Dual-channel architecture

From Wikipedia, the free encyclopedia

Dual-channel architecture DDR/DDR2 SDRAM describes a motherboard technology that effectively doubles data throughput from RAM to the memory controller. Dual channel-enabled memory controllers utilize two 64-bit data channels, resulting in a total bandwidth of 128-bits, to move data from RAM to the CPU.

In order to achieve this, the DDR/DDR2 SDRAM memory modules must be installed into matching banks, which are usually color coded on the motherboard. It is not required that identical modules are used, but it is often recommended. One module of 512MB RAM could be installed in bank one and a 1GB module could be installed in bank two. Modules rated at different speeds can be run in dual channel, although the motherboard will then run all memory modules at the speed of the slowest module. Some motherboards however have compatibility issues with certain brands or models of modules when attempting to use them in dual channel mode. For this reason it is generally advised to use identical pairs of memory modules and most memory manufacturers now sell "kits" of matched pair DIMMs. Several motherboard manufacturers only support configurations where a "matched pair" of modules are used. Dual-channel architecture is a technology embraced by motherboard manufactures and does not apply to memory modules. In other words, any matched pair of memory modules may support single and dual-channel operation, provided the motherboard supports this architecture.

[edit] Purpose

Graphic illustrating bottleneck between CPU, RAM, and other peripherals

Dual channel technology was created to address the issue of bottlenecks. Increased processor speed and performance requires other, less prominent components to keep pace.

The most conspicuous of these parts is the memory controller, which regulates data flow between CPU and the system memory (RAM). 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 bottle-neck 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 bottleneck is reduced. Rather than wait for memory technology to improve, dual channel architecture simply takes the existing RAM technology and improves the method in which it is handled. While the actual implementation differs between Intel and AMD motherboards, the basic theory stands.