The really good news is that you’ve already backed up the part that most people miss: the licenses. The rest … well the rest is pretty easy.
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Now, if you’ve actually transferred all your music files from CDs to begin with, you are, effectively, already backed up. But as you point out, that’s hours of painstaking transferring (or “ripping”, as it’s more commonly known as). By backing up the .wma files (or .mp3 files or other compressed music files), restoring them later is significantly faster … it’s a simply copy operation back into the “My Music” folder, or wherever you had them. And the .wma files are compressed, so what might have been 6 or 8 CDs on your bookshelf may well fit on a single backup CD.
This might also be a situation where it’s pretty nice to have a DVD burner of some sort. Like you I’ve ripped most of the CDs on my bookshelf onto my PC so that they’re quick and easy to listen to as I live my life at my computer. In addition, I’ve also purchased a fair amount of music using Apple’s iTunes so in among my MP3 files that I could restore from my original CDs are a number of Apple’s M4P files that I have nowhere else. In my case, that’s 16 gigabytes of music right now. It’d be much better to back that up to, say, 4 DVDs than it would to try and manage the roughly 25 CDs it would require for backup. (And I really should get around to backing it up.)
One final note: naturally I recommend backing up more than just your music. I’m sure there are lots of things on your computer that, if lost, would also be painful, if not impossible, to restore. As I’ve discussed in a prior article, “What backup program should I use?“, the simplest solutions are backup packages that simply backup your entire hard disk. That would, then, include your music, your work, your email and whatever else you had on your machine.
But one way or another, do back up. Someday you’ll thank me.