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GUID Meaning & Definition

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. 

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. 










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