Memory rank: single / dual / quad rank
A memory rank is a 64-bit (72-bit with ECC) block of DRAM chips accessed together by the memory controller. A DIMM can have one, two, or four ranks. Rank count affects capacity, performance through interleaving, and how many DIMMs a channel can support.
The controller reads and writes one rank at a time, but it can interleave across multiple ranks to hide latency and keep the bus busy, so dual-rank DIMMs often outperform single-rank at the same capacity. More ranks per DIMM also raise electrical load on the channel, which is why platforms cap the total ranks a channel can drive.
A single-rank DIMM has one rank, dual-rank has two, and quad-rank has four. Rank count combines with chip density to set module capacity. Every platform specifies a maximum ranks-per-channel limit, and exceeding it forces the memory to run slower or prevents full population.
When configuring memory for servers from China, check the CPU's ranks-per-channel budget before filling every slot, especially with quad-rank or LRDIMM modules. Dual-rank RDIMMs are usually the sweet spot for performance per dollar. Keep ranks balanced across channels for even interleaving.
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