Source : Free On-Line Dictionary of Computing

QDOS
     
         The Sinclair {QL}'s proprietary {operating
        system}.  The origin of the name is uncertain (a weak pun on
        kudos, perhaps, as {Unix} was on {Multics}).  There was
        another OS around from the birth of personal computers called
        Q.D.O.S. - Quick And Dirty Operating System.  QDOS might also
        stand for QL Data/Disk/Drive/Device Operating System.
     
        QDOS did the usual OS sorts of things, as well as
        multitasking.  It was unusual in several ways.  It treated all
        devices (serial ports, mouse ports, screen, {microdrive},
        {disk drive}, keyboard, etc.) uniformly, so you could print a
        text file direct to disk or save a binary to the screen for
        example.
     
        Also logical channels could be assigned to particular physical
        devices.  Output directed to a channel would go to the
        appropriate in/output.  This also meant you could have many
        windows on screen (the QL booted up from internal ROMs with 3
        windows - command line, output and program listing) all
        independent to some extent.  Channels could be redirected
        without affecting the way the process sent or received the
        data.
     
        (1996-07-22)