this is a technical detail about which I knew
nothing although it is logical and it might be important with beginners that use
some OSes not very suitable for everyday use.
I had to reinstall Dreamlinux today because I messed up the GUI completely and
it crashed my PC for good. I reinstalled it without formatting the Linux
partition on my large SATA drive and such I preserved all the files, installed
programs and settings, even the wallpaper on my PC. Here is a video about this:
http://www.youtube.com/watch?v=eB2WfHES3cw

I will redo this under Ubuntu on my IDE drive by choosing the option custom
partitioning (or manual partitioning, whatever, the last one at the bottom) and
not check the format option for formatting the partition, so as to see what
happens.