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    By Vangie Beal

    What is a GUID?

    A Globally Unique Identifier (GUID) is a unique ID that is computed by Windows and Windows applications. It’s a 128-bit number used to identify user accounts, documents, software, hardware, database entries, sessions, and other items. For example, a website may generate a GUID and assign it to a user’s browser to record and track the session.

    GUID may also be referred to as a Universally Unique Identifier (UUID). The two terms are synonymous. GUIDs can be used for:

    • Setting a unique primary key in databases
    • Setting a unique filename for uploaded files
    • Setting a unique name for resources
    • Creating and registering unique IDs without contacting a central authority

    A GUID follows a specific structure defined in RFC 4122 and comes in multiple formats. However, all variants follows the same structure:

    xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx

    M represents the version. N represents the variant.

    What are the types of GUIDs?

    The general types of GUIDs include:

    • Random: Uses a system to generate a random, 128-bit number
    • Time-based: Creates a GUID based on the current time
    • Hardware-based: Makes a GUID with certain portions based on hardware features, such as the MAC address of a network card.
    • Content-based (MD5 or SHA-1 hash of data): Creates a GUID based on a hash of the file contents. Files with the same contents will be assigned the same GUID.

    Creating a GUID

    To create a GUID, there are a multitude of online GUID generators, such as guidgenerator.com. In addition, there are also GUID libraries for programming languages such as PHP, Ruby, and Python.