What's Windows CLSID? Second Life UUID?

By Xah Lee. Date:

You know how on Windows you see this strings like this {838f9f38-f241-11de-a663-002421597a5c}? For example, on my PC, i have these mysterious files generated by Windows Vista right in my home directory:


And in my Event Viewer (Control Panel\Administrative Tools\Event Viewer or %SystemRoot%\system32\eventvwr.msc /s), for example there's a message:

The application-specific permission settings do not grant Local Launch permission for the COM Server application with CLSID {C97FCC79-E628-407D-AE68-A06AD6D8B4D1} to the user NT AUTHORITY\SYSTEM SID (S-1-5-18) from address LocalHost (Using LRPC). This security permission can be modified using the Component Services administrative tool.

What are those long strings?

CLSID = Globally Unique Identifier

That string is basically just a ID string. It is long because it is meant to be unique, to the degree that a randomly generated string will unlikely to be the same.

It is 32 digits of hexadecimal. So, the total possible such string is 16^32, which is 340282366920938463463374607431768211456 or approximately 10^39. Here's a example:

It is written in blocks separated by hyphen, then enclosed by curly brackets.

 12345678 1234 1234 1234 123456789012
 8        4    4    4    12

Here's a quote from Wikipedia Globally unique identifier:

Microsoft Windows uses GUIDs internally to identify the classes and interfaces of COM objects. A script can activate a specific class or object without having to know the name or location of the dynamic linked library that contains it.

Quote from Microsoft 2.5.5 Globally Unique Identifiers (GUIDs) @ http://msdn.microsoft.com/en-us/library/cc246025%28v=PROT.13%29.aspx:

In Microsoft Windows® programming and in Windows operating systems, a globally unique identifier (GUID), as specified in [RFC4122], is a 128-bit value that is a binary unique identifier (ID) for a specific entity. The term universally unique identifier (UUID) is sometimes used in Windows protocol specifications as a synonym for GUID.

CLSID = UUID = Universally Unique Identifier

Microsoft CLSID is just a different name for the scheme known as UUID (Universally Unique Identifier). The essence is that it's just a sequence of 32 hexadecimal digits, generated randomly, used to assign a ID to items.

It's used in Second Life too. In Second Life, every “agent” (that is, every account in Second Life), has a UUID, and every item you see in Second Life has a UUID (For example, images (aka textures), objects (prims), sounds, animation files). For example, here's a LSL code excerpt:

key pSprite = "1f9e3064-47e1-87bd-1b82-20638ae6e36e"; // particle image.

updateParticle() {
    // make particle, with burstrate and sprite age depending on avatar speed
    float speed = llVecMag(llGetVel());
    if (speed < 1.) {
        bRate = 1.;
        pAge = 1.2;
    } else {
        bRate = distBetweenCrumb/speed;
        pAge = trailLength / speed;
    partyOn ( pPtrn, beginColor, endColor, bRate, pAge, (key)pSprite, startScale, endScale, changeOrientationQ );

See also: Math: ID System, Number Base vs Number of Digits.