catflap.org Online Dictionary Query

  mode bit
       
          A flag, usually in hardware, that selects between two
          (usually quite different) modes of operation.  The
          connotations are different from flag bit in that mode bits
          are mainly written during a boot or set-up phase, are seldom
          explicitly read, and seldom change over the lifetime of an
          ordinary program.  The classic example was the
          EBCDIC-vs.-ASCII bit (#12) of the Program Status Word of the
          IBM 360.  Another was the bit on a PDP-12 that controlled
          whether it ran the PDP-8 or the LINC instruction set.
       
          [{Jargon File]
       
       

  mode bit n. [common] A flag, usually in hardware, that selects
     between two (usually quite different) modes of operation. The
     connotations are different from flag bit in that mode bits are mainly
     written during a boot or set-up phase, are seldom explicitly read, and
     seldom change over the lifetime of an ordinary program. The classic
     example was the EBCDIC-vs.-ASCII bit (#12) of the Program Status Word of
     the IBM 360.
  
  

  mode bit /mˈəʊd bˈɪt/
  Modusbit  [comp.]
   see: mode bits