Q. What are the differences between DDR3 and DDR2 RAM? I’m planning to add more memory to my computer. I’ve heard that DDR3 is faster. But is it worth the extra money?

A. There are several types of double data rate (DDR) RAM. DDR has been around since 2000. The original is sometimes called DDR1.

DDR2 was introduced in 2003. It took a while for DDR2 to reach widespread use. But you’ll find it in most new computers today. DDR3 began appearing in mid-2007. The numbers refer to the generation.

First off, the different types are not interchangeable. The RAM must be compatible with your memory controller and motherboard.

If the processor is from Intel, the memory controller is part of the chipset, on the motherboard. AMD processors have integrated memory controllers. Motherboards are designed for use with particular processors.

Additionally, AMD does not yet support DDR3. Support should come during 2008.

RAM modules contain a notch. The notch guides the module into the motherboard’s RAM slot. DDR, DDR2 and DDR3 have notches in different locations. The different types of DDR RAM also have different numbers of pins.

It’s impossible to install a module on the wrong motherboard.