GUIDsUUIDs

GUIDs and UUIDs refer to 128-bit identifiers used to uniquely identify information in computer systems. GUID stands for Globally Unique Identifier and is the term commonly used by Microsoft, while UUID stands for Universally Unique Identifier and comes from the IETF standard that defines the concept. In practice, GUIDs and UUIDs denote the same kind of value and are intended to be unique across space and time.

A UUID is typically represented as 32 hexadecimal digits displayed in five groups separated by hyphens, in the form 8-4-4-4-12. This textual representation is commonly written in lowercase and may be shown with surrounding braces in some contexts. The 16-byte (128-bit) value can also be stored in binary form for efficient use in databases and network protocols.

The IETF RFC 4122 specifies several UUID versions. Version 1 is time-based and may incorporate the node’s MAC address. Version 3 and version 5 are name-based, using MD5 and SHA-1 respectively on a namespace and a name. Version 4 is generated randomly and is the most widely used due to its simplicity and anonymity. Some systems also support version 2, though it is less common in modern software.

Generation and usage vary by platform. Libraries typically provide functions to create UUIDs (for example, randomUUID or UUIDv4). UUIDs are often used as primary keys, identifiers for distributed resources, or as stable references in data merging. They can be stored in text form or in a 16-byte binary format, with some databases offering native UUID types to optimize indexing. Care should be taken with UUIDv1 as it may reveal timestamps and hardware addresses, raising privacy considerations; UUIDv4 is generally preferred when privacy is a concern.