On the Blu-ray disc
The director's cut is a mere three minutes longer than the theatrical cut. Many of these additions are just a few seconds of extra violence (e.g., a knife thrust into a body then pulled out), but there are a few more-substantial sequences: A longer conversation in Resistance Command Headquarters; a brief topless scene by Moon Bloodgood when her Blair Williams character and Sam Worthington's Marcus return to her base (reminiscent of Kelly McGillis and Harrison Ford in Witness); an extended conversation between those two characters afterward (Blair: "You can focus on what you've lost or you can fight for what's left"); and a longer radio address by John Connor in which he mentions his mother. Even though it's not all that different, it should be the preferred way to watch the movie.
The big extra feature, Maximum Movie Mode, is only on disc 2's original theatrical cut. In front of two large TV screens, director McG introduces the movie then makes periodic appearances to discuss key concepts. Interspersed along the way are various pop-ups with the Terminator mythology timeline, picture-in-picture with cast and crew interviews and behind-the-scenes footage, and stills galleries. You can also, when prompted, exit out of the movie to watch any of 11 Focus Points, which are two- to three-minute featurettes. Conveniently, you can also access these from the main menu. Two other features are watchable separate from Maximum Movie Mode: "Reforging the Future" (19 minutes), discussing the new film's take on the Terminator legacy, and "The Moto-Terminator" (8:33), focusing on the motorcycle-like robots. --David Horiuchi