That refers to the operation mode of the memory. \n\nThere are two modes, single-channel and dual-channel.\n\nWhat this means is how the computer access the memory to retreive information, if the Main Board only has single-channel operation, then the data of the memory only can be accessed sequentialy no matter how many memory chips you have.\n\nWhen the operation is double-channel, then the memory slots on the main board has two different colors, one for channel A and one for channel B. This allows the computer to access two differents memory locations at one time, of course, if you have at least one chip on channel A and one chip en channel B.\n\nFor more information see the reference: