GUID

GUID stands for globally unique identifier. It is a 128-bit value used to uniquely identify information in computer systems. GUIDs are designed to be unique across space and time, so identifiers created in different places do not collide. The term GUID is most common in Microsoft environments, while the broader, standards-based term UUID (Universally Unique Identifier) is defined by the UUID standard and is functionally equivalent.

A GUID is usually written as 32 hexadecimal digits in five groups separated by hyphens, in the form 8-4-4-4-12 (for example, 550e8400-e29b-41d4-a716-446655440000). Some representations include braces or a URN form such as urn:uuid:550e8400-e29b-41d4-a716-446655440000. Internally, a GUID contains fields that indicate its version and variant, which determine how the value was generated.

Generation methods vary by version. Version 1 is time-based and incorporates a timestamp and, often, the network address of the generating node. Version 3 and Version 5 are name-based, deriving the value from a namespace identifier and a name using MD5 (v3) or SHA-1 (v5). Version 4 is largely random and is widely used when a random or unpredictable identifier is desired. UUIDs are standardized by RFC 4122; GUIDs on Windows typically follow similar formats and can adopt these generation methods.

Common uses include keys for database records, identifiers for files and COM interfaces, and objects in distributed systems. The 128-bit size makes collisions extremely unlikely in practice, though GUIDs are not guaranteed to be cryptographically random or secure by themselves.