DDR2 SDRAM is an abbreviation for Double Data Rate 2 Synchronous Dynamic Random-Access Memory. So yeah, you can just call it simply as DDR2 RAM. It is used to replace DDR SDRAM but is then replaced by DDR3 SDRAM. On the other hand, DDR2 DIMMs are neither backward compatible nor forward compatible with DDR and DDR3 respectively.
Optimizing Power and Performance
DDR2 RAM can’t just double-pump data bus or the transfer of data on falling and rising edges of bus clock signal but also, it can increase bus speed while reducing power consumption.
It is able to do this by running internal clock at half speed of data bus. The integration of these results in total of 4 data transfer for every internal clock cycle.
Since DDR2 internal clock is running at half of DDR external clock rate, DDR2 memory is running at same external data bus clock that’s similar with DDR. This enables DDR2 RAM in providing same bandwidth but also, with better and improved latency.
To put it simply, DDR2 RAM is running twice the external data bus clock that of DDR2 can deliver. The speed of best DDR2 module is at least 2x of the best DDR memory module.