-ServerMessageBlock ( [SMB]) is a client/server protocol similar to remote procedure calls ([RPC]), but specialised for file system access. It was developed by [Intel], [Microsoft], and [IBM] in the early 1980s, and also had input from [Xerox] and [3Com]. It is the native method of file and print sharing for [Microsoft]'s operating systems, where it is called [Microsoft] Networking, but it is also used by [OS/2], Lan Manager and Banyan Vines. [Windows] for Workgroups, [Windows] 95, and [WindowsNT] all include [SMB] clients and servers. [SMB] originally ran on top of the lower level protocols NetBEUI and NetBIOS, but now typically runs over [TCP/IP]. 

-There are [SMB] servers and clients for Unix, as well. The most popular one is a reverse-engineered OpenSource implementation of the protocol called [Samba]. It allows Unix machines integrate networks consisting of Windows clients. [Samba] can even act as a "domain controller", removing the need for expensive [Windows] server licences. 

-While it is mainly used for file and printer sharing between computers, it has provisions for much more. [SMB] is a presentation layer protocol structured as a large set of commands (called "Server Message Blocks", hence the name). Clients and servers may implement different versions ("dialects") of the protocol, and will negotiate the version to use before starting a session. There are commands to support sharing of files, printers, serial ports, for user authentication, resource browsing, communications abstractions such as named pipes and mail slots, and other miscellaneous functions. A redirector packages [SMB] requests into a network control block (NBC) structure that can be sent across the network to a remote device. 

-[Microsoft] have extended [SMB] into [CIFS], slated as a replacement of the protocol for the InterNet which runs only runs over [TCP/IP].