Source : Free On-Line Dictionary of Computing

TOS
     
         /toss/
     
        1. {IBM}'s {Tape Operating System}.
     
        2. The {operating system} of the {Atari} ST range of
        computers.  This range included the 512ST, 1040ST and the F,
        FM and E variations (e.g.1040STE).  Later, 32-bit machines
        (TT, Falcon030 and MegaSTE) were developed using a new version
        of TOS, called {MultiTOS} which was based on {MinT}.
     
        TOS went through several revisions starting initially as a
        derivative of {CP/M}, but developing into a remarkably
        complete and flexible operating system.  Features include: a
        {flat memory model}, {MS-DOS}-compatible disk format and
        support for {MIDI} and {SCSI} (in later versions).  TOS was
        designed to run Atari's version of the {GEM} {GUI}.
     
        There is some argument as to what TOS stands for, the main
        candidates being "Tramiel Operating System" (named after
        Atari's head at the time) or simply "The Operating System".
     
        3.  {Terms Of Service}.
     
        4. Star Trek The Original Series as opposed to ST-TNG or
        ST-DS9.
     
        (1999-04-02)