Capturing a hot market and exploiting technological promise are two different things. Take the DVD. The digital video (oh, all right, versatile) disc player is one of the fastest-selling consumer electronics introductions ever, with more than 2.5 million units shipped in the United States since March 1997. But for all their commercial fizz, DVDs have barely touched the interactive possibilities of the medium for presenting movies. Wide-screen format, alternate takes, cast filmographies, even directors' narrations are all well and good-but these bonus features have been available on 12-inch laser discs since the antediluvian '80s.

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