Single-Channel
The system will enter single-channel mode when only one channel of memory is routed on the motherboard, or if two-channels of memory are routed, but only one channel is populated. In this configuration, all memory cycles are directed to a single channel.
Dual-Channel Asymmetric
This mode is entered when both memory channels are routed and populated with different amounts (MB) of total memory. This configuration allows addresses to be accessed in series across the channels starting in channel A until the end of its highest rank, then continue from the bottom of channel B to the top of the rank. Real world applications are unlikely to make requests that alternate between addresses that sit on opposite channels with this memory organization, so in most cases, bandwidth will be limited to that of a single channel.
Dual-Channel Symmetric
This mode allows the end user to achieve maximum performance on real applications by utilizing the full 64-bit dual-channel memory interface in parallel across the channels with the aid of Intel® Flex Memory Technology. The key advantage this technology brings is that the end user is only required to populate both channels with the same amount (MB) of total memory to achieve this mode. The DRAM component technology, device width, device ranks, and page size may vary from one channel to another.