Unbuffered memory is memory where the memory controller module drives the memory directly, instead of using a store-and-forward system like registered memory. Buffered memory modules have built-in registers on their address and control lines. A register is a very small temporary holding area (usually 64 bits) for data. These registers act as buffers between the Glossary Link CPU and the memory.
Some systems do not support unbuffered memory, others require unbuffered memory, and many more give you the option to use unbuffered or registered memory. The use of unbuffered memory is reasonable for gaming systems. It is not recommended for server-class systems.
Kingston registered memory
The use of registered memory increases the reliability of the data, that is why most true servers motherboards require registered memory. Registered memory is slightly slower than unregistered memory (1 clock cycle) as data must be moved through the registers. The use of registered memory is recommended for server-class systems. It is not useful on gaming systems.
Finally, the unregistered RAM is cheaper than the registered RAM.