BitTorrent

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BitTorrent is a peer to peer file transfer protocol. It was created by Bram Cohen, who has since sold out. Fortunately, the protocol and the program itself were both open source, so many torrent clients exist today.

BitTorrent gains its strength from its decentralization. Anyone can set up a tracker and host their own torrents. It's important to note that none of the data that gets transferred via BitTorrent exists on the tracker. Torrent files (*.torrent) are small text files containing nothing but tracker information and hash information. BitTorrent downloads are often referred to as swarms. BitTorrent uses the upstream bandwidth from each client to help distribute the file (or files) to other clients, meaning that as more people join the swarm, the download will go faster for everyone.

Once you've completed your download, you become a seed. A seed is anyone in the swarm who already has the full file and can share any part of it out to anyone who hasn't completed their own download yet. Clients that haven't completed their download are referred to as peers, and derogatorily as leechers.

The hash information contained within the torrent file is used by the client to verify the integrity of the file as it is downloaded, meaning once your client says the download is complete, you have the exact same file as is on the computer of the person who started the torrent.

Using BitTorrent appears confusing to some, but is actually quite simple.

1. First, you need a client. A small list of common clients include:
   • Azureus
   • uTorrent
   • BitTornado
   • BitLord
2. Google for, download, and install one of those clients (or any other client, but some of the more obscure ones are ridden with adware/spyware. For this reason, always download a torrent client from its official website.)
3. Next, find a tracker with a torrent you wish to download.
4. Click the link that says "Download this torrent" or something similar.
5. Most modern BitTorrent clients will automatically pop up their own dialog box at this point, asking where you want to save the file. Choose a location, and start the download.
6. After some time passes, you will have what you wanted.
7. Be a good seed and leave it active for a while. The general rule of thumb is to wait until, at the very least, your share ratio is 1.

Share Ratio

Many BitTorrent users will stress the importance of the share ratio. This refers to the ratio of the amount of data you have uploaded to others vs. the amount of data you have downloaded from others. To show it mathematically:

 Amount uploaded
----------------- = share ratio
Amount downloaded

Usually, the mantra of "the higher it is, the better" is relied upon. What this means to the user is that you should try to seed torrents until, at the very least, you've contributed as much to the swarm as you've benefited from it, or a share ratio of 1.

Strengths

• Fast speeds for a peer to peer protocol
• Built-in error checking eliminates corrupt downloads
• Once the download is finished, you can use the file(s) immediately without having to stop the torrent, meaning you can continue to share to others in the swarm.
• Is an excellent protocol for transferring a large amount of data.
• Owing to its decentralized nature, finding something to download with your client is easy.
• Many torrent clients support scanning RSS feeds, and many trackers have RSS feeds. This means that by setting up a simple filter, you can have your torrent client automatically download things for you.
• Many companies (usually computer game developers) use BitTorrent to distribute trailers, patches, demos, and other files pertaining to their products.
• There are many legal torrents around the internet, for example, OpenOffice.org (a free and open source office suite similar to Microsoft Office) and most Linux distributions can be downloaded via BitTorrent.

Weaknesses

• To get the full benefit of the protocol, one must find an open port on their ISP. This takes a combination of luck and time, and can be very frustrating.
• People with routers will need to configure port forwarding.
• Works for smaller amounts of data, but not as well.
• People can enter and exit a swarm as they choose, so it may be impossible to complete certain torrents, particularly older ones.
• Dependence on people being good seeds and staying in the swarm after their own download finishes.
• While the protocol wasn't originally created for the purposes of copyright infringement, this is a fairly widespread use of it.

Pitfalls

• The more popular BitTorrent trackers are often targetted by copyright holders claiming infringement, even though trackers hold zero infringing data.
• ISPs like Comcast will mess with your torrent activity, causing downloads to go slower.