atomic

   [from Gk. atomos, indivisible]

   1.  Indivisible;  cannot be split up. For example, an instruction may
   be  said  to do several things `atomically', i.e., all the things are
   done  immediately,  and  there  is no chance of the instruction being
   half-completed  or of another being interspersed. Used esp. to convey
   that  an  operation cannot be screwed up by interrupts. "This routine
   locks the file and increments the file's semaphore atomically."

   2.  [primarily  techspeak] Guaranteed to complete successfully or not
   at  all, usu. refers to database transactions. If an error prevents a
   partially-performed  transaction  from  proceeding  to completion, it
   must  be  "backed  out",  as  the  database  must  not  be left in an
   inconsistent state.

   Computer  usage,  in  either  of  the  above  senses, has none of the
   connotations  that  `atomic'  has  in  mainstream  English  (i.e.  of
   particles of matter, nuclear explosions etc.).

[glossary]