What is Bit Torrent?

Posted By BrokenClaw on April 2, 2008

BitTorrent is a specialized method of a larger process called peer-to-peer file sharing. Peer-to-peer (often abbreviated and pronounced P2P) is the term used to describe a method of file transfer that goes from one user (a peer) to another user (a peer), without using a computer server in the middle. A typical home network, where several computers are connected via a router, can be a peer-to-peer network if the computers are set up to share files among each other. The real value, though, is when the entire Internet is used as the network, and the peers can be anywhere in the world. Computers on a P2P network are called nodes.

The normal procedure for transferring files on the Internet is for users to upload and download files from a server, such as a website. However, with large files and large amounts of data, such transfers can create strains on the bandwidth limits at either end. Peer-to-peer takes advantage of the distributed bandwidth of all the users. In other words, the file gets transferred from someone who already has the file, instead of everyone trying to get the file from the same place.

It is similar to a phone chain that organizations often set up to disseminate news quickly. Instead of having one person call everyone else, the first person calls a few people, and each of them are assigned to call a few more people, and so on. Since P2P usually involves file transfers in both directions, it is called file-sharing. The P2P process requires special software to be installed on each of the participating computers.

The next step in making peer-to-peer file sharing more efficient is the addition of torrent technology, commonly described as the BitTorrent protocol. Instead of transferring complete files, the files are broken into small chunks which are shared individually across the P2P network. When a user wants to download a large file, the software, called a BitTorrent client, finds nodes on the network that have the file and begins to download small chunks from all over.

BitTorrent® is actually the proprietary name of a particular software program. But like many innovations (Kleenex®, Jello®, Xerox®, etc.), the original brand name often becomes synonymous with the generic product.

It would be as if you wanted to read a book, but instead of getting the whole book, you get a copy of a few pages of the book from everyone who already has it. And then once you have the book, you become a participant by sharing copies of your pages. There are dozens of BitTorrent clients available online, each with their own features.

Obviously, the software has to keep track of which chunks you’ve gotten and has to reassemble them in order. The more nodes there are with the intended file, the more efficient the process.

The initial distribution of a file onto the network is called seeding. Once the file is seeded, it can be shared among the nodes, creating more seeds, and so on. The speed at which a file is finally transferred depends on the size of the file, the number of seeds available, the number of clients trying to access it, and the transfer speed at either end of the connection.

Peer-to-Peer file sharing and the BitTorrent protocol are important tools for reducing bandwidth usage with large file transfers. Like many other technologies, they can also be used for illegal purposes, including the practice of sharing copyrighted material such as music, movies, and software. In fact, that’s probably where they get the most usage. As a result, people often automatically associate P2P and BitTorrent as being illegal, which they are not. They are often cited in discussions of Net Neutrality.

An example of legal BitTorrent usage is the downloading of free and open-source software packages, which are often quite large, such as distributions of Linux. Another example, which relates to the book analogy above, is Project Gutenberg, a website which distributes free and legal digital versions of books, usually called eBooks, by direct download or by P2P.

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