http://www.pcmag.com/encyclopedia_te...i=54537,00.asp
Basically-- the Registry contains ALL of your computers configuration in one place...
It tells the system what hardware should be running (in Windows)
what motherboard you have/how much
ram is installed/what type of harddrive/how many
what software should run at system startup/what order it should startup in
how the desktop should be displayed-- down to the icons for program shortcuts/where they are located etc.
Every detail of what makes your system work/how you've customized it/what software you have installed is stored here.
That's why every computer tech I've ever seen says backup,backup,& backup again. If you have a backup copy of your systems' settings you can literally have your sytem back up and running in an hour less if you're experienced at what needs to be saved (not everything does)-- If you do this ... and you have to reinstall Windows you can literally have your system back EXACTLY how you left it. Right down to those special picture files/important emails/system tweaks... everything.
Editing the registry can also save you from having to reinstall-- or fix that annoying problem-- but it is not for the inexperienced-- & should not be attempted without careful instruction/guidance for the 1st few times