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When I download a torrent file there is an option for 'magnet link download'.

What is a 'Magnet Link'? Do they have any extra advantages?

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@Josh: Magnet links concern peer-to-peer clients, which are software. –  Ignacio Vazquez-Abrams Jun 27 '10 at 6:19
    
yes, valid question for me. –  akira Jun 27 '10 at 6:44
    
@akira:, ignacio: I guess I viewed it in a different context. –  Josh K Jun 27 '10 at 7:04

2 Answers 2

It is basically a link to a files hash signature not the files location. You can read all about it on wikipedia.

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A Bittorrent magnet link contains all the information needed to start downloading the files from peers directly. It is a server-less way of retrieving the right information to start downloading the requested files. A magnet link therefor is theoretically all that is needed to download files from other peers in the Bittorrent network. Magnet links can be distributed by email, messaging and other forms of communication but are most often found on the torrent sites that usually offer both torrent and magnet links to their users.

A magnet consists of several parts:

  • magnet: (This is the magnet link identifier)
  • ?xt=urn:btih: (Defines a Bittorrent Info Hash, the Edonkey identifier would for instance look like this xt=urn:ed2k:)
  • 5dee65101db281ac9c46344cd6b175cdcad53426 (The content hash)
  • &dn=name (The name of the file)

The full magnet link would look like this: magnet:?xt=urn:btih:5dee65101db281ac9c46344cd6b175cdcad53426&dn=download. Detailed information about additional Magnet Link parameters are listed on Wikipedia. One useful parameter that has not been mentioned yet is the as= parameter which contains encrypted information about a download source. This speeds up the process of finding the first peers.

Main Advantages of Magnet Links

The main advantage for Bittorrent indexers is that they do not have to store the torrents on their servers anymore which could be beneficial for them in several ways. It could reduce the pressure from the media creation industry and reduce hardware infrastructure expenses thanks to less tracking and downloading.

The end users on the other hand benefit from Magnet Links as well. All they need is the link to start downloading the files which makes them independent from torrent indexers. It also allows them to distribute the information more easily. Torrent indexers remain on the other hand the main source of information for new files that are available for download.

Magnet Links use DHT

A tracker less environment should raise a question of identification. How can a download be initiated ff there is no tracker to inform the Bittorrent user about other users who download and seed the file? The answer is DHT, Distributed hash tables. DHT is enabled by default in popular clients such as uTorrent or Vuze. Without going into to much detail, the hash of the magnet link is used to find peers using DHT.

Source

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