BitTorrent, .torrent files, and how they work.

Why look at torrents specifically, as opposed to traditional downloads, or at what limewire does with its cache of various files? The answer brings us back to the fact that the The Pirate Bay (as well as a vast array of similar and semi-popular websites), uses .torrent filetypes to let their users download their files - dozens of popular sites just like The Pirate Bay exist, but for reasons stated in the original post, none of these will be referenced.

Let's see some guy with a peg leg figure this out. [Source]

In order to first understand what a .torrent is, one must first understand what the revolutionary BitTorrent protocol is. First and foremost, a protocol (such as HTTP or FTP) is essentially the explicit rules and properties that govern the transfer of data between computing systems - in essence an algorithm. BitTorrent varies from your "typical" File Transfer Protocol, which is essentially a linear process of copying information, in that  it requires seeders and peers (seeders being a subset of peers) to actively assist in copying bits and pieces of the original .torrent file in order to construct the complete file on a computer or system that is not hosting it.

A "peer" is anybody who is currently downloading the .torrent file, and therefore making it more readily available for users to download themselves. Every peer who downloads from the host is in fact hosting it themselves - bits and pieces of it, at the very least. Users who have completely finished downloading the file, but allow it to continue hosting it are known as "seeders", and are very conducive to faster download speeds for everyone else.

A "leecher" is any kind of peer who is detrimental to the "health" of a .torrent download. For whatever reasons, an individual may refrain from seeding once the download is completed, and deny the rest of the "swarm", as peers are collectively referred to, of another seeder. Additionally, users can throttle the speed at which their BitTorrent client downloads (and therefore uploads); this occurs fairly often when content is distributed illegally, such as on The Pirate Bay, because it makes the illegal download more difficult to detect.

The end result of this protocol is that the busier a .torrent file download is, the faster it completes. With a favorable ratio of seeders to leechers (anything around 1:1), a 3 gigabyte file can download in less than an hour. It's possible to download an entire band's discography in a matter of minutes.

 Nothing says technological advancement like hive-mind mentality. [Source]

That isn't, however, to say that BitTorrent is used only for illicit purposes - Facebook uses torrents to distribute updates to its servers. That very same article goes on to talk about how universities can reduce the number of servers necessary, because of the relative ease with which BitTorrent distributes files, which saves money in addition to time.