Stands for "Double Data Rate Type 3." DDR3 is an SDRAM specification introduced in 2007. Compared to previous DDR2 standard, DDR3 uses 30% less power and provides significantly faster data transfer speeds.
DDR3 memory modules are available in both DIMM and SO-DIMM form factors. DIMMs are commonly used for desktop PCs, while SO-DIMMs are typically used for laptops and all-in-one computers. While DDR3 DIMMs and SO-DIMM are the same size as their DDR2 counterparts, they are not compatible with DDR2 RAM slots. Fortunately, the connecting pins are arranged differently, so it is physical impossible to insert a DDR3 memory module into a a DDR2 RAM slot, and vice versa.
Several types of DDR3 memory exist, providing a range of maximum data transfer rates. The first version of DDR3 memory, called DDR3-800 (also "PC3-6400") provides peak transfer rates of of 6,400 MB/s. Other specifications include DDR3-1066, DDR3-1333, DDR3-1600, DDR3-1866, and DDR3-2133. DDR3-2133 (also called PC3-17000) supports peak transfer rates of 17,067 MB/s.