DDR2 DIMMs are not designed to be backward compatible with DDR DIMMs. 
The notch on DDR2 DIMMs is in a different position from DDR DIMMs, and 
the pin density is higher than DDR DIMMs in desktops. DDR2 is a 240-pin 
module, DDR is a 184-pin module. Notebooks have 200-pin modules for DDR 
and DDR2.
-Pete


Tom Waddell wrote:
> I have an older computer with an MSI motherboard. The board only lists DDR memory as being compatible. When I pulled the memory out of the computer I discovered it was DDR2. Systen recognized the memory. My guess is DDR and DDR2 are interchangeable. If not, my guess it should not have worked in the MB but it did. Any thoughts. 
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