File sharing in its current form began with the creation of the peer-to-peer (P2P) client Napster in the late 90's. Through P2P software, peers can send and receive files - most commonly media files, such as music and movies. The concept relies on the peers ability to 'share' files, as without peers making their files available, there would be no content available for download.
Napster had a monopoly of the file sharing market until its demise early in the next decade. After several high profile lawsuits, such as those from artists Metallica, Dr Dre and Madonna, Napster was forced to close down its service and declared itself bankrupt in 2002. Despite its closure, Napster's legacy still lives on today. Napster paved the way for many other decentralised file sharing programs such as Kazaa, WinMX, Limewire and Bearshare.
From 2002 to mid 2005, Kazaa and WinMX became the most widely used P2P software on the market. Throughout its existence, Kazaa has been plagued by the inclusion of malware in its software which led many people to switch to the malware-free WinMX software. One study indicated WinMX reached its peak in 2005 as the worlds most widely used P2P software, with an estimated 2.1 million concurrent users. Kazaa had many legal challenges through its tenure, with the Australian Recording Industy Association (ARIA) and the Recording Industry Association of America (RIAA) both launching campaigns against the company behind Kazaa, Sharman Networks, and many individual Kazaa users taken to court for their role in the distribution of files under copywrite. WinMX, due to its Canadian based, managed to fly beneath the radar for a lot longer than many were expecting - even to this day it is not known of any WinMX users being taken to court for sharing files - but in September 2005 the RIAA sent the WinMX owners, Frontcode Technology, a cease and desist letter, causing the network to be taken offline a week later.
While Kazaa has all but dropped of the radar, WinMX still lives on due to its large Opennap community and an enthusiastic userbase which created their own patches and cache servers to ensure the networks continued existence.
Since the official demise and WinMX and the failure of Kazaa's legal download service, open source P2P client Limewire has gained significant popularity. While the various recording industry associations around the world will likely try and force the closure of Limewire like many other P2P clients before it, Limewire's open source nature will protect it from any quick closure attempt.
The traditional P2P client, based on the Napster model, is now losing ground to what many people consider to now be the preferred method of transferring files - BitTorrent. The BitTorrent protocol does work on a send and receive model, but the method of downloading files differs significantly. A user must first search the internet through the HTTP protocol for the file of their choice. Torrent files, containing the necessary information to initiate a download, are found on BitTorrent trackers, scattered over the internet. When a user downloads the torrent file, their BitTorrent client will open and the file will begin downloading in pieces. The file may not necessarily download sequentially, rather, it will download in pieces that are most readily available. Downloads are more often than not multi-sourced, which allows the potential for great speeds.
BitTorrent also appears to be the future of file sharing. As new trackers are appearing consistently, the recording associations on recourse is to shut down popular trackers - which are quickly replaced. The software is also used for many legal purposes, such as downloading free games and podcasts, which should see BitTorrent's existence stay secure for the foreseeable future.