"The people who have been fighting P2P file sharing systems, have turned a centralized system like Napster – easily controlled, easily monitored – into a fully decentralized system in the shape of Kazaa.

Worst, as a further consequence they have given conceptual fuel to the birth of a highly distributed ecosystem of thousands of centralized BitTorrent servers.

Photo credit: Jim DeLillo

Many diverse groups of people are embracing BitTorrent, and the number of sites hosting torrent files is growing by the day.

This fragmentation makes tracking down central sites difficult, if not impossible, and also shows how easy it is to host a front-end to torrents.

Bram Cohen, the 29 year old father of BitTorrent "realized that chopping up a file and handing out the pieces to several uploaders would really speed things up.

"Give and ye shall receive" became Cohen's motto, which he printed on T-shirts and sold to supporters." (Source: Wired article - The BitTorrent Effect)

One analogy to describe this process might be to visualize a group of people sitting at a table.

Each person at the table can both talk and listen to any other person at the table.

These people are each trying to get a complete copy of a book.

Person A announces that he has pages 1-10, 23, 42-50, and 75. Persons C, D, and E are each missing some of those pages that A has, and so they coordinate such that A gives them each copies of the pages he has that they are missing. Person B then announces that she has pages 11-22, 31-37, and 63-70. Persons A, D, and E tell B they would like some of her pages, so she gives them copies of the pages that she has.

The process continues around the table until everyone has announced what they have (and hence what they are missing.) The people at the table coordinate to swap parts of this book until everyone has everything.

There is also another person at the table, who we'll call 'S'. This person has a complete copy of the book, and so doesn't need anything sent to him. He responds with pages that no one else in the group has.

At first, when everyone has just arrived, they all must talk to him to get their first set of pages. However, the people are smart enough to not all get the same pages from him.

After a short while they all have most of the book amongst themselves, even if no one person has the whole thing.

In this manner, this one person can share a book that he has with many other people, without having to give a full copy to everyone that's interested. He can instead give out different parts to different people, and they will be able to share it amongst themselves.

This person who we've referred to as 'S' is called a seed in the terminology of BitTorrent." (Source: BitTorrent FAQ)

Unlike Kazaa, Gnutella, and any others, BitTorrent has a fundamentally “web-based” interface. That means you go to a website in your browser, click on a link from that trusted site, and download.

For each file, there is a central “tracker” that keeps track of what pieces of each file clients have, so clients can talk to each other and self-coordinate downloads more efficiently.

If you kill the BitTorrent tracker (see reference below), then you kill the ability of any client to trade files with others. It is for these reasons that BitTorrent is almost more similar to a direct-connect protocol like FTP or HTTP than to a P2P network like Kazaa.

To learn more about BitTorrent please see:
http://dessent.net/btfaq/

Wired - The BitTorrent Effect

What is a BitTorrent Tracker?
A BitTorrent tracker is the closest thing to a central server in a BitTorrent network. The tracker has two main functions; first, it organizes the downloaders of each file by telling each downloader who else is downloading that file. Second, it displays information about the files it's tracking by acting as a simple webserver. The original tracker can display each file's info hash, name, number of complete downloaders, and number of incomplete downloaders. If you want to see this information you can download a program called torrentspy from http://torrentspy.sourceforge.net, all you do is install this program and drag the torrent file into the applet. (Source: Peer Evolution Forums - Guide To Using BitTorrent)

The BitTorrent P2P File Sharing System - The Register

BitTorrent Search
TowerSeek.org is a true crawler-based BitTorrent search engine. Unlike other sites that simply mirror either Google's torrent search functions (try “filetype:torrent induce” for example), SuprNova, and other similar sites, TowerSeek employs its own web-based crawler to discover new and available Torrents.

BitTorrent software
http://dessent.net/btfaq/#where