You cant back up the installed software...
i think you know that.. u r one of the senior member of this forum....
Who says U can't Back Up installed software.
let me tell u, first I didn't like the way u replied to original author of the post.
It was really arrogant and irresponsible on ur part.
answers to all questions are available on Internet, so why do so many people still ask the same questions here, because a forum is meant for it.
and remember, even u were a newcomer too this world someday. may be now u r smartest arrogant geek in town.
Back to the point,
the biggest and most important software we know is Operating System (if u knw it),
and u will find so many ppl who back up their full OS on DvDs (including me).
Apart from this there are many softwares which can still be backed up after installation. Many can not be, as we do not exactly know all the locations where they store their assemblies, if u knw , u can even store them somewhere.
Finally let me give u few examples.
a game called Quake 3 can be simply backed up by copying all the files from its installation directory, and later u can simply copy back the folder and start the game from there.Same holds true for EA cricket.
There are many more such applications which our wise friends here can bring to ur notice.