DDR2-SDRAM is high-performance main memory. Over its predecessor, DDR-SDRAM, DDR2-SDRAM offers greater bandwidth and density in a smaller package along with a reduction in power consumption. In addition DDR2-SDRAM offers new features and functions that enable higher a clock rate and data rate operations of 400 MHz, 533 MHz, 667 MHz, and above. DDR2 transfers 64 bits of data twice every clock cycle. DDR2-SDRAM memory is not compatible with current DDR-SDRAM memory slots.
See also DDR-SDRAM.