DDR SRAMs GSI Technology SigmaDDR™ SRAMs are synchronous memories with a common read and write data bus that combines capacity and performance with transaction rates unequaled by competitors. SigmaDDR SRAMs 'DDR' refers to the ability to transfer two beats of data on the data bus in a single clock cycle. SigmaDDR memories are ideal for applications that alternate between read and write operations infrequently, at operating speeds of 250 MHz and above. GSI's SigmaDDR devices are compatible with all competitor Double Data Rate SRAMs.