Both Diamond version 3 and version 4 have a user interface to POV-Ray (the Persistence of Vision Raytracer, cf. www.povray.org). While Diamond 3 expects POV-Ray version 3.6 to be installed, Diamond 4 expects POV-Ray version 3.7.
(Nevertheless you can run Diamond 4 with POV-Ray version 3.6 and Diamond 3 with version 3.7.)
A problem may arise that POV-Ray version 3.7 uses a different sub-folder structure in the "C:\Program Files" directory
on your computer than the precursor 3.6.
When trying to locate the POV-Ray's main executable, which is "pvengine.exe" (there is also a "pvengine64.exe" for 64-bit Windows available),
both Diamond version 3 and version 4 first check the path that pvengine.exe (or pvengine64.exe) writes into its Windows Registry section,
which is located under HKEY_CURRENT_USER\Software\POV-Ray\...
If this information is not available, Diamond tries to locate pvengine.exe (or pvengine64.exe on 64-bit Windows) in
the "C:\Program Files\..." folder.
The search for the POV-Ray engine fails, if neither the program POV-Ray has been executed at least one on your Windows PC
and it has been installed in a folder other than the default folder.
The easiest way is to execute POV-Ray at least once
from the Windows desktop (usually there should be a "POV-Ray v3.6" or "POV-Ray v3.7" icon on the desktop)
or from the Windows Start menu, so that pvengine.exe or pvengine64.exe, rsp., can write the path to its executable into the
Windows Registry (and Diamond can locate it later from there when you call a POV-Ray command).
Diamond Version 4 only
In Diamond version - but not Diamond version 3 - you receive the following message box, when it fails to locate the POV-Ray engine:
You have the choice to browse yourself for "pvengine.exe" or "pvengine64.exe", using the File Browse dialog:
When you confirm with OK, Diamond stores the path to the POV-Ray engine in its Windows Registry section for subsequent calls of POV-Ray commands.