How do torrents work?
In: Technology
BitTorrent is a file sharing protocol, that is, a defined way for sharing files between computers. It works by splitting one or more files into several small pieces which in turn are shared with other users.
The main advantage of torrent is that when you have downloaded just one of these pieces, that piece can in turn be shared with other users immediately instead of having to wait for you to possess a complete file, meaning that a file can propagate very rapidly across a network of computers and without relying on a single server to do all the uploading. It also means that a download is very resilient against interruptions, since the torrent client can just count up the completed pieces when the download resumes and focus on the remaining ones. In the case of multiple files, certain files can given priority over others, for example the first episode of a TV series, leaving you to watch that while the rest are finishing.
Torrent is primarily associated with illegal file sharing, but it has also been [adopted in enterprise environments](https://tech.ebayinc.com/engineering/bittorrent-for-package-distribution-in-the-enterprise/) and even some MMO’s have used it to distribute patches.
Say you want a grand feast: burgers, pizza, and sandwiches for dinner. You want all this, but you don’t want to make it yourself or even go get it. Well, there are places that already have this stuff and will deliver it to you.
So you go to takeaway.com. You tell takeaway that you want your feast. Takeaway directs your request to Pizza Hut, McDonalds, and Subway, who all have parts of your feast.
When each place delivers their part of the order to you, your feast is complete.
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Torrents are much the same. Takeaway represents the tracker, which keeps track of hosts that have and are sharing what files. Your torrent file or magnet link direct your request to the tracker which helps redirect your request to the different hosts that are sharing it. Your computer and these hosts determine which host sends which parts of the file to you. When you have all the parts, the file is reassembled and your download is complete.
You want a puzzle so you download a map with the location of all the pieces and the location of everyone that has them. You then make your own copies of the pieces from people that are willing to share what they look like to make your own puzzle.
Let’s say you made a Kick-butt video game, and you decide you want to give it away for free. But it’s a big program, BIG! Server space and data transfer costs money, and you don’t want to have to pay every time somebody downloads it.
So instead you set it up as a torrent file. One person downloads it, and agrees to be a seed for the program, so now there are 2 sources. Then another person downloads it and is a seed, so that’s 3 sources (your original server, and the two people who have downloaded)
The more people who download and seed (share) the file, the more spread out the data transfer is. Instead of you being the only option, everybody who is seeding the program gets a little bit downloaded from them. Which can also help things move along nicely so one particular server doesn’t get bogged down with requests.
Now the end user has to have a torrent program because their program is downloading a chunk here and a chunk there from all these seeders, and it needs to be put back together properly. But that’s about the gist of it.
A torrent file tells the user’s computer details about the file that is to be downloaded.
The torrent client you are using then connects to a tracker which contains the IP addresses of other user computers.
Then you download your file in bits and parts from the other computers.
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