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 minicomputers and mainframes whereas the
   cheaper parity protection is more common in microcomputers.

   [Clearpoint, "The Designer's Guide to Add-In Memory", Third
   Addition].

   (1995-10-10)