Before you start, make sure to back up every file that is now on
your system. The installation procedure can wipe out all of the data
on a hard disk! The programs used in installation are quite reliable
and most have seen years of use; still, a false move can cost you.
Even after backing up, be careful and think about your answers and
actions. Two minutes of thinking can save hours of unnecessary work.
Debian makes it possible to have both Debian GNU/Linux and another
operating system installed on the same system. If you plan to use
this option, make sure that you have on hand the original CD-ROM or
floppies of the other installed operating systems. If you
repartition your boot drive, you may find that you have to reinstall
your existing operating system’s boot loader[4] or the entire
operating system itself.
[4] A boot loader is responsible starting an operating system’s boot
procedure.