Microsoft has stunned its E3 conference audience by announcing native backwards Xbox 360 game compatibility on Xbox One. The service launches for everyone this holiday - autumn - but Xbox Preview members can test it now. It will be free and launch with support for 100 titles. Hundreds more titles will be added after that. All developers need to do is approve the game's backwards compatibility - no extra development is needed. Digital games will show up automatically in your library on Xbox One, or you can put your retail disc in and verify ownership that way. Xbox One media features will be available to use when playing the older games. Microsoft demonstrated Mass Effect 1 running in backwards compatibility. Microsoft rounded off the announcement with a quip about not charging you to play games you already own - a thinly veiled dig at Sony and its PS4 remasters of PS3 games.