A Beginners Guide To BitTorrent

Posted on 24/04/2008 under Old Guides

Note: this article is old and may not still be relevant.

A little about BitTorrent

BitTorrent is a type of peer-to-peer (P2P) network, which enables users to share files over the internet. This includes, but is not limited to: Music, Video, Images and Programmes. BitTorrent is was created by programmer Bram Cohen, and is designed to distribute large files efficiently. BitTorrent is open source, and can be used on any platform.

How it works

BitTorrent clients are programs which implement the BitTorrent protocol. Each BitTorrent client is capable of preparing, requesting, and transmitting any type of electronic file over a network using the BitTorrent protocol. The image below illustrates how a file is shared between a users computer other users (peers). This distribution is controlled by a server called a ‘tracker’. (I may or may not update this sketch, I haven’t decided yet!)

To begin with, a torrent file (file extension ‘.torrent’) is created and contains information such as what file is being shared, and what tracker is associated with it. The torrent file can then be passed on to other users, who can download the file, and begin uploading to other peers simultaneously. On a larger scale, the torrent file can be uploaded to a website, and downloaded by anyone.

Finding the file you want

BitTorrent is useful for sharing files among small groups of people, by distributing the .torrent via email and chat programs. However, a major benefit of BitTorrent is that these files can be uploaded to websites (called Indexers), and users are able to search torrents for the file they are after. Some such websites are: www.thepiratebay.org www.BitTorrent.com www.torrentspy.com www.mininova.org In this example, I did a quick search for ‘Adium’ on piratebay which is the chat program I use on my mac. This can be downloaded for free from www.adiumx.com . One result came up, and once selected, the torrent details were displayed as shown below.

As BitTorrent relies solely on the community for upkeeping, alot of information is displayed about the torrent. Users can rate, or comment on the file after they have downloaded, and this helps other users when searching for the file they want. Other information which is usually displayed are who submitted the torrent, how many times it has been downloaded, the numbers of seeders (uploaders) and leechers (downloaders) at that time and trackers can also be listed (although not in the example above).

How to download

Once you have found the torrent you want to download, you need a copy of that torrent on your local machine. This means you need to click the link to download the torrent. You now need a BitTorrent client to use this file and download yor data. There are many availible, some of the better ones I have come across are below. BitTorrent (cross platform) Transmission (most platforms… except windows!) Azureus (cross platform) ABC (windows only) µTorrent (windows only) I highly recommend Transmission, or the official BitTorrent client if you are a windows user as they very simple to use. Depending on which one you use, these programs can have alot of advanced features. I use Transmission, which is the best client I have used to date. I aim to write more about the different applications available in another article. Once you have your client downloaded and installed, you can use it to open your BitTorrent file. This is as simple as File > Open! Depending on which client you use, you may need to set up some preferences, but in the example below, ‘BitTorrent OSX’ only needed to know where to save the data to, and it was away!

The image above was taken on a mac, so it may look different on your machine, however the operation is the same. As you can see, the interface is quiet straight forward. Details about the download are shown – including a progress bar, download speed, how many seeds / leeches, and estimated time till the torrent is complete. If you have more then one torrent downloading, it will be displayed in the same list. Don’t be surprised if a torrent starts off slowly. Sometimes it takes a while to gather momentum. Once the file has finished, the completed file is ready to use. Now you’re done! Don’t forget to seed after the torrent has finished! More information…

The Jargon

.torrent: A .torrent file contains all the info you need to download the file you want. Client: A program used to ‘load’ the .torrent file so that you can connect to other people. Indexer: Indexers are websites which list (index) .torrent files Piece: A large file is broken down into smaller pieces. The size of the pieces depends on the size of the file as a whole. Health: A torrent is kept healthy by people seeding as much as possible during their download, and after it has completed. Lack of people sharing in this manner will cause a torrents health to lower, and possibly to die-out. Leecher: A leecher is someone who is downloading (and uploading) a file. You are a leecher if you do not have a complete copy of the file you’re trying to get. Peer: A peer is the same as a leecher, but without the negative connotation. Ratio: The data you uploaded divided by the data you downloaded. Ratios above 1.00 means that you have uploaded the complete file, and more. Scrape: Scraping is your client client requesting info from the ‘tracker’ about peers, and more importantly about your progress. Seeder: A seeder is someone who has a complete version of the file you are downloading. If there are no seeders, you probably wont be able to get the file. So seeders are extremely important, make sure to ‘seed’ the torrent once you finished downloading. Tracker: The tracker is a server that has all the info about the people that are down- and uploading the file. The tracker itself does not have a copy of the file, it only tracks the up- and downloaders and makes sure people are able to connect to each other. A tracker is not the same as a website that hosts torrents. Super-Seed: Some clients have the option to ‘super-seed’. Super seeding is different from seeding because it tries to send out pieces of the file that have not been sent before. So instead of sending the same piece to several peers, it tries to send a unique piece to everyone so that other peers can swap those pieces. Swarm: The swarm are all seeds and peers that are connected together. So if your client shows 5 seeds and 10 peers then that’s your swarm.

FAQ

Where does ‘BitTorrent’ come from? ‘Bit’ refers to the binary data which makes up electronic files. ‘Torrent’ describes how the transmission of this data is done, like a flowing stream. What do people mean when they talk about the health of a torrent? This is related to the upload and download statistics of a torrent. The more seeders and leechers there are, and the better the ratio (i.e. the number of seeders : leechers) – the healthier a torrent is. The health of a torrent is therefore closely related to download speeds. Why do the files take up so much room straight away? Because of how BitTorrent reads to/from the file, space is allocated as soon as a torrent starts. The file will not be in a usable form until the very last piece is downloaded. Do I have to upload? The working of BitTorrent relies upon people uploading as well as downloading, and also continuing to seed once the file has completed. That said, this is not a requirement for downloading, although a minimum upload is set in most clients. What is a share ratio? This is the amount uploaded/ the amount downloaded. Once your ratio is up to 1.00, you have completely uploaded the data once.

Legality

Although large BitTorrent sites make available torrents to copyrighted data, they do not actually store any copyrighted data, and so are not breaking any laws as such. It is therefore the users who decide to download such data that are breaking the law. This said, a number of BitTorrent websites have had their premises raided, sites taken down, and law suits filed due to claims of copyright infringement.

What to avoid

Like any part of the internet, there are people out there who aim to harm your computer by spreading malicious files. Always read what you are downloading, and check the comments if possible. Checking the torrent name matches the file you are downloading is also a good idea. If you are unsure, don’t download! Because any files can be shared through BitTorrent, alot of adult content is available. This is often hidden, and requires registration to access – but not always.

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