Universally Unique Identifier

A universally unique identifier (UUID) is a 128-bit number used to identify information in computer systems. Microsoft uses the term globally unique identifier (GUID), either as a synonym for UUID or to refer to a particular UUID variant.

When generated according to the standard methods, UUIDs are for practical purposes unique, without depending for their uniqueness on a central registration authority or coordination between the parties generating them, unlike most other numbering schemes. While the probability that a UUID will be duplicated is not zero, it is so close to zero as to be negligible.

Thus, anyone can create a UUID and use it to identify something with near certainty that the identifier does not duplicate one that has already been, or will be, created to identify something else. Information labeled with UUIDs by independent parties can therefore be later combined into a single database, or transmitted on the same channel, without needing to resolve conflicts between identifiers.

Adoption of UUIDs and GUIDs is widespread, with many computing platforms providing support for generating them, and for parsing their textual representation.

UUIDs were originally used in the Apollo Network Computing System (NCS) and later in the Open Software Foundation's (OSF) Distributed Computing Environment (DCE). The initial design of DCE UUIDs was based on the NCS UUIDs, whose design was in turn inspired by the (64-bit) unique identifiers defined and used pervasively in Domain/OS, an operating system also designed by Apollo Computer. Later, the Microsoft Windows platforms adopted the DCE design as globally unique identifiers (GUIDs). RFC 4122 registered a URN namespace for UUIDs, and recapitulated the earlier specifications, with the same technical content. By the time RFC 4122 was published as a proposed IETF standard, the ITU had also standardized UUIDs, based on the previous standards and early versions of RFC 4122.

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