DDR, DDR2, DDR3 Transfer Rates

Just for reference here are the general speed ranges:

DDR: 200 - 400MBps [SSTL_2, 2.5 volts]
DDR2: 400 - 800MBps [SSTL_18, 1.8 volts]
DDR3: 800 - 1600MBps [SSTL_15, 1.5 volts]

In all cases a computer user does not care about the Interface standard or voltage level. Both translate into lower power requirements, but it's only a few watts. People with 100's of servers in a rack tend to care about the wattage.

The DIMM key is in a different location for each DDR type, so your system will normally only accept one style of DIMM. The key on the DIMM is a notch, or a free space with no pins.

Refer to http://www.interfacebus.com for more info.