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