What is Globally Unique Identifier (GUID)?
A globally unique identifier (GUID) is a 128-bit number created by the Windows operating system or other Windows application to uniquely identify certain components, hardware, software, files, user accounts, database entries, and other elements.
GUIDs are part of the Universal Unique ID (UUID) standard used in Windows and Windows applications.
GUIDs were originally designed to keep track of instances of Component Object Model (COM) objects and are still used to identify COM DLLs in the Windows registry.
GUIDs were created with an algorithm that used the user's MAC (Media Access Control) address. This system was later deleted because users were concerned that documents could be traced back to individual computers. GUIDs can now be created in a number of ways with a combination of unique settings.