I just read that DLP (digital movies in theaters) is regaining momentum. Today is 2007 July and indeed several nearby theater complexes now have at least one digital projector. Business Week says that digital movies are now delivered on 500GB(= 4Tb) hard disks by truck. The movie is copied onto a theater disk and then the truck drives on to the next theater. The copy takes about as long to copy as to perform. I suppose that the disks involved have the same read and write speeds. Mag disks are like that and reading 4Tb in 4 ks (4000 seconds) is 1 GHz which is a respectable bit rate. They speak of replacing the trucks with satellites. The purpose of this note is to ponder whether land lines can do the job.

Long haul fiber links carry about a THz but the link terminations are expensive. I imagine that moving the movie more than a few hundred miles is best done with such efficient links. (Efficient bit miles) I also imagine that you don’t want to move the same movie across the country all over again for each of the hundreds of theaters that the movie will soon open in. This suggests an internet broadcast mode but I dismiss RSVP out of hand.

I think that wherever the THz links go the movie can economically follow, once. If the movie can move in a few hours that should be good enough. This seems highly plausible as it will not unduly impact normal traffic. It can probably even be done over internet protocol as a vanilla IP customer. Perhaps latency requirements dictate that the movie get to theaters in 48 hours. If several movies are to open some Friday, then several movies—perhaps 20 Tb, must arrive at a particular theater over a local land line in 48 hours or 200ks. This requires a 100 MHz local link. This link is several DSL links, or a T3.

The solution is perhaps distributed centers which relay the movies to theaters located within perhaps 100 miles and which are connected by private T3 circuits. It is hard to find prices of short haul T3 links; the presumption now is that any T3 is a connection to Internet. I presume that some still provide unbundled end-to-end T3 circuits.

Traffic at such a center is a bit of a problem, but not as much as it might first seem. I assume disks at the center with capacity of perhaps 48 Tb (6TB) disk capacity but with a high ratio of disk bandwidth to capacity. This allows feeding the movies to theaters by making one pass over a movie-on-disk, per theater, if necessary. Unconventional error correction is available to make these total transfers highly robust.