DuckCorp Dico

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1.                 From The Free On-line Dictionary of Computing (19 January 2023):
                   
   
   
                   
                     
   OS
      1. operating system.
      2. [obsolete, ITS], an output spy.  See "OS and JEDGAR".
      3. <operating system> An operating system from IBM for
      their System/360 line of hardware announced in 1964.  OS was
      planned with several flavours that were supposed to be
      compatible.  OS was late, memory hungry and not able to reach
      the marketing objectives of IBM for the 360/30, the planned
      successor of the IBM 1401.  IBM then decided to design a new
      operating system for the low end machines which they called
      DOS/360.
      [Jargon File]
      (1997-09-22)