A GUID (Globally Unique Identifier) is a unique identifier used in software to uniquely identify resources. The probability of a GUID being duplicated is extremely low, although not impossible, especially if GUIDs are generated on systems with unsynchronized clocks or poor random number generators.
A GUID is typically generated using combinations of the current time, the MAC address of the machine generating the GUID, and a random number. This results in an identifier that is unique to the machine and the moment in time it is generated.
GUIDs are used in a variety of software applications, from assigning unique identifiers to objects in database systems to uniquely identifying transactions and messages in distributed systems.
GUIDs (Globally Unique Identifiers) have their origins in UUIDs (Universally Unique Identifiers), which were originally defined as part of the Apollo NCS (Network Computing System) software standard in 1989. Over time, they have become a standard way of generating unique identifiers in many software systems.
Although the terms GUID and UUID are often used interchangeably, there is a small difference between them. A GUID is a specific variant of a UUID. All GUIDs are UUIDs, but not all UUIDs are GUIDs. The main difference lies in how and where they are used, with GUIDs commonly used in Microsoft Windows and UUIDs in Unix and Unix-like systems.
GUIDs can be generated in various ways, each corresponding to a different version. For example, version 1 GUIDs are based on the current time and the MAC address of the computer, while version 4 GUIDs are based on random numbers. The choice of version to use depends on the specific requirements of the system in question.
GUIDs are useful in a variety of situations where a unique identifier is required. Some practical applications include identifying records in databases, identifying objects in software systems, and correlating events in distributed systems.