GUID or UUID (globally unique identifier) is a unique reference number used as an identifier in computer software.
GUIDs are usually stored as 128-bit values, and are commonly displayed as 32 hexadecimal digits with groups separated by hyphens, such as:
- Microsoft Windows uses GUIDs internally to identify the classes and interfaces of COM objects. A script can activate a specific class or object without having to know the name or location of the dynamic linked library that contains it. Because of this, ActiveX, a system for downloading and installing controls in a web browser, uses GUIDs to uniquely identify each control.
- Intel's GUID Partition Table, or GPT, a system for partitioning hard drives.
JT files use a partitioning into 4+2+2+8*1 bytes to represent nodes in the data structure and segment IDs.
Second Life uses GUIDs for identification of all assets in its world.
- Database developers and administrators may use GUIDs as primary keys for database tables to ensure uniqueness between database servers, at the cost of making the working set size for caching much larger for a relational database server, potentially impacting application performance.