dual boot
multiboot
multiple boot

    Any system offering the user the choice of
   two operation systems (OSes) under which to start a
   computer.  A dual boot system allows the user to run programs
   for both operating systems on a single computer (though not
   simultaneously).  The term "multiple boot" or "multiboot"
   extends the idea to more than two OSes.

   The OSes are generally unaware of each other's existence.
   They are installed on separate hard disk partitions or on
   separate disks.  They may be able to access each other's
   files, possibly via some extra driver software if they use
   different file systems.

   The OSes need not be completely different - they might be
   different versions of Microsoft Windows (e.g. Windows XP
   and Windows NT) or Linux (e.g. Debian and Fedora).

   A dual boot system differs from an emulator such as
   vmware, which runs one or more OSes "on top" of the primary
   OS, using its resources.

   (2005-02-01)