What is meant by Registered memory?
"Registered" is a means of "Buffering" the memory in SDRAM. This means that the clock signal is boosted across the entire array of memory chips so that the computer sees a clean sharp clock signal instead of a weakening clock signal as it progresses along the length of the memory path. Registered memory must be supported by the system board and cannot be mixed with "Unbuffered" modules.
You must have only Registered memory to use Registered memory. This is a further means of eliminating the possibility of errors when reading the data in memory and is used when the data returned from memory is extremely critical, such as in scientific or financial calculations where the integrity of the data is CRITICAL. It also allows a module to be built using more chips, allowing for larger capacity modules to be made.