAM, DDR, DDR2, or DDR3 memory on the same motherboard in any system. They will not function and will not even fit in the same sockets.

The right type of memory to use is the one that your computer takes! The easiest way to find the right memory for your computer is to look up your system in Crucial's Memory Advisor tool. The Memory Advisor tool will list only compatible memory for your system.

If you don't know the exact model of your computer, the Crucial System Scanner can scan your computer hardware to automatically detect your system configuration and give you a report on which upgrade is right for you.


Kilobyte Kid

Currently, I have (2) 1GB Memory Modules.  The specifications are:  DDR-SDRAM, Non-ECC, 333MHz, 200pin SODIMM.


I am told by many that I cannot upgrade to (2) 2GB Memory Modules.


Why not?


What will go wrong?


All input welcome.



Moderator Moderator

It is very difficult to answer your questions without knowing more about your system. If you run the System Scanner that is linked in the article, it will identify your computer and make recommendations for ugprades, as well as telling you the maximum amount of memory you can upgrade to.


If you have questions about the System Scanner results, contact Customer Service for your region and they will be able to help you.