BitTorrent for Beginners

Comcast wants to kill it, your next wireless router will probably have it built-in, and you can use it to download the entire GeoCities archive. BitTorrent has come a long way since its public release on July 2, 2001, but unless you're a regular media pirate, you probably haven't used it much. Read on to find out how it works and to clear up a few common misconceptions about it.

Is BitTorrent Legal?

No court has found the BitTorrent protocol inherently unlawful. But using BitTorrent to trade copyright-protected files will likely put you on the wrong side of the law. A Princeton study published earlier this year estimated that only 1 percent of the files in a sample pool of 1021 files shared on BitTorrent were legal, so it's no wonder that many people assume that BitTorrent itself is illegal. To ensure that your downloads stay on the right side of the law, stick to trackers that are dedicated to sharing free content, such as ClearBits and LegitTorrents.info.

Though using BitTorrent is legal, several Internet service providers try to monitor users' traffic and clamp down on their BitTorrent usage. This is called "traffic shaping," and it can be highly inconvenient for torrent downloaders. Read "Elude Your ISP's BitTorrent Blockade" for more information.

How Does BitTorrent Work?

Normally, if you want to download a file from a Web site, you just click a few links in your Web browser and your system will start saving the file to your default Downloads folder. The server hosting the file sends you the file, bit by bit, until you have the whole thing.

Bandwidth isn't free, however, so transferring the file costs someone money . The more popular a file is, the more servers and bandwidth the hosts will need to continue distributing it. That's why so many downloads sites are saturated by obnoxious ads--the sites need to pay their bandwidth bills. As the world swaps larger and larger files, such as high-definition videos, high-resolution photos, and higher-quality music, the bandwidth bill grows and grows.

BitTorrent eases the monetary strain on individual file hosts by motivating downloaders to upload, too. If you're downloading a movie via BitTorrent, you'll start out downloading chunks of the movie. Once you've collected a few pieces of the movie, you'll continue to download the rest of the file, but you'll also start uploading the pieces you have to other people trying to download the same movie.

LinuxTracker lists the files, sizes, and number of seeders and leechers for each torrent.
For example, suppose that a movie file is split into four chunks named A, B, C, and D. One computer (the "seeder") has all four chunks, another computer has ABC, another has BC, and the last one has D.

As soon as you receive A, you can start sharing it with the other computers that don't have chunk A. The seeder computer can then use its bandwidth for sharing segment D, which is more scarce.

Also, the BitTorrent protocol rewards people who upload more files and upload files more quickly. If your uploading speeds are high, the client directs more people to send you missing chunks of your files.

Generally, BitTorrent makes it easier for users to share files at higher download speeds, but you may find that your Internet connection slows down while your BitTorrent client is open. That's because your bandwidth is being used not just for ongoing downloads, but also for simultaneous uploads. When your system has downloaded all of the chunks of a file, you don't need to worry about assembling the parts yourself.

The first step in downloading something with BitTorrent is to find a torrent tracker site, which is a searchable index of .torrent files. Each .torrent file contains the "metadata" for the file you're looking for; basically, the .torrent file tells your BitTorrent client how to identify the different chunks of each file and how they fit together.

The .torrent file isn't the actual movie, song, or other file you were looking to download. It's more like a decoder ring that sniffs out the different chunks of your file, then assembles them correctly once they're all downloaded.

If you're looking to download a Linux distribution, for example, you can just stop by LinuxTracker, find the torrent listing that matches what you're looking for, and download the corresponding .torrent file. Once the .torrent file is downloaded, you open it in a BitTorrent client such as Vuze or µTorrent (aka uTorrent), and you'll start connecting to everyone else who's uploading and downloading that file.

Just remember that if there are no "seeders" for that particular file, you won't be able to complete the download, because no one will have a full copy of the file. This doesn't happen often with popular files, but if there's only one person seeding your file, you might find your download has stopped because the seeder's PC shut down for the night.

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