The Economist writes about one of the peer-to-peer technologies:
The most active P2P system, accounting for an estimated 35% of all internet traffic according to CacheLogic, is called BitTorrent. It is an open-source software project that is free to use and enables very large files to be stored and retrieved efficiently at essentially no cost. Though it is used for pirated music, it comes into its own when distributing really large files such as movies, games and large pieces of software such as the Linux operating systemthings that would otherwise be very costly for companies or individuals to make available for download.
Part of BitTorrent’s success stems from the way it creates incentives for users to give as well as to take. A study in 2000 on one P2P network showed that almost 70% of users never shared files, and around half of the files available were offered by just 1% of users. BitTorrent is designed to remedy this. It rewards those who share files with others by increasing the download rate at which generous users can receive content, explains Bram Cohen, the system’s creator. More sharing means there are more potential locations where copies of a given file are located, which in turn increases access speed. BitTorrent uses a technique called swarming, in which files are broken into small chunks that are then passed between peers. Two peers downloading the same file at the same time can also swap chunks they have already received from other peers, increasing the efficiency of the transfer.