An early example of a DRM system was the Content Scrambling System (CSS) employed by the DVD Forum on film DVDs since circa 1996. CSS used a simple encryption algorithm, and required device manufacturers to sign license agreements that restricted the inclusion of features, such as digital outputs that could be used to extract high-quality digital copies of the film, in their players. Thus, the only consumer hardware capable of decoding DVD films was controlled, albeit indirectly, by the DVD Forum, restricting the use of DVD media on other systems until the release of DeCSS by Jon Lech Johansen in 1999, which allowed a CSS-encrypted DVD to play properly on a computer using Linux, for which the Alliance had not arranged a licensed version of the CSS playing software.
Microsoft‘s Windows Vista contains a DRM system called the Protected Media Path, which contains the Protected Video Path (PVP). PVP can prevent DRM-restricted content from playing while unsigned software is running in order to prevent the unsigned software from accessing the content. Additionally, PVP can encrypt information during transmission to the monitor or the graphics card, which prevents unauthorized methods of video recording.
Source : wikipedia