Mac Happens

BitTorrent: Distributed File Sharing for Big Files

Evan Kleiman - 2004.11.17

File sharing is the newest rage in computing - the newest rage of about five years ago. And as file sharing's popularity grew, so did the technology behind it.

What's the latest trend with file sharing? The latest sending and receiving gem is BitTorrent.

What Is Bittorrent? How Does It Work?

BitTorrent is a program used for file sharing. Simple enough, eh? There are many other programs and technologies that you can use to download files with.

Most file sharing programs, such as LimeWire, use a technology called Gnutella. Loosely, Gnutella works by sending a request for a file to other computers on the Gnutella network. If someone on the network has the file, it is sent to you.

BitTorrent works a bit differently. You download a tracker file from a website and then use the tracker in your BitTorrent client (there's a list of a few clients at the end of the article). The tracker contains information about the torrent you'll be downloading.

Typically a torrent is either a folder or a zip file. The folder contains a set of files that are downloaded a bit at a time (hence the name), and each bit may come from a different source. This is useful to send a program or a whole CD at one time, as opposed to Gnutella, which can send only one file at a time.

When BitTorrent downloads a file (called a torrent), it sends and receives simultaneously. As you're downloading a section from one or more people, you're also sharing the bits you already have with others. This speeds up the process and keeps distribution high.

As with other peer to peer (P2P) networks, getting a file depends on having users currently online with that file.

How Is It Useful?

The biggest advantage is that you're almost always sending and receiving at the same time. You're unable to be a "freeloader" or "leacher," as it's termed in the rest of the P2P world, by not sharing anything. Forcing users to share what they're downloading puts makes more available at one time.

Of course, once it's downloaded, you don't need to share it any longer, although it's considered polite to do so for a while after completing your download. As I've said before, it's useful for sending an entire album or program instead of one file at a time.

How Do I Get Started?

There are many clients for sending and receiving a torrent file, such as Tomato Torrent (Mac only), Azurues (a Java client), or the official BitTorrent Client. Azurues offers the most bells and whistles. You get a good view of what's going on with the torrent you're downloading. The official client has a more straightforward interface. Tomato is somewhere in the middle. They all work pretty well, so you can choose one based on how much control you really want over your downloading.

Are There Any Downsides?

Well, first and foremost, there's no search function as compared to a regular P2P client like LimeWire. Instead, you'll need to find .torrent files on the Internet at places like Suprnova.

Since torrent files are normally larger than what you would download off of another service, bandwidth can become an issue. Copyright is another issue, one we won't cover in this article.

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