Which of the following technologies when implemented allows for the GREATEST fault tolerance for memory?

RAID (Redundant Array of Independent Disks) provides fault tolerance by combining multiple physical disk drives into a single logical unit, distributing data across them with redundancy. This setup allows data to remain accessible even if one or more individual drives fail, offering a high level of fault tolerance for the system's persistent data 'memory' or storage subsystem.

Registered memory adds a buffer to stabilize electrical signals for better reliability in systems with many DIMMs, but it does not provide fault tolerance against memory errors or module failures.

ECC (Error-Correcting Code) memory can detect and correct single-bit memory errors and detect multi-bit errors, improving data integrity, but it does not provide the broad fault tolerance against physical module failure or redundancy at the scale RAID offers for data storage.

Memory pairing is not a standard, widely recognized technology for achieving the greatest fault tolerance; while some systems implement memory mirroring for redundancy, 'memory pairing' itself is too vague and typically refers to channel configuration for performance rather than fault tolerance.