What is DDR2 RAM? - Explained

Back and front of a DDR2 SDRAM.

DDR2 RAM came to live after the first generation of DDR RAM which was DDR1 RAM by superseding from DDR1 RAM in 2003. By gaining much computation speed in the DDR1 RAM from SDR RAM, computer scientists and engineers kept researching about enhancing the product capability.

What is DDR2 RAM?

DDR2 RAM is an enhanced and advanced version of DDR1 RAM which allows the computers to transfer data at double rate compared with SDR RAM. DDR2 RAM suspended the original standard which was in the DDR1 SDRAM and upgraded the specification which allows the DDR2 SDRAMs to make higher bus speed and require lower power by running the internal clock at completely half of the speed of the data bus. These factors was able to produce total four data transfers per internal clock cycle in DDR2 RAMs.

To over the come the issue which occurred by running at the half of the DDR external clock rate and same bandwidth with higher latency, DDR2 specification allows the DDR2 to operate at twice the external data bus clock rate which was able to provide the same latency which occurred previously.

The major key difference in DDR2 RAM and the standard version of DDR was the increase in the prefetch length. When DDR SDRAM had a prefetch length at two bits for every bit in a word, DDR2 SDRAM had four bits. With all the advancements, the voltage consumption in DDR2 SDRAM was 1.8V and it's lower which was 2.5V in DDR standard specification.

DDR1 SDRAM vs DDR2 SDRAM notch difference.

Just like in the DDR1 SDRAM version, the DDR2 SDRAM also continued the same versions of SO-DIMM also known as Small Outline Dual In line Memory Module and DIMM also known as Dual In line Memory Module. 

DDR1 SDRAMs were not possible to use in the DDR2 SDRAM capable main boards of the computer and DDR2 SDRAMS were capable of using in the DDR1 SDRAM compatible main boards. Which means the DDR1 is forward compatible and require only main boards which does have interfaces to DDR1 SDRAMs and DDR2 SDRAMs were not backward compatible which means the DDR2 SDRAMs require DDR2 compatible main boards with the interfaces.