This subkey contains entries that define the system directories for the Win32 subsystem (32-bit Windows) under this path:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Windows
Directory REG_EXPAND_SZ Directory name
Defines the directory for Windows NT.
Default: %SystemRoot%
SystemDirectory REG_EXPAND_SZ Directory name
Defines the directory for the Windows NT system files.
Default: %SystemRoot%\system32
The Registry entries for starting the Win32 subsystem are defined under the Required and Windows value entries in the Session Manager\Subsystem subkey, as described earlier in this section.