What is Digital Rights Management (DRM)?

When you download a song from a commercial online music store or subscription service, you're agreeing to use that music under the terms offered by that site. You may, for example, be limited in how you can play back that song, or you may only be able to play it on the same computer to which it was downloaded. You may also be limited into whether or how you can burn that song to CD or copy it to a portable music player. That's why it's important to read the site's terms of service before you pay.

Enforcing these playback limitations is accomplished via the use of digital rights management (DRM) technology. DRM encodes each song in a "wrapper" file, which is a type of file that tracks how the enclosed music is used. Music encoded with DRM may only be playable on computers and portable music players compatible with that particular DRM system. Trying to play a song on a non-compatible device or using the song in a manner not prescribed by the terms of service, causes the song to be unplayable.

DRM is how online subscription services track the use of their subscribers' music. All downloaded music is playable as long as the user's subscription is in effect. Once the subscription expires, the DRM wrapper flags the downloaded music as unplayable.

For most users, DRM is totally transparent. It only becomes an issue if you try to do something with the music you've purchased or rented that is not allowed in the original terms of service. And, it's important to note, most commercial CDs do not incorporate any type of DRM encoding, so you're free to copy the CDs you purchase to any number of computers or portable music players.

Michael Miller is a writer and commentator on technology and digital lifestyle topics.