The difference between DDR2 and DDR3 lies in speed and in transfer rate. DDR3 is capable of running on speeds up to 1600 MHz on high transfer rates. Channels refer to the same memory banks of the same type installed on a computer. For example, if you have 2 x DDR2 2 GB memory banks, the computer will run with Double Channel on 128bit as the architecture sums up when Double Channel transfer rate is active. The same applies to Tripple Channel.