Im quite confused about memory speed rating , especially when it comes to graphics card , for example the Radeon 8500 is said to be 275mhz for the memory clock , it has 3.3 ns memory which is okay because it calculated or 1000 is divided by 3.3 , this surely gives 275 , but its somehow multiplied by 2 to give a 550mhz rating , because its DDR or some reason , well what im wondering is why PC RAM even though its DDR doesnt corespond to multiplication by 2 even though its DDR ,as the mhz rating directly matches the ns latency time??

Strange for me!!!!