(1) A network of computers configured to allow certain files and folders to be shared with everyone or with selected users. Peer-to-peer networks are quite common in small offices that do not use a dedicated file server. All client versions of Windows, Mac and Linux can function as nodes in a peer-to-peer network and allow their files to be shared.

Files and folders can be configured to allow network users to copy them, but not alter them in their original location, which is a common safety precaution. However, files and folders can also be assigned a "read/write" status that allows either selected users or all users on the network to change them. See share. See also grid computing.

(2) Using the Internet as the world's largest file sharing network. Originally for music files, and subsequently for videos, this type of sharing was popularized by the famous Napster service as well as Gnutella (www.gnutella.com), Grokster (www.grokster.com), KaZaA (www.kazaa.com) and others. Users upload copyrighted songs to a central server, a group of servers or to selected user computers, and people download the files that are available. Almost every song ever recorded has been uploaded to some music sharing venue.

In 2003, Napster was resurrected into a legitimate service competing with other online music stores such as iTunes (www.itunes.com) and Yahoo! Music Jukebox (formerly MusicMatch) (www.musicmatch.com). Although Apple legally sold more than a billion songs from its iTunes music service in 2006, it was estimated that more than 15 billion copyrighted songs were illegally shared or downloaded from Web sites in that same year.

File sharing systems are architected in different ways as outlined in the following illustrations. See Napster, KaZaA, BitTorrent and P2P TV.