GUIDs

A GUID stands for Globally Unique Identifier and is a 128-bit value used to identify information in computer systems. GUIDs are designed to be unique across space and time, allowing objects created on different machines to be identified without a central coordinating authority. They are conceptually the same as UUIDs defined by international standards.

Most commonly represented as a 36-character string consisting of five groups separated by hyphens in the form 8-4-4-4-12, using hexadecimal digits. In storage they can also be kept as 16 bytes of binary data; some databases store them as 36-character strings or as 32 hexadecimal digits without hyphens.

GUIDs are generated according to several schemes recognized in RFC 4122. Version 1 is time-based and may incorporate the computer’s network address. Version 3 and Version 5 are name-based, using MD5 or SHA-1 on a namespace and a name. Version 4 is random. Version 2, a DCE security variant, is rarely used.

They are used to identify records, components, or sessions in distributed systems, databases, APIs, and software installations. Because they are designed to be globally unique, GUIDs reduce the need for central ID authorities or coordination.

Privacy and performance considerations: Version 1 IDs can reveal creation time and hardware identifiers; Version 4 avoids this. Storing GUIDs as binary 16 bytes is efficient and speeds indexing, while textual forms (36-char strings) are easier to read but larger.

Standards and terminology: GUID is the Microsoft name for what RFC 4122 calls a UUID. Most programming languages and databases provide libraries to generate and manipulate GUIDs, and common database types include SQL Server’s uniqueidentifier and PostgreSQL’s uuid.