When there is a need to store a large number of photos, avatars and video files, they can be stored in a separate server called a media server. Maintaining these files on a separate server gives the advantage of allowing the main web server to handle all the videos and the media server serve up all the content. Essentially you are delegating a server to handle a particular task, thus speeding up your site. If you don't have a multi-server setup then all files and processes can be handled on a single server
