In the earlier versions of Windows 7, to play some media files, one had to download and install codec files or use alternative media player such as QuickTime, VLC, etc.
But in Windows 7, you will be able to be able to play DivX, XviD & QuickTime .mov files without installing any codecs or using alternate media players.
Microsoft has added built-in native DivX and XviD support to playback movies & video files encoded in these formats.
Simply double click the media files to play them.
