A bit on bittorrents

March 28, 2008 7:04 AM

Can someone explain to me the magic of bittorrents?

How do they work? How are they different from programs like Limewire and Kazaa? What's the deal with seeds and peers and how can you optimize your downloading speed (i.e. how to make it quicker)? Finally, which are the best sites where you can find downloadable files? Thank you.

posted by barrakuda to computers & internet (14 answers total)

Instead of downloading from a single source, the swarm of clients downloading the file(s) uses the tracker to find other peers and negotiate parts of the file(s) from them instead, decreasing the burden on a single source for the file(s) and increasing the overall transfer speed for the users.

It's also relatively easy to use -- Just get the .torrent, open it with your client, and let it run til it finishes. There's more to it but that's the basic idea.

If you want to download/upload faster, look into forwarding ports if you're using a NAT router.

I'm not going to provide links to download sites but with casual surfing you'll be able to find the most popular sites with ease.
posted by arnold at 7:08 AM on March 28, 2008 [1 favorite]

What do you want to know that's not here?
posted by Wolfdog at 7:09 AM on March 28, 2008

See if this AskMe Q helps.
posted by daksya at 7:10 AM on March 28, 2008

Wikipedia entry.

Seeds are people who have the whole file, peers are those still grabbing it (i.e. they have part of it, and since you are downloading parts from multiple sources, you can be getting the parts a peer has from them).

As for optimising - keeping an eye on how many sources your client is set to connect to is the best way. I find that some torrents will seem to bog down my incoming connections, and others I am getting less data in than I would expect. So sometimes I will set my max. connections to about 400, then other times I have to bring it down to 100 just to get the kind of download rates I expect (from my connection that is). It takes experimenting, but you ought to get the hang of it.

As for where to look, Scrapetorrent will search multiple sites for you which I find handy. Basically though I only grab torrents that originate from BTJunkie, Mininova, The Pirate Bay, and occasionally one or two others.
For TV it's also well worth checking EZTV, as they are one of the better sources of the torrents as they go up in the first place.
posted by opsin at 7:13 AM on March 28, 2008 [2 favorites]

If there's an objection to me posting links to those sites, please do edit them out. The optimising paragraph is really what I was posting for.
posted by opsin at 7:15 AM on March 28, 2008

Kazaa and Limewire (unless I'm wrong) are P2P (peer to peer) file exchange programs - basically you are sending/receiving files over a 1-to-1 connection. Your download can only be as fast as the other ends upload speed. If you are downloading a file from someone who has 15 other users connected to him, your speed will suffer.

Bit torrent on the other hand is a "Swarm" type of technology. When you start downloading a file, it grabs pieces of that file from multiple sources and reassembles them. This enables the download to be many times faster, especially useful for large files. If a torrent is popular, and you catch it during a time where it has many "seeders".. you can experience some amazingly high download rates.
posted by jmnugent at 7:34 AM on March 28, 2008

Lifehacker's guide (also a lot of other good bittorrent resources)

To find files, I find that the best site is Pizzatorrent
posted by nameless.k at 7:34 AM on March 28, 2008

Kazaa and Limewire (unless I'm wrong) are P2P (peer to peer) file exchange programs - basically you are sending/receiving files over a 1-to-1 connection.
posted by jmnugent

Limewire allows multiple people downloads....so you can be downloading from up to eight (I think) people at once.
posted by Grither at 8:05 AM on March 28, 2008

How Bittorent Works by Sam Hughes
posted by aheckler at 8:32 AM on March 28, 2008

How do they work?

Google can tell you. It's beyond the scope of an AskMe question.

How are they different from programs like Limewire and Kazaa?

BitTorrent is not a tracker. A torrent involves the distribution of a single file (or bundle of files), and knows nothing about whatever other torrents you may be running. You need to go to an external source ("trackers") to perform aggregate functions like search. In contrast, this aggregate search is built in to Gnutella and Kazaa. When you are downloading multiple torrents, you are actually participating in multiple P2P networks.

What's the deal with seeds and peers and how can you optimize your downloading speed

You can increase your downloading speed by uploading more. Peers will send more to you if you send more to them. A seed is a machine which has the complete file already; a peer is still trying to collect all chunks of the file.

BitTorrent is designed to be resistant to attempts at cheating this mechanism, so you're not going to be able to easily increase your speed unless you buy a faster upstream connection.
posted by qxntpqbbbqxl at 9:03 AM on March 28, 2008

Short form - bittorrent allows downloaders to share the wealth as they download, helping one another rather than forcing the download source to bear the entire burden.
posted by zippy at 11:02 AM on March 28, 2008

With bittorrent, you make explicit that you're sharing some particular file.* Lots of people have unwittingly released large chunks of personal data to the world with other P2P protocols and clients by not understanding their defaults and making their whole drives, or some large portion thereof available for download. (I don't mean this as FUD for other protocols -- make sure you understand their settings and defaults and you'll be fine.)

Bittorrent works much, much better when allowed to use a range of ports than if it's struggling to use just one. This may require configuration in your OS, firewall, and/or router. Here's some advice on settings to optimize bittorrent in DD-WRT. (There are some relevant things to increasing performance outside of getting a fatter pipe.)

Where bittorrent really shines is for large things with bursty demand, like a new release of a popular Linux distribution. Before bittorrent, such a new release would often cause server meltdowns and all the downloaders being miserable for weeks until the demand had ramped down enough for the servers to perform reasonably. With bittorrent, the larger the demand, the more distributed the load is, so it gracefully scales with very large demand.

Bittorrent's speed advantage doesn't hold for an individual downloader (versus the individual's trying to download from a non-overloaded server whose upload speed is at least as fast as the individual's download speed.**) What is true is that the total number of downloads it allowed in a short amount of time for things in high demand was much greater than the alternatives, due to avoiding the server-meltdown thing. This was revolutionary when it was new; I don't know to what degree other networks are doing similar things now.

* Of course, it's possible that someone could write some excessively bozotic bittorrent program that automatically announced to a tracker that it was seeding everything on your drive. I haven't heard of this happening.

** Glossing over a ton of details...
posted by Zed_Lopez at 11:04 AM on March 28, 2008

How Bittorrent Works on HowStuffWorks.com
posted by braveterry at 2:53 PM on March 28, 2008

I asked a question about peer-to-peer filesharing a while ago that had some good answers.
posted by CrazyLemonade at 3:15 PM on March 28, 2008