What is the Universal Naming Convention (UNC)?
The Universal Naming Convention (UNC) is a standard for naming resources -- such as files and devices -- that are shared by computers on a network.
This standard was originally used by systems running Microsoft operating systems (OSes) and those that needed to share network resources with Microsoft platforms on a local area network. An analogous standard for Unix and Linux systems pre-dates UNC and was designed as an extension of pathnames. Modern Microsoft systems can interpret Unix and Linux pathnames as UNC strings.
UNC was first used on OS/2, an OS designed by Microsoft and IBM. Another term often used for the same concept and using the same abbreviation is Uniform Naming Convention.
The term universal makes the distinction between global and local names. Universal names are interpreted globally; local names are interpreted in a local context. The term uniform is used to emphasize that the same naming convention is used regardless of the type of resource it refers to.
How do you use the Universal Naming Convention?
In Microsoft Windows, a name is specified in a UNC string and adheres to the following format:
\\<server name>\<share point>\<path to resource>
- <server name> refers to the device that holds the resource.
- <share point> refers to the shared data area.
- <path to resource> is the logical directory where the requested information can be found, along with the name of the resource.
In Unix and Linux systems, UNC strings are specified in a slightly different way -- forward slashes are used instead of backslashes.
- <hostname> refers to the device that holds the resource.
- <pathname> refers to the logical directory where the resource can be found, along with the name of the resource. The <pathname> can be pre-fixed with <share point> when the resource is on a Microsoft platform.
History of the Universal Naming Convention
The idea of a standard way of referencing a resource on another computer dates back to at least March 1974, when it was the subject of RFC 615 "Proposed Network Standard Data Pathname syntax." A decade later, the idea was an integral part of engineering workstations, including Apollo Computer Inc., which was later acquired by Hewlett Packard, and Sun, which was later acquired by Oracle Corp. The idea is examined in Chapter 1 of the Domain System User's Guide, which discusses the Unix-like OS for Apollo computers.
The term Universal Naming Convention appears in patent US5363487A, filed by Microsoft in August 1989, and in patent US534199A, filed by IBM in April 1992. In both patents, example use cases mention OS/2, the OS that began as a joint project between Microsoft and IBM. The IBM patent specifically names IBM and Microsoft as co-inventers of the Universal Naming Convention -- and states that other companies, such as Novell, which was later acquired by Micro Focus, implement UNC in their products so third-party DOS and OS/2 applications can request services from their servers.
By 1995, UNC was a native feature of both Windows NT and Windows 95.
Alternatives to UNC
Windows Explorer, the Windows Command Prompt or Windows PowerShell can be used instead of a UNC path to map network drives and access folders on a computer remotely using a drive letter instead of a UNC path.
Learn what UNC path injection is and how a now-patched vulnerability in the Zoom Windows client could have exposed user credentials.