What is the difference between DDR and ddr2 and ddr3?

The prefetch buffer of DDR2 is 4 bit(double of DDR SDRAM). DDR2 memory is at the same internal clock speed (133~200MHz) as DDR, but the transfer rate of DDR2 can reach 533~800 MT/s with the improved I/O bus signal. DDR2 533 and DDR2 800 memory types are on the market. DDR3 SDRAM(Double Data Rate Three SDRAM): read more

Additionally, DDR2 is capable of running at a lower voltage than DDR, and DDR3 is again capable of running at a lower voltage than DDR2. Update: Original question only asked about 1, 2 and 3, not 4. Finding details about DDR4 that can succinctly describe the difference isn't a particularly simple task. read more

DDR3 SDRAM(Double Data Rate Three SDRAM): DDR3 memory reduces 40% power consumption compared to current DDR2 modules, allowing for lower operating currents and voltages (1.5 V, compared to DDR2's 1.8 V or DDR's 2.5 V). The transfer rate of DDR3 is 800~1600 MT/s. DDR3's prefetch buffer width is 8 bit, whereas DDR2's is 4 bit, and DDR's is 2 bit. read more

There are several differences between DDR2 and DDR3 modules: DDR3 is not backwards compatible with DDR2. While both types of modules have similar numbers of pins, the notches in the PCB are in different locations. read more