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[Bree]

...Windows is just a User Interface, that sits on top of a Disk Operating System (DOS).

That's not entirely true. It was true for Win3.x/Win95/98 where DOS was the underlying OS that everything else ran on, but starting with Windows 2000 everything now sits on top of the Windows NT Kernel.

Architecture of Windows NT - Wikipedia

The Win32 subsystem runs in User Mode on top of that, and supports the Windows GUI. It also supports the use of NT Virtual DOS machines, which is what actually runs your DOS commands now.

The Windows NT 32-bit user-mode executable which forms the basis for a single DOS (or Windows 3.x) environment is called ntvdm.exe.

Virtual DOS machine - Wikipedia