Explorer Replacement mode is controlled by the options on the Launching Opus / Explorer Replacement Preferences page. Selecting any option other than Don't replace Explorer activates Explorer replacement mode.

On Windows 10 and above, the Win+E is intercepted by a different process to Explorer Replacement, and can be set to open Opus even if replacement mode is disabled, from the Launching Opus / From the Win + E hotkey Preferences page.

When Explorer Replacement mode is enabled, it is still possible to get to File Explorer if desired:

• From the Start Menu, select Run (or push Win+R) and enter explorer.exe
• Right-click on any folder and choose Open in Explorer from the context menu
• Click the pinned Explorer icon on the taskbar

Even when Explorer replacement mode is enabled, there are some cases when Explorer will continue to open:

• Subject to the setting on the Launching Opus / Explorer Replacement page, a Lister may not open for all types of folder.
• A program that specifically invokes Explorer may not be able to be intercepted by Opus (although many times it will).
• Opus will never open the Control Panel (or its various sub-pages) - they will always open in Explorer.

Opus does not replace the desktop (which is actually implemented by explorer.exe), nor does it replace the standard File Open / Save dialogs in other applications.

Explorer Replacement requires changes to the Windows registry and so is generally unavailable when running a USB exported version of Directory Opus, however there is an option to temporarily make the registry changes needed (which might work, depending on your user permissions, or it might not).