175a9a62_al_com___Memory_terms_glossary__Description
[Title] DDR, DDR2, DDR3 [Description] 
DDR stands for double data rate and is a type of memory technology. Almost all modern computers run on the newer versions of DDR (DDR2 and DDR3), which offer faster speeds and additional capacity than the original DDR. DDR-based technology is not backwards compatible, so if a system is designed to use DDR3 memory, it can only use DDR3 memory. To find out which kind of memory your system is designed for, use the free Crucial System Scanner tool on our website.
Crucial.com - Memory terms glossary
Description