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Old 12-08-2003, 09:37 PM
randwill randwill is offline
Join Date: Feb 2003
Location: In the Minority
Posts: 3,498
What's the deal with Torrents?

I keep hearing that Torrents is the latest and greatest file sharing technology. Any Dopers up on this? Is it safe and better than regular peer to peer? Is the Man working to bring it down yet?
Old 12-08-2003, 10:12 PM
friedo friedo is online now
Join Date: May 2000
Location: Brooklyn
Posts: 23,592
BitTorrent is not really filesharing technology in the same sense of peer-to-peer programs like Napster or Kazaa, but it does use peer-to-peer technology for file distribution. Many individuals and companies that can't afford huge amounts of bandwidth use BT to distribute large files like software releases. Additionally, a lot of people distribute their short independent films via BT.

Here is a page that describes roughly how the system works. A much more thorough (but easily understandable) explanation is available here (PDF).
Old 12-09-2003, 12:29 AM
KP KP is offline
Join Date: Sep 1999
Posts: 1,789
In short crude strokes:

A torrent file contains information about a file - its size, name, 'announce server' and a hash code to confirm the accuracy of each segment you download. There can be different torrents for the same file (or set of files, in which case, the directory structure is specified, too) which may differ by only the announce server, segment sizes (and hence hash codes) or other single details, but each torrent file essentially describes a single way to download, and each torrent is as independent as a web URL [though, as you grow knowledgeable, you can alter a second torrent of an identical file to finish downloading]

Like Kazaa or Napster, but unlike FTP or HTTP, the servers do not contain the file you want to download. They only contain the info about *other* clients that are downloading the file or have finished downloading and kept the download connected for others to download. Unlike Kazaa or Napster, each file is 'connected' separately, rather than the program making everything in a certain folder or tree available to all comers.

Treat the torrent file as a URL. It is the thing that connects you.

Since you can download from many other clients at once (every client that is connected on a single torrent, and has downloaded even one complete segment should be sharing that segment), you can get high speeds by downloading from many clients at once (like kazaa, but in practice, much faster)

There is no single central search engine, as kazaa and Napster had. Some torrent sites do search one or more announce servers, but these together constitute a tiny fraction of the available Bittorrent files. Once you find a torrent, though, you should get downloads as fast or faster than Napster or kazaa. (Download speeds are very variable)

"leeches" is an insulting term in Napster/kazaa. It means someone who downloads but doesn't share. In Bittorent, though, anyone who hasn't downloaded and shared the entire file is a 'leech.', and those who have downloaded and are sharing complete files are called seeds. It is considered important etiquette to 'seed' a file for as long as you can after you finish downloading (or at least until you've uploaded 110-200% as many bytes as you downloaded) In Bittorent those with partial downloads are valuable, howeer, because they at least share the segments they've completed to date. Seeds are important, because if there is at least one seed, you will be assured of getting the whole file, while a tone of leeches might quickly get you to 99.9% but there may be one segement nobody currently online has.

A torrent where there are leeches that, together, don't add up to a whole file is called 'stalled'. A torrent with no seed or leeches is 'dead'. Even a single seed or leech online keeps a torrent 'alive' (useful) even if no one is downloading.from it. Eventually, though people stop connecting on that torrent (in days or weeks), and it is dead to all newcomers. Torrent servers can also drop a torrent as 'defunct', leaving it 'dead' , even if lots of people are trying to share
Old 12-09-2003, 01:03 AM
Mr2001 Mr2001 is offline
Join Date: Dec 1999
Location: Spokane, WA, USA
Posts: 7,213
Originally posted by KP
In Bittorent those with partial downloads are valuable, howeer, because they at least share the segments they've completed to date.
Incidentally, WinMX does the same thing. You might see a search result with "60% of 12,345,678 bytes".


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