Network File System (NFS) is a protocol originally developed by Sun Microsystems in 1984 and defined in RFCs 1094, 1813, (3010) and 3530, as a file system which allows a computer to access files over a network as easily as if they were on its local disks.
Version 2 of the protocol originally operated entirely over UDP and was meant to keep the protocol stateless, with locking (for example) implemented outside of the core protocol.
Version 3 introduced support for using TCP as transport. Several vendors had already extended NFSv2 to support TCP as transport. Using TCP as transport made using NFS over a WAN more feasible (although not necessarily practical).
Version 4, influenced by AFS, includes performance improvements, mandates strong security, and introduces a stateful protocol.
NFS is strongly associated with UNIX systems, though it can be used on any platform such as Macintosh and Microsoft Windows operating systems. The server message block (SMB), a similar protocol, is the equivalent implementation of a network file system under Microsoft Windows.
The term "network file system" is also often used as a generic term — see file system for other examples.
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