When a CPU has say 2 Maximum Memory Channels, and you install 4 physical cards of RAM. What does this actually do? Are two of them used at any one point in time? If so, are the second 2 redundant? Is it better to go with 2x higher GB RAM or 4x lower GB RAM. Which would perform better?
How Does the Maximum Memory Channels Limit the Amount of RAM
memory
Best Answer
The RAM controller has a specific capacity for driving its interface lines. Each DIMM - or rather each chip on the DIMM - puts a certain load on the memory bus, so there's a maximum of DIMMs/chips you can attach. Special types of DIMMs reduce the load: registered (RDIMMs) or load-reduced DIMMS (LRDIMMs) buffer signals between the controller and the chips and enable the bus to drive more chips in total (when this is supported by the system).
This limit is applied to each memory channel, so when a dual-channel controller can drive two DIMMs it can drive a total of four DIMMs.
The total amount of RAM is simply the maximum number of DIMMs multiplied by the size of the largest DIMM the system supports.
In practice, this is a bit more complicated - DIMMs can carry one, two or even four sets of chips (ranks), and increasing the number of ranks on the bus usually decreases memory speed. Also, not all possible numbers of ranks may be allowed in a system.
Memory channels are largely independent, so you can use all of them simultaneously to pump data to the CPU, increasing overall throughput. Often, the fastest setup is one DIMM per channel.