A digital music library is a external hard drive containing digital files of your music. The portable hard drive serves as backup in case your computer fails, or you lose your iPod or mp3 player. The HDD can be plugged into any computer with a USB port. From there you can shuffle files to the device of choice such as iPod, mp3 player or media device. The digital music library is neatly organised alphabetically by artist, album and song and also contains album art.