DDR - Double Data Rate (RAM - Random Access Memory)
Double Data Rate Synchronous Dynamic RAM, Double Data Rate SDRAM or simply DDR RAM, is a type of SDRAM that handles data more efficiently than SDRAM. Theoretically, DDR SDRAM transfers data twice the speed of SD RAM. It also consumes less power making it suitable for notebook computers.
Technically speaking, a DDR RAM supports data transfer on both edges (the rising and falling edge) of each clock cycle, effectively doubling the data rate. On the other hand, traditional SDRAM can transfer data only on the rising edge of the signal. That's why DDR SDRAM is also known as SDRAM II.