The Common Internet File System (CIFS) is the standard way that computer users share files across corporate intranets and the Internet. An enhanced version of the Microsoft open, cross-platform Server Message Block (SMB) protocol, CIFS is a native file-sharing protocol in Windows 2000.  

CIFS defines a series of commands used to pass information between networked computers. The redirector packages requests meant for remote computers in a CIFS structure. CIFS can be sent over a network to remote devices. The redirector also uses CIFS to make requests to the protocol stack of the local computer. The CIFS messages can be broadly classified as follows: 

• Connection establishment messages consist of commands that start and end a redirector connection to a shared resource at the server.

• Namespace and File Manipulation messages are used by the redirector to gain access to files at the server and to read and write them.

• Printer messages are used by the redirector to send data to a print queue at a server and to get status information about the print queue.

• Miscellaneous messages are used by the redirector to write to mailslots and named pipes. 

Some of the platforms that CIFS supports are: 

• Microsoft Windows 2000, Microsoft® Windows NT®, Microsoft® Windows® 98, Microsoft® Windows® 95

• Microsoft® OS/2 LAN Manager

• Microsoft® Windows® for Workgroups

• UNIX

• VMS

• Macintosh

• IBM LAN Server

• DEC PATHWORKS

• Microsoft® LAN Manager for UNIX

• 3Com 3+Open

• MS-Net 

CIFS complements Hypertext Transfer Protocol (HTTP) while providing more sophisticated file sharing and file transfer than older protocols, such as FTP. CIFS is shown servicing a user request for data from a networked server in Figure B.17.

Definition sourced from http://technet.microsoft.com/en-us/library/cc939973.aspx., © 2014 Microsoft