Source : Free On-Line Dictionary of Computing

error correcting memory
     
         (ECM) {RAM} using some kind of {error detection and
        correction} (EDAC) scheme.  The two types of memory errors in
        RAM (especially {DRAM}) are "soft" errors due to
        radiation-induced bit switching, and "hard" errors due to the
        unexpected deterioration of a memory chip.  Soft errors do not
        indicate lasting damage to the memory board, but they do
        corrupt programs or data.  Hard errors demand physical
        repairs.  Single bit memory failures are the most common.  A
        hard single bit failure, such as that caused by a completely
        dead chip can be corrected by EDAC if each chip supplies only
        one bit of each word.  EDAC memory is the most common level of
        protection for {minicomputer}s and {mainframe}s whereas the
        cheaper parity protection is more common in {microcomputer}s.
     
        [Clearpoint, "The Designer's Guide to Add-In Memory", Third
        Addition].
     
        (1995-10-10)