The main difference between DDR2 and DDR3 RAM apart from different operating voltage is the positioning of keynotch. DDR stands for double data rate
Second important value to notice is the frequencies / speed
frequency of DDR2 ranges from 400 MHz, 533 MHz, 667 MHz, 800 MHz,1033MHz. It can be over-clocked up to 1250MHz.
frequency of DDR3 is 800 Mhz, 1066 Mhz, 1330 Mhz, 1600 Mhz it can be overclocked maximum upto double.
Main advantages of DDR 3 are:-
- The higher bandwidth thanks to 8 bit prefetch buffer,
- Data transfer at the effective clock rate of 800–1600 MHz
- Higher performance at low power (longer battery life in laptops)
- Improved design