BitTorrent

• BitTorrent was not the first file sharing system, but it includes innovations that makes file sharing faster and easier than with other file sharing systems. The protocol is entirely decentralized and is free to all to implement. The key elements implementing the protocol are the torrent client program and the torrent meta file. The client program is like a browser and does all the work on behalf of the user to locate and download segments of a desired file from several different sources. The client cannot do anything without the information contained in the torrent meta file.
  
  

Torrent Meta Files

• The meta file contains all the information about a particular file available for download that the torrent client needs. A torrent is a file available for copying. There may be several copies available all copied from one original file. There may be several versions of the same content available in different torrents. For example, three people have the same file on their computer, like the film, "The Incredibles." Each creates a torrent meta file and registers it with a torrent search engine. This means there are three torrents for the film available. Seven people copy one of the torrent, three people copy another and ten copy the third. There are still only three torrents floating around, though with many different copies. Those copiers who choose to leave the torrent active in their client become new sources for the file. These are called seeds. So of the three torrents, one has eight seeds, one has four and the other has eleven. These are not 23 copies of the same file, because there are three different meta files involved in sharing that film.
  
  

Content

• The meta file is a short, formatted description of the file available for download. It contains the file's name, a description and the number of blocks that file is divided into. The final element is the address of a tracker. A BitTorrent tracker is a list of IP addresses where partial or complete copies of that file can be found. The interaction between the PC, the tracker and the sources for the file is all handled by the torrent client. All the client needs is the few lines of information contained in the meta file.
  
  

Availability

• The simplicity of the meta file illustrates the ingenuity of the BitTorrent protocol. The meta file is like a tendon. It is a small element of a larger body connecting powerful muscles (the client) to a structure (the BitTorrent community). Without the meta file, no torrents can be downloaded and so there is a large collection of websites dedicated to distributing torrent meta files. The usual format of a meta file distribution web site is that of a search engine. Some are free to use, others charge a subscription fee. None hold the actual file, just the meta file.