Take the 2-minute tour ×
Super User is a question and answer site for computer enthusiasts and power users. It's 100% free, no registration required.

What's the difference between a torrent file and a Magnet link?

What is the difference between usage, can I use μTorrent to download files from a Magnet link?

share|improve this question

3 Answers 3

up vote 14 down vote accepted

μTorrent is compatible with Magnet links, so you can use them.

Short version:

Instead of downloading the .torrent file from a webserver, you download it directly from a seed/leecher. The biggest advantage is that you might be able to download the content of the torrent, even if the tracker is down or closed for registration.

Long version:

Traditionally, .torrent files are downloaded from torrent sites. A torrent client then calculates a torrent hash (a kind of fingerprint) based on the files it relates to, and seeks the addresses of peers from a tracker (or the DHT network) before connecting to those peers and downloading the desired content.

Sites can save on bandwidth by calculating torrent hashes themselves and allowing them to be downloaded instead of .torrent files. Given the torrent hash – passed as a parameter within a Magnet link – clients immediately seek the addresses of peers and connect to them to download first the torrent file, and then the desired content.

It is worth noting that BitTorrent can not ditch the .torrent format entirely and rely solely on Magnet links. The .torrent files hold crucial information that is needed to start the downloading process, and this information has to be available in the swarm.

share|improve this answer
    
do you mean to say that uTorrent can ditch the .torrent format entirely and rely solely on Magnet links? –  Pacerier Aug 28 '11 at 17:26
    
According to last paragraph, no. –  Saxtus Aug 29 '11 at 14:06
    
i mean uTorrent not bittorrent.. –  Pacerier Aug 29 '11 at 21:51
    
μTorrent still has to store things not included in a magnet link, because it needs to track the progress of the downloaded file. Magnet link is just a link, you can't store progress info in it... –  Saxtus Aug 30 '11 at 13:21
    
Wikipedia mentions a required "availability search" to find peers (and the actual file). Where does the client look? Does a magnet link require a tracker URI or is that up to the client's network? –  Rudie Feb 20 '13 at 19:02

can I use μTorrent to download files from a Magnet link?

Yes, you can.

Both torrent file and Magnet links perform the same task, that is, download files via BitTorrent. Magnet links contain hashes of the files to be downloaded and location of where these can be downloaded from.

From the Wikipedia,

Magnet links consist of a series of one or more parameters, the order of which is not significant, formatted in the same way as the query string on the end of many HTTP URLs. The most common parameter is "xt", meaning "exact topic", which is generally a URN formed from the content hash of a particular file, e.g.. magnet:?xt=urn:sha1:YNCKHTQCWBTRNJIV4WNAE52SJUQCZO5C

referring to the Base32 encoded SHA-1 hash of the file in question.

Other parameters defined by the draft standard are:

  • "dn" ("display name"): a filename to display to the user, for convenience
  • "kt" ("keyword topic"): a more general search, specifying search terms rather than a particular file
  • "mt" ("manifest topic"): a URI pointing to a "manifest", e.g. a list of further items application-specific experimental parameters, which must begin "x." The standard also suggests that multiple parameters of the same type can be used by appending ".1", ".2" etc. to the parameter name, e.g.

magnet:?xt.1=urn:sha1:YNCKHTQCWBTRNJIV4WNAE52SJUQCZO5C&xt.2=urn:sha1:TXGCZQTH26NL6OUQAJJPFALHG2LTGBC7

share|improve this answer

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

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.