This is a follow on to the article What’s Peer to Peer?

BitTorrent is a popular P2P sharing system. It’s great strength is that it is free and open source. So everyone can see how it works.

To download a file using BitTorrent, you first need the program and then the Torrent which is a small file that tells your machine where it can find the file. The Torrent points to the seeds. As you join the download swarm for that particular file, your machine will find out who else is downloading the same file and you all share the load.

What happens is the original file is “seeded” (uploaded) to a number of computers (nodes). Then as people start to download that file, they get bits of the file from the seeds and bits of it from each other, sharing the download. So your machine is uploading bits of the file that you already have to other people who haven’t got that bit yet at the same time as you get bits you need from other people.

The more popular a file, the more downloaders, the better BitTorrent works. With more nodes, it goes faster. It is also rewarding of people who upload, giving them better download speeds, allegedly. Unlike a traditional web server which slows down with the more load you put on it, BitTorrent speeds up with greater load.

Popular BitTorrent programs include Azurus and utorrent.

Finding the torrent file for what you want can be tricky. There are some notorious sites like Pirate Bay that blatantly list torrents for just about everything. See the other article for my thoughts on legal issues.