Posix
The value of
Posix is
%SystemRoot%\system32\psxss.exe, but this executable does not exist (at least not on my Windows box). This is apparently the case because
Windows originally supported the
POSIX and
OS/2 subsystems, which both are no longer provided.
Yet, with build 2016, Microsoft introduced the
Linux subsystem (beta), aka
WSL. It allows to run native
Ubuntu user mode console binaries in the
bash shell in Windows 10.
Required
The value in
Required lists the
subsystems that load when Windows
boots up (see also value of
Optional).
The items in this string are names of other values under this registry key.
These subsystems are started by
smss.exe (the
session manager).
On some machines (most?), the value is Debug Windows
Windows
The value of Windows might be something like
%SystemRoot%\system32\csrss.exe ObjectDirectory=\Windows SharedSection=1024,20480,768 Windows=On SubSystemType=Windows ServerDll=basesrv,1 ServerDll=winsrv:UserServerDllInitialization,3 ServerDll=winsrv:ConServerDllInitialization,2 ServerDll=sxssrv,4 ProfileControl=Off MaxRequestThreads=16