Academy Frame
35mm, 16mm and 8mm film all have the same horizontal/ vertical dimensions in common: 1.37:1. This is why early films and television (pre-anamorphic) were all in what we now call "full screen." Full screen is called "Academy" format. The Academy ratio (1.37:1 before a soundtrack was incorporated onto the film) was the primary original aspect ratio.
Academy 1.33:1 aspect ratio (current) 1.37:1 aspect ratio (original)
Believe it or not, only 20 to 25 percent of the films are shot in the CinemaScope format. The rest are shot in Academy format and then widened by a technique called "matting," and it's done either as a hard matte or a soft matte. In a hard matte, the filmmaker attaches a special mask to the camera that blocks off the top and the bottom of the scene in front of it so that the film is only exposed to the aspect ratio the director wants. Usually that's 2.35:1. This is cheaper than using anamorphic lenses, and it is a good way for a director to completely control the cinematography of his picture. Because it only uses the middle of the available film area, it sacrifices image resolution somewhat.A soft matte involves filling the negative, so it's a 1.37:1 original, but only the middle part is played back. This is handled by the projectionist at the movie theater on playback. They have to properly mask the film to crop the top and bottom. There are two other dimensions to keep in mind: 1.78:1 and 1.85:1. The 1.78:1 aspect ratio is used by High Definition Television (HDTV). HDTV has been in development since the early 1980s but adoption in the U.S. has been painfully slow, due to the expense of the equipment and the large number of conflicting standards. 1.85:1 is a ratio frequently used in creating DVDs. A movie in its usual 2.35:1 ratio will still have black bars at the top and bottom of the screen, since HDTV sets have a smaller ratio. But a 1.85:1 movie played on an HDTV set is essentially full screen, filling every inch of the TV.
SOURCES:
http://www.widescreen.org/aspect_ratios.shtml
http://dvd.ign.com/articles/450/450552p2.html