Registry Clean Pro

A utility to fix errors and optimize the performance of the Windows registry.

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Registry Clean Pro - Glossary

COM/ActiveX objects

COM stands for Component Object Model. This technology allows applications to share and reuse common functionality. For example, DirectX is a set of COM objects used by computer games to play music and sounds, receive input from joysticks, and communicate with 3D graphics cards.

ActiveX objects (or "controls") are visual components used by software programs and web pages. ActiveX controls are implemented using the COM technology and can be automatically downloaded, installed and executed by a web browser. For example, Macromedia Flash player is actually an ActiveX control.

Content Type

In Microsoft Windows, the Content Type registry values are stored in file extension registry records in HKEY_CLASSES_ROOT and are used by Windows Internet Explorer to correctly handle files received from the Internet.

Content Type Registry Value

For example, the Content Type value for the .gif extension is defined in the registry as "image/gif". When Internet Explorer requests a .gif file from the Internet, this record causes it to display the .gif file in the Explorer window instead of asking you to save it to your hard drive.

File Extension Record

The file extension records are stored in the HKEY_CLASSES_ROOT registry key and are used to associate a particular file extension with an installed application. For example, a file with a .txt extension is usually associated with Notepad.

File extension records do not specify the associated application directly. Instead, they contain pointers to the corresponding file type records, which in turn point to the executable files of the associated applications. File extension records may also contain a Content Type value, which is used by Internet Explorer.

In the following example, the .txt file extension record points to the "txtfile" file type record:

File Extension Record

Multiple file extension records can point to the same file type record. This is used to associate several file extensions with the same application. For example, .8ba, .8bc, .8be, .8bf file extensions all point to the "Photoshop.Plugin" file type record and are handled by the same application, Adobe Photoshop:

Multiple File Extension Records

File Type Record

The file type records are stored in the HKEY_CLASSES_ROOT registry key and are used to specify name, default icon and shell commands for a particular file type. Each file type record is referred by one or more file extension records.

In the following example, the "txtfile" type has a default icon and includes Open, Print, and Print To commands:

File Type Record


GUID stands for Globally Unique Identifier. It is a 128-bit integer number that is guaranteed to be unique throughout the entire world. In Microsoft Windows, GUIDs are a key part of the COM programming model and are used as identifiers of COM objects and their interfaces. A GUID assigned to a COM object is called CLSID ("Class ID"). GUIDs are stored in the registry in the following format:



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