A fault-tolerant memory system or "FTMS" is intended for use as mass data storage for a host computer system. The FTMS incorporates a dedicated microprocessor-controlled computer system which serializes blocks of user data as they are received from the host system, deserializes those blocks when they are returned to the host system, implements an error correction code system for the user data blocks, scrubs the data stored in the user memory, remaps data block storage locations within the user memory as initial storage locations therein acquire too may hard errors for error correction to be effected with the stored error correction data, and performs host computer interface operations. Data in the FTMS is not bit-addressable. Instead, serialization of the user data permits bytes to be stored sequentially within the user memory much as they would be stored on a hard disk, with bytes being aligned in the predominant direction of serial bit failure within the off-spec DRAM devices. Such a data storage method facilitates error correction capability.