Bram Cohen

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Bram Cohen is the developper and founder of Bittorrent, the disruptive technology that facilitates downloading of large (video and other) files on the internet.

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"A well-researched and fascinating profile of Bram Cohen, the writer of the most disruptive technology of the period, the BitTorrent code. The profile outlines his past, his Asperger syndrome, and why the Moving Picture Association is not after him, despite Bittorrent movie downloads costing them 4% of total revenue.

"Before BitTorrent, large file transfers basically operated like the world's slowest Blockbuster. You found someone with, say, a movie or show you wanted by going on Kazaa or searching the Net. Then you waited ... and waited ... and waited ... as bit by orderly bit assembled itself on your PC, if it ever did. Cohen's brainstorm was to break the file into pieces--typically about 1,000--and share the pain of the transfer among many downloaders. The BitTorrent software runs on a user's machine and "talks" to other users who are trying to download the same file, automatically bartering for the pieces they each need (see diagram). The more users, the faster the download. Cohen also filled the program with canny details: For example, when a file first goes up, machines can download chunks only as fast as they upload them, deterring freeloaders who want to receive but not give. The program also always tries to snag the rarest piece of the file first. The idea? The more machines that have that rare piece, the less rare it becomes.

The first real world test of whether the principles would work on any large scale came in 2003, when open-source software company Red Hat released its Red Hat Linux 9 operating system. Demand for the product was so strong that downloaders crippled Red Hat's servers. Eike Frost, a computer science student at Germany's University of Oldenburg, however, had managed to get a copy. He ran it through BitTorrent, then posted a link to popular tech site Slashdot, inviting folks to come and get it. The swarm was immediate. Within three days the Red Hatters traded 21.15 terabytes of data--equivalent to more than all the books in the Library of Congress. At the peak, nearly 4,500 computers were swapping pieces of the file at any one time, uploading and downloading at a rate of 1.4 gigabits each second. Frost estimates that if he had leased a line to handle that much traffic, it would have cost him $20,000 to $60,000. Instead he paid his usual $99 server hosting bill." (,15935,1117681,00.html)

More Information

  1. Business Week Profile at
  2. See Fortune magazine for a profile and interview at,15935,1117681,00.html