How do back up programs work?

Do they just put the files into another partition or do they edxtemly compress?

Or am i way off?

I am very interested

 

I use Norton Ghost 2003 which I use to create backup images to a partition,backup to dvd and clone to a slave drive.
My XP pro operating system on C (thinned out) is 1.3 gig and ghost images created are under 800 meg.

 

is there different ways or is that the only way?

 

There are many backup utilities.I've only ever used Ghost imaging so can't really comment on others.

 

Thanx for your help it clears it a part of it up for me.