Peer-to-peer file sharing

Peer-to-peer file sharing is the distribution and sharing of digital media using peer-to-peer (P2P) networking technology. P2P file sharing allows users to access media files such as books, music, movies, and games using a P2P software program that searches for other connected computers on a P2P network to locate the desired content. The nodes (peers) of such networks are end-user computers and distribution servers (not required).

The early days of file-sharing were done predominantly by client-server transfers from web pages, FTP and IRC before Napster popularised a Windows application that allowed users to both upload and download with a freemium style service. Record companies and artists called for its shutdown and FBI raids followed. Napster had been incredibly popular at its peak, spawning a grass-roots movement following from the mixtape scene of the 80's and left a significant gap in music availability with its followers. After much discussion on forums and in chat rooms, it was decided that Napster had been vulnerable due to its reliance on centralised servers and their physical location and thus competing groups raced to build a decentralised peer-to-peer system.

Peer-to-peer file sharing technology has evolved through several design stages from the early networks like Gnutella, which popularized the technology in several iterations that used various front ends such as Kazaa, LimeWire and WinMX before Edonkey then on to later models like the BitTorrent protocol. Microsoft uses it for Update distribution (Windows 10) and online video games use it as their content distribution network for downloading large amounts of data without incurring the dramatic costs for bandwidth inherent when providing just a single source.

Several factors contributed to the widespread adoption and facilitation of peer-to-peer file sharing. These included increasing Internet bandwidth, the widespread digitization of physical media, and the increasing capabilities of residential personal computers. Users are able to transfer one or more files from one computer to another across the Internet through various file transfer systems and other file-sharing networks.

The central index server indexed the users and their shared content. When someone searched for a file, the server searched all available copies of that file and presented them to the user. The files would be transferred directly between private computers (peers/nodes). A limitation was that only music files could be shared. Because this process occurred on a central server, however, Napster was held liable for copyright infringement and shut down in July 2001. It later reopened as a pay service.

After Napster was shut down, peer-to-peer services were invented such as Gnutella and Kazaa. These services also allowed users to download files other than music, such as movies and games.

Napster and eDonkey2000 both used a central server-based model. These systems relied on the operation of the respective central servers, and thus were susceptible to centralized shutdown. Their demise led to the rise of networks like Limewire, Kazaa, Morpheus, Gnutella, and Gnutella2, which are able to operate without any central servers, eliminating the central vulnerability by connecting users remotely to each other. However, these networks still relied on specific, centrally distributed client programs, so they could be crippled by taking legal action against a sufficiently large number of publishers of the client programs. Sharman Networks, the publisher of Kazaa, has been inactive since 2006. StreamCast Networks, the publisher of Morpheus, shut down on April 22, 2008. Limewire LLC was shut down in late 2010 or early 2011. This cleared the way for the dominance of the Bittorrent protocol, which differs from its predecessors in two major ways. The first is that no individual, group, or company owns the protocol or the terms "Torrent" or "Bittorrent", meaning that anyone can write and distribute client software that works with the network. The second is that Bittorrent clients have no search functionality of their own. Instead, users must rely on third-party websites like Isohunt or The Pirate Bay to find "torrent" files, which function like maps that tell the client how to find and download the files that the user actually wants. These two characteristics combined offer a level of decentralization that makes Bittorrent practically impossible to shut down. File-sharing networks are sometimes organized into three "generations" based on these different levels of decentralization. Darknets, including networks like Freenet, are sometimes considered to be third-generation file-sharing networks.

Peer-to-peer file sharing is also efficient in terms of cost. The system administration overhead is smaller because the user is the provider and usually the provider is the administrator as well. Hence each network can be monitored by the users themselves. At the same time, large servers sometimes require more storage and this increases the cost since the storage has to be rented or bought exclusively for a server. However, usually peer-to-peer file sharing does not require a dedicated server.