DDR3 SDRAM

In computing, DDR3 SDRAM, an abbreviation for double data rate type three synchronous dynamic random access memory, is a modern type of dynamic random access memory (DRAM) with a high bandwidth ("double data rate") interface, and has been in use since 2007...

It is the higher-speed successor to DDR and DDR2 and predecessor to DDR4 synchronous dynamic random access memory (SDRAM) chips.

DDR3 SDRAM is neither forward nor backward compatible with any earlier type of random access memory (RAM) due to different signaling voltages, timings, and other factors.

DDR3 DIMMs have 240 pins and are electrically incompatible with DDR2. A key notch—located differently in DDR2 and DDR3 DIMMs—prevents accidentally interchanging them.

Not only are they keyed differently, but DDR2 has rounded notches on the side and the DDR3 modules have square notches on the side. DDR3 SO-DIMMs have 204 pins. source.