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A universally unique identifier (UUID) is a 128-bit number that identifies unique Internet objects or data. A UUID is generated by an algorithm with values that are based on a machine's network address.
UUIDs are used by many software companies, such as Microsoft and Apple, and are extensively used as components of Microsoft’s globally unique identifiers (GUIDs). Other UUID uses include Linux’s ext2/ext3 file system.
The UUID was created in the Network Computing System (NCS), which later became a part of the Distributed Computing Environment (DCE) standardized by the Open Software Foundation (OSF).
A UUID is typically denoted by 32 hexadecimal digits displayed in five character groups individually separated by hyphens. For example, a UUID may appear as follows: f81d4fae-7dec-11d0-a765-00a0c91e6bf6.
Different mechanisms are used to generate UUIDs to determine and compare UUID uniqueness levels. Based on the type of mechanism used, the generated UUID will be either completely or practically different from other generated UUIDs. UUIDs are made up of combined components; therefore, some kind of uniqueness is always present in any generated UUID.
A guaranteed unique identifier includes a reference to the network address of the UUID generating host, a time stamp and an arbitrary component. Because network addresses for each computer vary, the time stamp is also different for each generated UUID. Thus, two different host machines exhibit sufficient levels of uniqueness. The randomly created arbitrary component is added for enhanced security.
UUIDs are also part of the Tmodel data structure, which is a service type in the Universal Description Discovery and Integration (UDDI) registry used for Web service discovery.