Who would have guessed that Bram Cohen's peer-to-peer communication protocol could ever achieve this kind of success? Even the man himself probably couldn't have forecast its popularity when he designed the BitTorrent protocol in April 2001. However, the protocol as well as the client applications started to mature from early 2004.
"When I first started working on it, nobody knew whether it was possible to overcome all the logistical problems of handling a flash crowd. It was challenging, but not only did I get it to work at all, but got it to work extremely efficiently. More recently, I'm proud of being part of the team that has worked hard to convince content publishers and enterprise businesses that unlike other p2p architectures, BitTorrent is a legitimate and incredibly powerful tool for content delivery." -Bram Cohen
Simply put, the glory days of the BitTorrent (abbreviated BT) protocol started in 2004 and its veneration is still steadily growing on an exponential level. In terms of importance, the BitTorrent protocol virtually crushed and eliminated all of the other contemporary file-sharing solutions. P2P networks such as Direct Connect (DC++), eDonkey (eMule), FastTrack (Kazaa), and Gnutella are all things of the past. It's rather impressive that according to some of the most recent statistics done by Evidenzia (an enterprise that specializes in collecting, analyzing, and archiving the traffic of P2P networks), the number of files that are released under the BitTorrent protocol have nearly tripled compared to last year. As a result, in Q3 2007, BitTorrent reached a peak milestone.
This being said, we think that it's a priority to dedicate an article to reviewing two of the most popular BitTorrent clients. At first, we're going to give you a brief overview of BitTorrent networks, how they work, what clients are for, and ultimately explain the most important terminology: seeds, peers, swarm, tracker, leech, etc. Once you're familiar with the tidbits of this P2P protocol, we can move on.
You can already anticipate reading a comprehensive comparison of the following standalone BitTorrent clients: Azureus and μTorrent. As a result, we guarantee that as soon as you finish reading this article you will be hooked up with the necessary knowledge and information to feel at home in the world of BT networks.
Now that you're prepared, let's begin with the brief introduction, general terminology, and then continue with the all-embracing and in-depth review of those aforementioned freeware clients.
BitTorrent by its very nature is a peer-to-peer protocol designed for transferring files. It works on the methodology of multiple users uploading and downloading small segments as parts of a file or files. The client is a software application that enables the user to take advantage of the BitTorrent protocol. It communicates through it. The central server that manages the connections is called the tracker. Basically, it logs the seeds and peers that are in the swarm. It is really important to point out that the tracker does not have copies of the files; therefore, it cannot be involved directly in the data transfer. The tracker exchanges information with the clients. That is its job. In BT terminology, a peer stands for an instance of a BitTorrent client that is connected to the Internet and is able to accept connections from other clients. By definition, a peer does not have the complete file yet, just parts of it. Nevertheless, if the client has the complete file and offers to upload it, then we call that a seeder. Other terms that you should be familiar with are leech, lurker, share ratio, swarm, and snubbed. The swarm is the combined group of peers and seeders that share a specific file. Therefore, all of the clients that are involved in the data transfer are building up a swarm. The leech is a person that downloads more than uploads. This is when the share ratio of a leech is called poor or negative (it's below 1). Share ratio is calculated as follows: total uploaded/total downloaded. That's why below one means that the leech downloaded more than uploaded and thereby has a negative effect on the swarm. A lurker is a seeder that does not add new content. By no means should a lurker be confused with a leech because the lurker seeds all of the already downloaded files. Furthermore, the term snubbed is used to describe a client that does not upload any data for more than 60 seconds, for whatever reason. This is a flag that works based on the feedback given by downloading clients. Last, but definitely not least, we need to introduce the torrent file. It's a file that contains the metadata (name, size, checksum) of the files that the particular file makes available to download. The metadata also contains the address of the tracker that organizes the connections between peers and seeders. In general, this file sports a .torrent extension. Now that we've covered all of the required BT terminology, let's talk a bit about how the system works and why it's so effective. Sharing content directly via websites is a very challenging approach, even though umpteen mbps bandwidth services are dominating. Keeping up with the high number of downloads is a headache for network and system administrators. The sharing option is definitely not a cheap one. The underlying reason that supports the development of the BitTorrent protocol is that it popularizes the technique so that users are both uploaders and downloaders. The file is split into numerous segments and the redistribution approach is usually the "rarest first" or random. The more users are seeding the content, the higher the transfer speed gets and healthier the swarm becomes. The server acts just like a manager (tracker). It really makes sense that organizing exchanges between users and hosting metadata files, which are very small in size, is very efficient and less resource-dependent than hosting the file as a whole and handling all of the work. As a result, file-sharing gets decentralized and the bandwidth of the central server is freed up. Moreover, the second outstanding advantage of the BT protocol is that it offers much greater redundancy because it eliminates the not-so-negligible unfortunate possibility that the server will go offline for whatever reason. The transfer speed can also reach extreme peaks because of the dynamic bandwidth allocation on all of the clients. Recently the BitTorrent protocol was enhanced with DHTs, which are Distributed Hash Tables. Thanks to its distributed systems nature, it allows users to connect and continue transferring data even with the absence of a dedicated tracker. It was a huge step toward decentralization, scalability, and fault tolerance. Lately, DHT has gained prestige. Companies such as Blizzard (World of Warcraft) and Valve (Steam) adopted this protocol as their main distribution method in order to deliver updates, patches, and so forth. It isn't uncommon at all to find various Linux distributions downloadable via BT protocols. Azureus The bundled feature list is really impressive. It allows multiple torrent downloads, upload and download speed limitation (globally or per torrent), configuring advanced seeding rules, and adjusting disk cache. It supports fast resume, can use proxies, its interface is highly customizable, and of course, we cannot forget about DHT support. It also uses only one port for all of the torrents, and includes an IRC plug-in to ask for help with ease.
Azureus is a Java-based, cross-platform freeware BitTorrent client licensed under the GNU GPL. It is one of the oldest clients (2003) and according to the SourceForge statistics, also the most popular, having been downloaded 156,825,483 times at the time of writing this article. It's recognized as the most stable and feature-laden client.
The latest stable release of Azureus at the time of writing is 3.0.3.4. Starting from version 3, Azureus redefined the way they approach P2P file-sharing, launching a new platform called Vuze Platform. Vuze is a media sharing application that acts just like YouTube, but is limited only to high-definition video content. Vuze also sells DRM-protected content.
Moreover, since Azureus 3.0, the user has been required to accept a modified version of the GNU GPL license prior to using the application. That also includes the Vuze-license and prohibitions for people under the age of 18. This is because Vuze sports a graphic browser as a main interface, where mature content may be presented.
All in all, Azureus is a very stable BT client that's jam-packed with dozens of features. It sports unique functions, such as the Vuze platform, and incorporates its very own DHT support, which is incompatible with the original BitTorrent release. Due to its Java nature, it is very resource intensive and some people find that it "eats up" their RAM. You also need a fairly powerful CPU. If your rig is antique, forget about Azureus.
Azureus mostly benefits those avid BitTorrent users that are truly going to use some of its outstanding functions and are willing to spare enough system resources. For the casual user that does not want to be heavily involved in the "inner structures" of the BT protocol, then Azureus may be overkill. Critics say Azureus is trying to reinvent the wheel. Anyway, try it out and see for yourself.
Summing up, we hand Azureus 8 points out of 10. We subtracted one for its performance and resource clogging, but unfortunately that's what developers need to put up with when working with Java in specific cases. Likewise, another point is lost due to its high level of complexity. Its design is by no means intuitive.
uTorrent is a freeware, Windows-only proprietary BitTorrent client. It is also called microTorrent thanks to the Greek μ letter prefix. It is considered the most lightweight, compact, and efficient peer-to-peer BT client. At the time of writing, the latest stable version is 1.7.5, and its size is 214kB. It was totally coded in C++ using custom-coded libraries and then compressed with UPX (.exe packer) to reduce its size.
It was already gaining recognition from the first days of its launch. Some of the most obvious reasons for that are its reduced size and the fact that it doesn't require installation. Because of this, it's extremely portable and resource efficient. Isn't it impressive that the client is able to run on a Win95 system with 486 processor and 14MB RAM? It was designed to showcase most of the functionalities offered by other standalone clients, such as Azureus and BitComet, while using minimal resources. It's been months since uTorrent received top ratings in all kinds of reviews, considering its performance, stability, built-in set of features, and support for antique hardware. It sports de facto standard functions, like multiple simultaneous downloads, configurable bandwidth scheduler, speed limiting (global or per-torrent), quick resumes, mainline DHT (compatible with BitTorrent DHT; trackerless support), HTTPS tracker support, customizable GUI (skins, etc.), embedded tracker, supporting proxies, protocol encryption (PE), configurable disk cache, and RSS support. On December 7, 2006 uTorrent was acquired by BitTorrent, Inc. This means that they have implemented most of uTorrent's code in their own BitTorrent client, which was basically the first client developed by CEO Bram Cohen himself. As a result, the latest version of BitTorrent is in fact a re-branded version of uTorrent. All in all, uTorrent deserves a 10/10 rating. In short we highly recommend trying out uTorrent as a BitTorrent client for people from all walks of life. It offers satisfying performance and feature-laden-ness for everybody from Joes and Jeffs, up to die hard Torrent fR3aK f4NaT1Ks (over-enthusiasts). Final Thoughts In this article we reviewed two of the most popular BitTorrent clients. We started this article with a brief overview of the BitTorrent protocol. By now you should be familiar with the necessary terminology and feel able to join in. Furthermore, we're sure that you have already decided which of the presented BitTorrent clients you are going to choose. Needless to say, there are dozens of other alternatives. Should you prefer a larger variety of software, then check out BitComet, the original BitTorrent client, Shareaza, and perhaps Rufus. Also, we shouldn't forget about the built-in torrent client for Opera browser. You may want to see how it works. Now that you're well prepared, you might want to immerse yourself in the BitTorrent community. It's a community built up by more than 150 million users. You are going to be blown away by the amazing speed of transfers, because depending on the situation, you may very easily reach your bandwidth peaks.
Summing up, uTorrent satisfies the "feature-rich and graphically empowered" guideline considering its level of performance, stability, effectiveness, and features. It's also impressive that all of the modern and powerful features are presented in a very understandable way so that they don't create confusion for those people that aren't familiar with the BitTorrent protocol systematization.
