GUID's – Global Unique Identifiers

The Windows Registry introduces the user to a world of new terminology. In the previous article we encountered SID's. Now it is the turn of GUID's.

Just like SID's, GUID's are used extensively throughout the Registry. GUID’s are essentially a way to identify an object. However they also name that object uniquely so that no other object has the same GUID.

Now, these "objects" can be anything from an application, part of the operating system or a physical device like a graphics card to the actual computer itself.

Why do we need GUID's..?

Well it is a good idea to define every object on the computer with a unique identifier (GUID). This is because it is possible to have two objects on your computer that have the same "name." So by giving both these objects a unique identifier the computer can distinguish between them.

Both the Windows operating system and software applications that run on your computer, require EVERY object referenced in the Registry to have a unique identity.

Programmers use applications like GUIDGEN.EXE to create these special identifiers, whereas Windows creates them internally.

The GUID concept is based on the Universally Unique Identifiers (UUIDs) defined by the Open Software Foundation (OSF) as part of the Distributed Computing Environment (DCE) - but that is probably more than you wanted to know!

Just remember:..

No matter how many GUID's are created they are ALWAYS unique!

It might help to think of GUID's as similar to a Social Security number – your number is unique and it identifies you as you…

So what do GUID's look like?

Well they are what is called "hexadecimal" numbers - a human-friendly representation of binary coded values.

Essentially each GUID is made up of 5 groups of characters. Each group has a set (block) number of characters as follows: 8, 4, 4, 4, and 12. For example: B96073C9-0E9E-406F-B4A6-620E06242B20

Each one of these groups can be made up of characters that are: numbers 0 -9 and letters a – z. Fig 1.0 below shows an example of a GUID from the Registry. In this example the GUID is the data contained in the ServiceName value.

Fig 1.0  An Example of a GUID from the Registry

GUIDs are not unique to the Windows Registry. The online virtual world called Second Life (SL) uses GUIDs to track all the assets used in its virtual environment, and database servers can use GUIDs to create unique row identifiers.

That's all you really need to understand about GUIDs!

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