DRM stands for Digital Rights Management, or as some people call it, Digital Restrictions Management. Put simply, DRM consists of various restrictions applied in music or video files, so their use (such as playback) can be controlled by a third party, usually the company holding the copyright for a song or movie. DRM is not just a copyright protection technique but a whole set of technologies that aim to implement the DRM strategy each distributor of digital content specifies. As an example, DRM can verify that the user that bought an audio file is actually the same user playing the file. DRM technology can also be used to limit the number of PCs a file can be played on. The major disadvantage of DRM is that these restrictions are not always clear when a user buys a digital product.

Which Multimedia Formats Support DRM?

If you're expecting to see MP3 in this list, guess again. Due to it's open nature, the MP3 standard is unable to support DRM. Furthermore, there is no centralized coordination in the development and evolution of the MP3 format so don't expect digital music stores to offer songs in the MP3 format.

Advanced Audio Coding: The AAC format, used by iTunes and iPod, is based on Apple's QuickTime. It was originally designed as a replacement of the MP3, and can actually compress files better than the MP3 format can.

Windows Media Audio: WMA is a closed-source standard of digital music. It was designed to compete with the MP3 but in reality, it's actually AAC's main competitor, especially with regards to DRM support and buying music online. The latest version of WMA offers similar quality to that of AAC and better than that of MP3 files. This means that much smaller files can have CD quality. WMA is based on the ADvanced System Format (ASF) which can integrate different streams of audio and video as long as they belong to the Windows Media family.

RealNetworks & Sony: Both of these companies offer music download services. Real mostly uses the AAC format with the Helix DRM system, while Sony uses the OpenMG DRM system on ATRAC3 files. It is expected that Sony will support other music formats in the future.

Limitations of iTunes and iPod

Finally, here are certain things that you should know about iTunes DRM:

1. Music you buy from iTunes can only be played on an iPod.

2. Files from iTunes can be played on an unlimited number of iPods.

3. iTunes allows you to download each song you buy only once and of course, you're not allowed to re-sell that song.

4. An iPod can also store and play non-DRM music files.

5. Any certified .m4p files can only be copied/played on 5 authorized computers.

6. Music you buy from iTunes can be copied to a CD without any DRM limitations.

7. A playlist consisting of songs you bought from iTunes can only be turned into a CD 7 times (you can make 7 CD copies of the list).

8. You are not allowed to convert a song to a different music format.