Single rank vs dual rank

A rank is the set of DRAM devices that one chip-select signal addresses. The Linux EDAC documentation says a single-ranked stick has one chip-select row, and a double-ranked stick has two, over different devices, which cannot be accessed concurrently. In AMD's and Supermicro's module tables, 1Rx8 marks a single-rank module of x8 chips and 2Rx4 a dual-rank module of x4 chips. Vendors also write SR, DR, 1R and 2R.

AMD's EPYC 9004 memory guide lists RDIMMs of 16 GB 1Rx8, 32 GB 1Rx4, 32 GB 2Rx8, 64 GB 2Rx4 and 96 GB 2Rx4. The two 32 GB entries match in capacity and differ in rank count. The guide lists 4,800 MT/s for both 1R and 2R RDIMMs with one DIMM per channel, and says an interleave set needs the same DIMM type, capacity and ranks on every channel. On Supermicro's H14SST-G with EPYC 9005 at two DIMMs per channel, the A+ brochure rates 1R RDIMMs at 4,400 MT/s and 2R at 4,000 MT/s.

Match rank count and capacity on every channel. Take 1R modules for two DIMMs per channel when the board rates 2R lower, as the H14SST-G does. At one DIMM per channel, choose on capacity.

Sources

Last verified October 30, 2026.