RegFree COM (or Registration-Free COM) is a technology introduced with Windows XP that allows Component Object Model (COM) components to store activation metadata and CLSID (Class ID) for the component without using the registry. Instead, the metadata and CLSIDs of the classes implemented in the component are declared in an assembly manifest (described using XML), stored either as a resource in the executable or as a separate file installed with the component. This allows multiple versions of the same component to be installed in different directories, described by their own manifests, as well as XCOPY deployment. This technique has limited support for EXE COM servers and cannot be used for system-wide components such as MDAC, MSXML, DirectX or Internet Explorer.
During application loading, the Windows loader searches for the manifest. If it is present, the loader adds information from it to the activation context When the COM class factory tries to instantiate a class, the activation context is first checked to see if an implementation for the CLSID can be found. Only if the lookup fails is the registry scanned.
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