RDIMM memory (Registered DIMM or ECC REG) is a memory module that has a built-in register in addition to the ECC mechanism. It is used to amplify signals on the system bus between the RAM module and the memory controller.

Registered memory
The register function allows a stable operation of the system with more modules than usualthan is normally used. Form factor of RDIMM memory differs from standard memory. They are designed to operate in systems where quantity and stability of operation is a key element. In most cases, ECC and ECC REG modules can be used on the same platform, but cannot operate simultaneously.

Stable operations
RDIMM architecture is different from standard consumer-level memory module. This is closely related to their target applications where the key element is the amount of memory and its stability. Most platforms are compatible with both ECC and REG ECC memory, although these two types of memory cannot be used together.

More capacity
Computers support larger volumes of RDIMM memory than of ECC UDIMM.