Registered memory

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Not to be confused with ECC memory, although memory modules often use both technologies.

Registered (also called buffered) memory modules have a register between the SDRAM modules and the system's memory controller. They place less electrical load on the memory controller and allow single systems to remain stable with more memory modules than they would have otherwise. Registered memory is more expensive because of the additional components, so it is usually found only in applications where the need for scalability and stability outweighs the need for a low price (servers, for example). Although most server-grade memory modules are both ECC and registered, there are both, registered non-ECC modules and non-registered ECC modules.

There is a performance penalty for using registered memory. Each read or write is buffered for one cycle between the memory bus and the DRAM, so the registered RAM can be thought of as running one clock cycle "behind" an equivalent unregistered DRAM.