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For many people, the ultimate music format used to be the cassette tape: Cassettes were portable and easy to use, and tape players were cheap. Then along came compact discs, which were just as simple and portable as tapes, but sounded better. Now CDs are being challenged by the new wave of digital audio, which is even more portable.

For about $250 you can buy an MP3 player that holds more than 150 CDs' worth of music, has a battery that lasts about 8 hours, and is only slightly bigger than a pack of playing cards. But switching from the familiar world of cassettes and CDs to the far more complicated world of digital audio means not only selecting the right hardware but also figuring out where to find the audio files you want, how to process them, and how to manage all of your music. With a little bit of planning and getting up to speed, however, creating such an audio library should be easy.

The digital audio revolution began in 1987, when the Fraunhofer Institute in Germany began working on a technology that may one day make the CD as passe as eight-track tape: a file compression scheme that came to be called MPEG Audio Layer 3, aka MP3, capable of creating digital audio files as small as one-tenth the size of an uncompressed file. Sure, the compression results in some loss of quality, but it gave something in return: portability and versatility. As the MP3 format grew in popularity, users found that they could store thousands of easily accessible tracks on their PCs. And--despite Napster's ongoing legal troubles--MP3 music is here to stay.

These days, tiny portable devices allow you to take compressed music with you. Newer compression formats like windows media audio and realaudio shrink files to ever-smaller sizes. Sophisticated applications can convert audio to those and other formats, and then play it. Countless Web sites offer music in a wide assortment of genres. To help you pick which components you need to bring the music home (and take it on the go), we've assembled a guide to each, beginning with where to find tunes.