So what is a torrent exactly?
After having received numerous emails in the past that asked me to explain what a torrent is, I finally decided to write this little guide to help everyone who wants to know more about torrents, how they work and how you can use them. Many Ghacks reader without doubt know exactly how they can make use of torrents, and it is likely that this guide is not revealing any new information for them. I invite you to contribute to the article by leaving a comment below.
I first would like to address the different between torrent and Bittorrent, which is often used synonymously on the Internet. Bittorrent is a peer to peer (p2p) file sharing protocol that uses a swarm-like approach to file sharing. A torrent (file) stores metadata that programs like uTorrent use to download data to the PC it is running on.
What is a torrent?
The Bittorrent specification details the metainfo that are included in torrent files:
- announce - Lists at least one tracker url
- info name - Suggested name for the file or directory
- info piece - Files are split into fixed size pieces, and this defines the number of bytes of each piece.
- info pieces -Â A hash list
- info length - The length of the file
- info files path - A list of strings of subdirectory names and file names
- info files length - The actual file size in bytes
When you download a torrent file and add it to a downloader such as utorrent or qBittorrent several things happen in the background. The Bittorrent client tries to establish a connection to the tracker to receive a list of peers that are currently transferring pieces of the file. This can be users who are downloading the files associated with the torrent currently, or seeders who already have downloaded the complete data and are now making it available to all downloaders. The speed usually improves with popularity of a download.
When you add a torrent to a program compatible with Bittorrent, you receive a wealth of information. The popular uTorrent client for instance displays the number of pieces and files, the peers you are currently connected to, the trackers, and the hash among other information.
Every user who has started downloading the file and has downloaded at least one piece can also be a seeder for that file. The idea here is to accelerate downloads by using swarm technologies. While there are ways to artificially limit your own upload speed or use modifications that prevent the seeding of files, the majority of users are both downloading and upload pieces of files they are interested in.
The local client downloads pieces from different users to assemble the files once all data pieces have been downloaded to the system.
You may also encounter magnet links on some sites that may have replaced torrents on those sites, or may be offered in addition to torrent files. A magnet link is a web link that contains metadata that Bittorrent client can use to start downloading files. The benefit for sites that host torrent files is that it is reducing the bandwidth needed to operate the site. While torrents can reach a size of a Megabyte or more, a link reduces that to less than a Kilobyte of data.
How to download a torrent
It is actually pretty easy to download torrent files. All you need is a program that is supporting the Bittorrent protocol. This can be a web browser like Opera, or a program designed specifically for the purpose like uTorrent. The programs usually register the .torrent file extension on your system so that all torrent links that you click on are automatically added to the application.
If that is not the case, you can drag and drop the torrent files from the local system to the application to start the download.