The recommendation that BiaB and RealBand are placed in the root directory has been around for many, many years.

Microsoft made recommendations to no longer use "Program Files" or "Program Files (x86)" around the time of Windows 7. This was mainly related to security and access issues to the new protection systems in Windows 7 onwards.

The recommendation is definitely to use the root of the selected drive. Has been for a long time.

I may be wrong, but I don't think that RealBand has a single association with .SEQ files, the way BiaB does for SGU, MGU etc. The list, which may contain one of more associations, is defined in the registry in:
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.seq\OpenWithList






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