Dual channel DDR SDRAM is a motherboard technology used to increase memory performance, by using two channels to load data into memory. The memory controller utilizes two 64 bit data channels, resulting in a total of 128 bits, effectively doubling the bandwidth to memory. In order to achieve this, the DDR SDRAM memory modules must be installed into matching memory slots, which are usually color coded on the motherboard. Each memory module in each slot must be identical to the one in its matching slot.
Reason For Being
Dual channel technology was created to address the issue of bottlenecks. Increased processor speed and performance requires other, less prominent components are required to keep pace. 
The most conspicuous of these parts is the memory controller, which regulates data flow between CPU and the system memory. The memory controller determines the types and speeds of RAM as well as the maximum size of each individual memory module and the overall memory capacity of the system. There are many memory controller designs; prior to 2003, the most common was the single channel configuration. Among its advantages are its low cost and flexibility. Its ability to produce a bottleneck effect arises when it is unable to keep up with the processor, leaving it with nothing to process while the memory controller is struggling to keep up with the data flow. Under the single channel architecture, any CPU with a bus speed that is greater than the memory speed would be liable to fall prey to this bottleneck effect.
The dual channel configuration alleviates the problem by doubling the amount of available memory bandwidth. Instead of a single memory channel, a second, parallel channel is added. With two channels working simultaneously, the . Rather wait for memory technology to improve, dual channel architecture simply takes the existing RAM technology improves the method in which it is handled. While the actual implementation differs between Intel and AMD motherboards, the basic theory stands.
External Links
Whitepaper on Dual Channel Memory
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