Here's the quick guide:
Have a smaller partition for the operating system (Windows etc), and a large one for data (music etc.)
Using this system, if your OS goes belly up, you can reinstall the OS and still have access to all your data on the larger partition when done. Watch out for the existing partitions though - you must keep them intact!

Usually, if Windows goes crazy and screws itself up, it will only affect it's own partition - not the data one. When doing a fresh install, it will set itself up and recognise the other partitions, and let you access them once it's installed.
Nothing beats having your important stuff backed up onto an external drive though - just in case!
It's the case with all precious stuff - music, photos, documents - never trust it to one place, always back it up to somewhere else - either an external drive, or to disks...
Believe me, I've been caught out too many times not to do this!
Be aware that most new computers have a 'restore partition' that MUST be left alone! This is a safety feature that lets you recover the whole computer in case of a failure. Delete that, and you'll most probably end up with a computer that is only good for for a door-stop!
(I've been there, done that too many times!

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JUST BACKUP YOUR MUSIC!! PLEASE!!!!
