RDIMM vs UDIMM
RDIMM adds a register chip that buffers command and address signals for higher capacity. UDIMM skips that chip for lower cost and latency.
RDIMM, or registered DIMM, places a register chip between the memory controller and the DRAM on the module. That chip, usually called an RCD, buffers the command and address signals but not the data itself. Lowering the electrical load on the controller lets each channel carry more ranks and more capacity. UDIMM, or unbuffered DIMM, skips the chip, so address and command lines run straight from controller to DRAM. That keeps cost and latency down, but the controller can drive fewer ranks before signal integrity suffers.
The register costs about one clock cycle of latency, small but real on latency-sensitive work. RDIMM is almost always ECC and reaches high per-module capacities. Servers and workstations with eight or more memory channels per socket use it to build multi-terabyte configurations. UDIMM, ECC or not, dominates desktops and entry workstations, typically two channels with one or two DIMMs each.
Check the board manual before ordering memory. It will name one type or the other, and the wrong one simply will not boot, because boards are wired for a single type.
Sources
Source | Publisher |
|---|---|
DDR5 Registered Dual Inline Memory Module (RDIMM) Common Standard (JESD305B.01) | JEDEC |
DDR5 Unbuffered Dual Inline Memory Module (UDIMM) Common Standard (JESD308B) | JEDEC |
Last verified August 29, 2026.
- registered DIMM
- unbuffered DIMM
- ECC memory
- LRDIMM
- memory channels
- server memory
- DIMM ranks
- RCD chip
- workstation memory