This type of RAM upgraded the Ram, DDR2 is, of course, with 3 features different :
1 - more bandwidth due to an increase in the rate of the clock ( clock rate )
2 - reduce the power consumption due to making different
3 - have the memory of a mediator ( Buffer ) speed fetch 8-bit

the difference, other that, Ram, DDR , DDR2, DDR3, there is power consumption all the DDR3 from the other two types, power consumption is less, while frequency more Also than they are. The greater the frequency, the higher the data transfer speed is also more. In addition, the low voltage in portable computer make, reduce heat, it gets the battery life it also increase.