Windows Registry Documentation

CLSID Keys (Class Identifiers)

CLSID keys are a fundamental part of the Windows registry, used to uniquely identify COM (Component Object Model) objects. Each CLSID is a GUID (Globally Unique Identifier) that serves as a pointer to the definition of a specific COM class, including its associated DLL or EXE, and its programmatic identifier (ProgID).

What is a CLSID?

A CLSID is a 128-bit integer that uniquely identifies a COM class. This ensures that even if multiple COM classes share similar names or functionalities, they can be distinguished. Windows uses CLSIDs to locate and instantiate COM objects requested by applications.

Location in the Registry

CLSID keys are primarily located under the following registry path:

HKEY_CLASSES_ROOT\CLSID

Each CLSID GUID is represented as a key under HKEY_CLASSES_ROOT\CLSID. The default value of this key is typically the programmatic identifier (ProgID) of the COM class, or a descriptive string.

Common Subkeys

Within a CLSID key, you'll find various subkeys that provide essential information about the COM object:

(Default) (Value)

Represents the programmatic identifier (ProgID) or a descriptive name for the COM class.

InprocServer32 (Key)

Specifies the path to the DLL that implements the COM object for in-process activation (i.e., the DLL runs within the same process as the client application). This key often contains a default value indicating the path to the DLL.

  • (Default) (Value): Path to the DLL.
  • ThreadingModel (Value): Indicates the threading model the COM server supports (e.g., "Apartment", "Free", "Both", "Neutral").

LocalServer32 (Key)

Specifies the path to the EXE that implements the COM object for out-of-process activation (i.e., the EXE runs in its own process). This key often contains a default value indicating the path to the executable.

  • (Default) (Value): Path to the executable.

ProgID (Key)

This key contains a default value that is the programmatic identifier associated with the CLSID. This is often a more human-readable name used by applications to refer to the COM object.

TypeLib (Key)

References the type library associated with the COM object, allowing applications to query its interfaces and methods.

  • (Default) (Value): The libid (library identifier) of the type library.

Example CLSID Entry

Below is a simplified representation of a CLSID entry in the registry:

HKEY_CLASSES_ROOT
└── CLSID
    └── {XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX}  <-- Your CLSID GUID
        ├── (Default) = "My COM Component"
        ├── InprocServer32
        │   ├── (Default) = "C:\Path\To\MyComponent.dll"
        │   └── ThreadingModel = "Apartment"
        ├── ProgID
        │   └── (Default) = "MyComponent.Object"
        └── TypeLib
            └── (Default) = "{YYYYYYYY-YYYY-YYYY-YYYY-YYYYYYYYYYYY}" <-- Type Library GUID

Importance and Usage

CLSIDs are crucial for Windows functionality, enabling the extensibility of the operating system and applications. They are used extensively by:

Understanding CLSID keys is essential for advanced Windows troubleshooting, development, and system administration, particularly when dealing with COM-based technologies.