Quad Data Rate SDRAM Quad Data Rate ( QDR ) SDRAM is a type of computer memory , more specifically a type of synchronous dynamic random-access memory , that can transfer four words of data in each clock cycle . Like Double Data-Rate ( DDR ) SDRAM , QDR SDRAM transfers data on both rising and falling edges of the clock signal . Unlike DDR SDRAM , which has a single bidirectional read-write port , QDR has separate read and write ports that can operate simultaneously . This requires a larger number of wires from the memory device to the memory controller , but doubles the theoretical maximum data transfer rate . QDR SDRAM uses two clocks , one for read data and one for write data .  This computer hardware -related article is a stub . You can help Wikipedia by expanding it . Categories : Computer hardware stubs | Computer memory 