How do you copy CDs and DVDs to your hard drive as back-ups?

DVD's I'm not sure but I copy my CD's to my hard drive using Windows Media Player or any other software that converts a song from CD format to MP3 or WMA formats. A MP3 or WMA file is about a tenth the size of the original. I have over 4 thousand songs on my hard drive and it only takes up about 15 GB of space. I don't think you can back up DVD's without special pirating software.