What is ECC memory?

Registered (sometimes called "buffered") memory modules have additional components 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 slightly slower than unregistered/unbuffered memory, and more expensive as well, so it is usually found only in applications where the need for scalability and stability outweighs the need for speed and a low price (servers, for example). Although many server-grade memory modules are both ECC and registered, there are registered non-ECC modules and non-registered ECC modules.