Monday, December 13, 2010

Beginners' Guide to BitTorrent

Torrents are really interesting. I am not a pirate, I would like to mention, as people usually link torrents to illegal movie and music sharing. But there's a lot more to torrents. It's a way to share files peer-to-peer, and not just pirated stuff.

Note: Let me blow out all the misconceptions. Torrenting is not illegal. Just sharing pirated stuff is illegal. You won't be caught uploading your home video to your family at all.

Torrents (or BitTorrents, explained later) was created by programmer Bram Cohen's company in 2001. The protocol (other examples are http for websites, ftp for file transfers, irc for some old fashioned chat, pop3 and imap for email) is now maintained by his company, called BitTorrent Inc. Yes, really. And BitTorrent is the official torrent downloading program, though maybe not the best for many people.

How it works, and terminology
In this sections, I will explain how torrents work, and the key terms for this system will be marked out in bold lettering.

In a nutshell, BitTorrents (or just torrents) are a protocol that devices use to connect together to form a swarm and share a large file to each other, uploading and downloading simultaneously.
When a file has to be distributed over torrents, the person who has it first makes it available on a server, or his own PC (could be anything that can run torrent software). This location is called the seed. A seed is a location which has the complete file, and that uploads it to others. Then, he distributes a small file with a .torrent extension via the web (probably as a download) or even email. This little .torrent file can be opened using a torrent client (BitTorrent, Transmission). What it does is that it directs the client software towards the seed.

The people running the client software (that download the file from the seeder) are known as leechers or peers. There is a slight difference in the terms here. Normally, all but the seeder are initially peers. They download the file, and simultaneously upload the downloaded bits to other peers. Leecher is just a peer that does not upload the file to others. That's a selfish person.
Image from Wikipedia user Wikiadd
That image up there explains how a typical torrent swarm works. It starts from the seeder down there, and slowly and steadily, everyone's virally uploading and downloading the file.

After a file has been downloaded by a peer in the swarm, the peer turns into a seeder and remains so until he stops upload. Since he has the entire file downloaded, just like the first seeder, there is no difference. He can help seed the files to others for as long as he likes to do it.

There is also a tracker in the swarm. He maintains the record of all the people who already have the full file, partial file or whatever. He also tracks down the peers who are leechers. When a peer runs the .torrent file, he is connected to the tracker who tells the peer's client software who has the files downloaded and are seeding.

See also: My article on using Quality of Service on your network so that everyone, and all programs get the bandwidth they need. Thus, you can supercharge torrent downloads without slowing others down.

Torrent software
A torrent software, as mentioned before is a program that you can install (they're usually free) and start downloading torrents immediately. You just find a website that is giving away torrents, and download the .torrent file, run it in the client, and you already start downloading before you know it.

From Carmen Carmack's article on BitTorrent at
Here is a list of the most popular torrent clients. All of them are completely free.

  • BitTorrent - From the official creators and  supporters of the torrent protocol
  • ĀµTorrent - This is the most popular client in the world. It is an extremely small download
  • Vuze - A powerful torrent downloader with some high ratings on the web
  • BitLord - A client with built-in search, scheduler, RSS downloader and even a comments system
  • BitComet - An easy-to-use client, with a few features others do not have, though they won't be as useful to everyone

So that was all about how torrents work. Remember, play safe and do not use torrents to download pirated movies, software which stupid people distribute on the web. You can get Linux distributions like Ubuntu on torrents for free. Or you can check out sites like Jamendo where artists give away only free music. Torrents are available there.

Torrents are really fun to use. Stay tuned to my blog for some more geeky fun. You can subscribe, if you wish.