Windows – what purpose does HKCU\software\microsoft\windows\currentversion\explorer\fileexts serve

file-typeswindowswindows-registry

Back in the day, one merely need look at HKCR\.ext which would point to HKCR\type-handler.

HKCR is now a dynamic link to both HKCU\software\classes and HKLM\software\classes, in a cascade pattern (local user first, then local machine).

However, now we also have this ..\explorer\FileExts registry tree, presumably at both user and machine levels as well. What does this additional complexity provide?

I don't know about you, but I am forever fighting Windows to correctly open my files, with Explorer hanging quite often, or failing to open a given file from explorer. And it seems quite arbitrary, where an install of say TextPad on one machine will appear to be 100% functional, whereas on another will result in only limited functionality with either Explorer or TextPad crashing when a file is attempted to be opened (say via the right click menu, or send-to, or drag & drop, or double click).

I've asked a few times and done myriad searches, and I have yet to find a comprehensive "this is what all keys related to file types are and do, and how Microsoft intends that they be used for coherent cooperation and proper function of a users system."

Does anyone know where I might find a comprehensive 'best-practices' guide or exhaustive documentation for file-type-associations under windows?

Best Answer

  • I think the "best practice" is to use the bundled "Default Programs" setting with Windows, or a third-party tool like FileTypesMan or ASHociation. FileTypesMan also includes a command-line interface, appropriate for using it on client computers remotely (if need be).


    Explorer or TextPad crashing when a file is attempted to be opened (say via the right click menu, or send-to, or drag & drop, or double click).

    The application shouldn't crash if the association wasn't set up correctly, as the application wouldn't automatically open to begin with. It seems like there's another underlying issue with your operating system configuration, or the TextPad application itself.


    "this is what all keys related to file types are and do, and how Microsoft intends that they be used for coherent cooperation and proper function of a users system."

    It's unlikely you'll find any resources detailing a very low-level registry setting for a complex closed-source operating system, unless Microsoft has publicly released the information (or a third party has reverse-engineered its purpose). It's rare that Microsoft ever recommends the end user modify registry data outside of software development, precisely for this reason. If there is any information, you're likely to find it in the Microsoft Support Knowledge Base.

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