In dual-channel motherboards you have two independent memory controllers. As long as you have RAM inserted in slots controlled by each then you are running in dual-channel mode. For example if controller 1 is attached to slots 1 and 2 and controller 2 is attached to slots 3 and 4 then at a minimum if RAM is placed in slots 1 and 3 or slots 2 and 4 then you are running in dual-channel mode. If you place RAM in slots 1 and 2 or 3 and 4 you are not. Motherboards with only one memory controller will always be single-channel no matter how may sticks of RAM you have. In theory with dual-channel if you could access both the channels continuously and half the accesses were on each channel then you might come to doubling the memory bandwidth using dual-channel. This is rarely obtained so at most you might 5%-10% increase in benchmark performance. In practice you might not see any diference. Processors with hyperthreading have two pipelines. However only one has access to the cache or system RAM at a time. They both can run at the same time as long as they do not need access to cache or RAM. If one pipeline is using cache or RAM and the other needs it then it must wait for the other to release it. That is why hyperthreading only gives maybe 10%-20% increase in performance over a single processor. In dual-core processors you have two independent processors each with its own cache. Then there are either one or two memory controllers not necessarily dedicated to a particular processor. They can both run at full speed as long as the executing code are contained within the cache. If RAM access is neeeded then only one can execute at a time unless you can dedicate a memory controller to each and RAM to each. Motherboards with two or more processors can be set up to have memory dedicated to each processor as well as shared memory. I do not know if that will be done with dual-core since that will require more total system RAM. Intel has the memory controllers on the motherboard while AMD's Athlon 64s have the memory controllers on the die with the CPU. AMD designed the Athlon 64 with on die memory controllers and multiple cores in mind. Implementing dual-core processors was a logical step for them. On the other hand Intel's attempt at dual-cores was a desperate attempt not being left behind. They simply slapped two P4 cores together and called it dual-core. Benchmarks for dual-core processors clearly show that the AMD ones leaves the Inel ones in the dust. The same is true for the server/workstation market where dual-cores give the most benefit. AMD dual-core Opterons are not only much faster but they run signicantly cooler and use a lot less power than their Xeon counterparts. Xeons with two dual-core processors running hyperthreading were showing 8 logical processors could not beat Opterons with two dual-core processors that only had 4 logical processors.

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