I’m heavy into optimization for my job and I’m trying to better understand how to select RAM quantities. From my reading:
For the same DDR4 memory speed and DIMM type, more ranks will typically increase the loaded latency. While more ranks on the channel give the memory controller a greater capability to parallelize the processing of memory requests and reduce the size of request queues, it also requires the controller to issue more refresh commands. The benefits of greater parallelizing outweighs the penalty of the additional refresh cycles up to four ranks. The net result is a slight reduction in loaded latencies for two to four ranks on a channel. With more than four ranks on a channel there is a slight increase in loaded latency.
Subsequently, if I want to reduce load latency, I would think I want two to four ranks on my RAM. However, how do you know how many ranks something is?
For example, if I purchase 64GB LRDIMMs, how do I tell how many ranks that RAM has?