In the fall of last year The Pirate Bay took its tracker offline. Luckily, for the stability of the BitTorrent ecosystem several new trackers emerged to take its place. Time for us to provide an overview of the largest public BitTorrent trackers currently around.

The BitTorrent landscape has changed dramatically in the past 12 months. The two largest BitTorrent trackers today didn’t exist a year ago, and the top tracker of last year has shut down. The upside is that all these changes went by relatively unnoticed to the millions of downloaders.

Despite claims that millions of BitTorrent downloads would cease to work if a major BitTorrent tracker closed down, most downloaders today don’t even notice when a tracker stops working. Thanks to technologies such as DHT and PEX central trackers have become a luxury good to some degree.

Indeed, larger torrents with thousands of peers will work just fine without a central tracker. But the majority of torrents out there only have a handful of peers and for these files a central tracker is still an essential part of the downloading process.

It’s therefore good to know that several new players took the place of The Pirate Bay’s tracker when it shut down last year. Below we show a list of the five largest public BitTorrent trackers based on the number of torrents and peers (downloaders+uploaders) they track.

5 Largest BitTorrent Trackers, June 2009 # Tracker Torrents Peers Software torrentfreak.com 1 PublicBitTorrent 2,484,145 21,694,091 Opentracker 2 OpenBitTorrent 2,388,738 21,186,589 Opentracker 3 Denis.Stalker 1,614,356 10,527,993 Opentracker 4 1337x.org 302,799 4,889,991 XBT 5 Torrent.to 326,467 3,205,170 Opentracker

The first thing that stands out in the top five above is that the first three spots are taken by standalone trackers that do not have a torrent index or search engine attached to them. These three trackers are responsible for the coordination of millions of public downloads on BitTorrent but do not provide any torrents on their sites like The Pirate Bay used to do.

PublicBitTorrent and OpenBitTorrent, number one and two in the list, are both relatively new trackers that emerged after The Pirate Bay announced that it would sell the site last year. This sale eventually failed to go through, but The Pirate Bay did close its tracker so both trackers became a very welcome addition to the BitTorrent ecosystem.

Another observation is that there is a lot of weight on the shoulders of the top three trackers. Although there are close to 50,000 known BitTorrent trackers, only a fraction of these are active, and of these only a few dozen track more than 1,000 torrent files. Without the five trackers in the list above most of the smaller public torrents could quickly become unavailable.

Although trackers in the top five are all public ones, there are a few private ones that should be in this list if it was only based on the number of torrents tracked. The music tracker What.cd, for example, currently tracks more than 800,000 torrents alone. A dazzling number that puts the site in fourth place based on the number of torrents, not peers.

For BitTorrent’s long tail content reliable public trackers are still invaluable. The good news is that the ecosystem is better off than a year ago when The Pirate Bay was carrying this burden alone, but it’s far from bulletproof yet.