To download something with BitTorrent or any other Torrent fetching Engine, you must have a .torrent file. This file contains in it the location that tells the BitTorrent client where to go to find the tracker that manages the uploading and downloading of the archive. An archive is a complete set for downloading which may include one file or many files.
The one .torrent file contains the archive information also. To download on this network it is simply a matter of clicking on the .torrent file in your web browser, then the BitTorrent client kicks in and asks where you'd like to save the archive. That's it, from there you just sit back and watch the client work it's magic.
BitTorrent is a distributed file distribution technology. When you download a file using BitTorrent, the file is actually broken up into chunk that your BitTorrent client program then downloads and reassembles into the final file as the pieces arrive. To over-simplify, what makes it interesting are two things:
The different chunks you download can all be coming from different machines. A BitTorrent client will connect to many other BitTorrent clients and download several chunks at once, in random order. In the long run this makes the protocol fairly efficient, and very nicely scalable - the more BitTorrent clients that are serving up a given file, the faster other clients can download it.
As you start collecting chunks of the file, your BitTorrent client will start making those chunks available for downloading to other BitTorrent clients, and will become a part of the peer-to-peer file distribution network.
The file is downloaded piece by piece from one or many different sources. It's efficient because you get faster downloads using a lot less bandwidth. Let us see how?
Traditional Client-Server Downloading
To understand how BitTorrent works and why it is different from other file-serving methods, let's examine what happens when you download a file from a Web site. It works something like this:
You open a Web page and click a link to download a file to your computer.
The Web browser software on your computer (the client) tells the server (a central computer that holds the Web page and the file you want to download) to transfer a copy of the file to your computer.
The transfer is handled by a protocol (a set of rules), such as FTP (File Transfer Protocol) or HTTP (HyperText Transfer Protocol).
Client-server download process
The transfer speed is affected by a number of variables, including the type of protocol, the amount of traffic on the server and the number of other computers that are downloading the file. If the file is both large and popular, the demands on the server are great, and the download will be slow. Most of the times if the connection interrupts it is not resumable too. A lot of downloading gone in waste.
Peer-to-peer File Sharing
Peer-to-peer file sharing is different from traditional file downloading. In peer-to-peer sharing, you use a software program (rather than your Web browser) to locate computers that have the file you want. Because these are ordinary computers like yours, as opposed to servers, they are called peers. The process works like this:
You run peer-to-peer file-sharing software (for example, a Gnutella program) on your computer and send out a request for the file you want to download.
To locate the file, the software queries other computers that are connected to the Internet and running the file-sharing software.
When the software finds a computer that has the file you want on its hard drive, the download begins.
Others using the file-sharing software can obtain files they want from your computer's hard drive.
Gnutella's peer-to-peer download process
The file-transfer load is distributed between the computers exchanging files, but file searches and transfers from your computer to others can cause bottlenecks. Some people download files and immediately disconnect without allowing others to obtain files from their system, which is called leeching. This limits the number of computers the software can search for the requested file.
What is a leecher?
A leech(er) is a client on the BT network that does not have a complete copy of a particular archive yet. When any new client begins downloading an archive, they are a leecher until they have finished downloading the entire archive and then become a seeder. The name 'leecher' here is an unfortunate use that has become too commonly used even though it is really not applicable to what the meaning is. A leecher normally means someone who downloads without uploading (takes but does not give.) But here, a leecher is part of the network and is uploading as well, many times more KB than they download. But hey, it's worth the new meaning once you appreciate the vast resources that BT brings to you.
What is a seeder ?
A seed(er) is a client on the BT network that has a complete copy of a particular archive. For any archive to work, there must be at least one seed to download from originally. Sometimes under certain circumstances, there may be no one seeder but enough people with all the parts to make up the whole archive, this is called a distributed copy. It is HIGHLY recommended that once you have gotten an archive you leave the BT client running for at least the amount of time that it took you to download the archive to help ensure that others will also be able to get it.
What is a tracker?
A server that keeps track of the peers and seeds in a swarm. A tracker does not have a copy of the file itself, but it helps manage the file transfer process.
Significance
Torrents open the doors for swifter and wider file sharing. Many reputable software distributors choose to release their products via torrent files in order to reduce strain on their servers. This method of distribution also helps independent and smaller software companies or artists who do not have as much capital at their disposal to create physical media.
Warning
Though few casual Internet users ever find themselves in legal trouble for downloading pirated music, many ISPs closely monitor the type of data that is uploaded. The majority of cases in which an individual was prosecuted on charges of file sharing involve the user sending illicit music files rather than receiving them. With a torrents, uploading data is often a prerequisite for downloading files. As such, you are much more liable for being implicated for software or music piracy by utilizing torrents.
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