How Torrents Work
It starts off with someone who wants to share a file. The person needs to somehow announce to the world that they have this file. Well, it just so happens that the World Wide Web is a good way of doing this. So the person makes an announcement on a website that they have a file and they place a torrent file on the website which will let people know how to connect to him.
Once someone opens the Torrent file their Torrent program will open the torrent and retrieve the info and then connect to the person who is sharing and begin downloading the file. The person who has 100% of the file will only be uploading and is considered a Seeder, and a person who is downloading but doesn't have 100% of the file is a Leecher or Peer.
In the meantime someone else comes along and opens the same torrent file. That person connects to the original file sharer (seeder) and will also connect to the other downloader since they have visibility to them. The first downloader will also connect to the second downloader. So the original file sharer has 2 people downloading from him, and both peers will also be uploading any data they have to each other.
You can see that as more people start connecting to each other everybody will be sharing the file and as soon as you've downloaded the entire file you become a seeder. The main thing is that if you're downloading anything you will be uploading it at the same time. If the original file sharer turned off their computer it wouldn't matter because as long as there is one other person seeding.
A Web of Connections
Now, imagine that you want to download a file and there over 300 Seeders and 1000 peers. As soon as you open the Torrent file your Torrent program will automatically begin connecting to a multitude of Peers and Seeders. The files don't have to be downloaded in sequence so it doesn't matter who you connect to, as long as they have data you don't then it will be downloaded. It isn't hard to see why transfers via Torrents can give some great speeds.
Torrents are Special
So what's unique about torrents? There are 2 main appeals to Torrents:
No Hosting: If you consider the example above at no point in time was the actual file hosted on any server anywhere. If you have a 3GB file to share it isn't necessary that you upload it to a web server somewhere. Just make an announcement on a website, and people will be able to download.
Minimal Resources: If for example you had a 3GB file that you wanted to distribute and were expecting that around 1000 people would download it, that's over 3 terabytes of information. The cost to have a web server to host that file and download would be extremely expensive. Now, if you distributed the same file via Torrents, you would still need the server to originally host the file but the load on the server would be reduced as each person who downloads it would essentially be sharing the workload since they will have to upload at the same time.
These 2 examples may seem the same but both serve two different purposes. The benefit of No Hosting is that the file does not actually have to be sitting on a server anywhere, which is good if you don't want to make the file available on any web page. (This is really the benefit for copyrighted material). The second appeal really has to do with cost savings.
Issue of Copyright
Unfortunately, because Torrents are so well suited to transfer illegal files such as movies, TV shows, and games which tend to be quite large, it has received the attention of organizations such as the RIAA and MPAA. This has the effect of people associating Torrents with illegal downloads since they think it's another Kazaa or Napster. Even though Torrents are heavily used to transfer illegal files it doesn't mean there aren't people using this transfer method for legitimate purposes and I think we'll only be seeing more use of this technology in the coming years.
Just like any other protocol you'll need a client in order to begin using torrents. One of the most popular torrent clients is the Azureus : Java BitTorrent Client
. There are also others such as uTorrent
to name a few.