35mm film in 3-D is run on a standard projector with a prism box in front of the lens. The image frames are split in half. One half the frame is for the left eye and the other is for the right. Each image half is directed through the prism box, passed through a polarizing filter and superimposed on the screen. The viewer wears polarized glasses that block the "wrong" image from being viewed by the "wrong" eye.
IMAX 3-D does use two strips of film. There are two projectors that are frame-for-frame synchronized, running two strips of 15/70 format film. There, you have the active "shutter" style glasses which receive a signal from the projector which tells them which eye is to be open at what time.
Digital 3-D is done with a standard digital projector that has a rotating glass polarizing disk in front of the lens. The projector simply projects the left and right frames alternately and the computer processor rotates the glass disk to the correct orientation at the right moment. That glass disk spins at something like 300 RPM!
I agree with JohnRichard. People go to theaters, whether they are movie theaters or stage plays, because they want to get away from their daily lives for two hours. This whole idea of presenting movies as technology and hyper reality is the same thing as people who spend all their time and money buying new and "better" camera technology but couldn't take a good photograph to save their own lives.
James Cameron is one of those people. I think his movie, "Titanic" would have been better if he knew how to edit. That movie did not need to be 3 hours long. Let me at it with a splicer and I could cut an hour out of that movie with no effect on the plot. Cameron spent all his time and energy putting cameras on deep sea submarines to the detriment of plot and substance.
The same thing goes for "Avatar." Cameron spent more time building his motion capture studio and computer generated 3-D graphics than he did the plot. Yet again, he created another 3-hour bore fest. That movie timed out at 162 minutes!
James Cameron needs to forget the 3-D. He needs to forget the computer graphics. He needs to forget the 48fps whiz-bang contraptions. He needs to go find a 16mm Bolex and shoot a couple of movies on black and white film with no sound and no special effects.
Movies, today, are all hype and zero substance.