Most "Upgrade" discs will do a full install, because in certain cases a "full install"
Certain "upgrades" are blocked.
x86 (32-Bit) to X64 (64-bit) for obvious reasons.
If you are upgrading an XP system.
If you are starting with Vista Business and attempting to
upgrade to Windows7 Home... etc...
And sometimes your old installation is so completely screwed
up that anything other than a full "clean" install won't work right.
an Upgrade installation can be launched from within your old
operating system by inserting the disc and launching the installer.
on a "full" install you must boot from the disc.
Personally I prefer running an installer on a freshly formatted Hard Drive
Preferably formatted with the installation disc.
But I also like to separate the old hard drive from the process just in case
there is data you decide you need... I usually wait at least six months
before formatting a personal drive, customer drives I wait as long as
nine months to a year.
I am also adept at data recovery, particularly when dealing with pictures,
audio and video data.