All about torrents

Since the onset of the Internet, people have exchanged information of many kinds and sizes. At first, this was usually done through the email or downloading software, but, as multimedia content became larger and more available year after year, people started looking for other ways to exchange it. The issue was that really large files would require good hosting servers, and a large amount of bandwidth to be shared (else, many users would experience slowdowns, or problems due to a server saturation). An American man named Bram Cohen invented what is now known as the BitTorrent protocol to solve this problem.

The BitTorrent protocol divides a large file into small chunks, allowing users to download sections of it and to exchange the sections between themselves until the file download completed. This protocol uses a lot less bandwidth from the file's creator, and is a great advantage for its distribution in the long term.

How it works

A seeder, who has a large file to share starts by creating a set of instructions called the torrent file. The torrent file stores information about the file itself, and includes information about the trackers the BitTorrent protocol will use. These trackers are like referees or coordinators. They will arrange which user downloads which part of the file first, and coordinate the subsequent downloads and exchanges.

The download process starts when another person wants the file that the seeder is sharing. He will then download the torrent file, and open it with a torrent client. The torrent client will then connect to the trackers appointed by the seeder and get into a sharing network, called a swarm. Once the torrent client has done that, it will start downloading sections of the large file one after the other following the tracker instructions.

What makes the torrent special is that the client will not only download from the original seeder. It will be able to download some sections from other peers as well. Actually, that's what the tracker does. It coordinates which user (called a peer or leech) has each section of the file, so that you can download different sections of the file from different people. Sure this means you will upload a few sections of the file too, but there isn't anything to worry about during a torrent exchange: You will download sections of those files specified in the torrent file only, and you will upload sections of those files only too. Your latest school or work documents will never be shared, exchanged or otherwise affected.

This also means it is pretty unlikely to download a virus from a torrent service. For this to happen, the virus would have had to be included in the torrent file in first place, something nobody does.

Eventually, you will get all the sections of the file and complete it. That will make you a new seeder of the file for the rest of the community.

Have you got questions? These are the most usual...

What kinds of files can you upload and download with the BitTorrent protocol?

You can upload what you seed and download any file someone else has placed in a torrent file. To get torrent files, you will usually make use of a torrent files search engine.

If I get the file in sections, how do I know all the sections will be the correct ones?

Part of the protocol includes a check for each section you download. If this check fails, the whole section is discarded and downloaded again.

Is BitTorrent fast to download?

A BitTorrent download will usually start slow (because trackers try to keep it fair between how much you download and how much you upload to the swarm in exchange, and you don't have much to share yet), then speeds up like you rarely see with other downloads.

How does the tracker choose which section will I download first?

The tracker will have you download the section which is scarcer for the rest of the community first. That way, the integrity of the download will not be affected if a member of the swarm leaves.

Can I just finish downloading and disconnect?

In theory yes, but it is a good idea to keep sharing. It is the spirit of the BitTorrent protocol and its communities.

The BitTorrent client says it will take a week to download!

No problem, the good thing about torrent downloads is that you can pause them. You can start a download today, stop it, turn off the computer, go to sleep, turn on your computer the next day, and continue downloading. Nothing will be affected.

I am ready to start

To wrap things up, you can start using torrents following three easy steps. You start by getting a BitTorrent client. Next, you get the torrent file of what you need or wish to download. Lastly, you click and begin downloading.

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