DRAM - What are "unbuffered" and "registered" (reg) memory modules ?

UNBUFFERED - No buffer the memory is connected directly to the chipset controller,  DDR, DDR2 and DDR3 modules that are used in desktops or notebooks are mostly unbuffered.

BUFFERED - A buffer is used to help the system control large amount of memory. Used to describe older technology modules such as EDO and SDRAM. Used in servers

REGISTERED - Registered modules do not have a buffer but do contain a register that delays all information transferred to the module by one clock cycle, this increases reliability and applies to DDR, DDR2 and DDR3 modules used in many servers.

FULLY BUFFERED - please see FAQ . Applies only to DDR2 modules used in servers