For almost all practical purposes, UUID and GUID are the exact same thing. They are both 128-bit unique identifiers used to label data across distributed systems without needing a central authority.
The primary difference is terminology and ecosystem: UUID is an open standard defined by the IETF, while GUID is a term coined and popularized by Microsoft. Key Similarities and Differences UUID (Universally Unique Identifier) GUID (Globally Unique Identifier) Origin Standardized by the IETF (RFC 4122 / RFC 9562). Created and used primarily by Microsoft. Size 128 bits (16 bytes). 128 bits (16 bytes). Format
8-4-4-4-12 hex characters (e.g., 123e4567-e89b-12d3-a456-426614174000).
Identical format, but sometimes enclosed in curly braces {}. Ecosystem Web development, Linux, macOS, open-source databases. Windows OS, .NET frameworks, MS SQL Server. Byte Ordering Big-Endian (Network byte order). Mixed-Endian (Little-Endian for the first 3 components). Technical Distinctions
While they serve the same function, under-the-hood differences exist due to how they evolved:
The Microsoft Variant: A GUID is technically just one specific variant of a UUID. The official UUID specification reserves a specific “variant” bit pattern to signify that the ID was generated using legacy Microsoft GUID rules.
Byte Layout: When stored as raw binary data in memory, a standard UUID uses big-endian format. A Microsoft GUID uses mixed-endian format. This can cause data-shuffling quirks if you transfer raw binary IDs between a Windows system and a Linux system without proper parsing.
Versions: The UUID standard officially outlines several versions (like UUIDv1 for time-based, UUIDv4 for purely random, and UUIDv5 for name-based hashes). Microsoft GUID generation tools historically mapped to these same underlying structures (most modern GUIDs are equivalent to a UUIDv4). When to Use Each
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