Double Data Rate (DDR) SDRAM memory is a product built upon the foundation of older PC100/PC133 memory technology. DDR SDRAM memory can do two operations per clock cycle, unlike SDRAM memory which only supports one operation per the computer's clock cycle. By having DDR technology, you are doubling the memory bandwidth over the corresponding single-data-rate SDRAM.
DDR is the evolution of SDRAM memory technology. Double Data Rate (DDR) memory features higher data bandwidths, faster speeds and enhanced thermal performance.