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Session Manager Subsystem, or smss.exe, is a component of the Microsoft Windows NT operating system and successor operating systems. It is executed during the startup process of Windows NT, Windows 2000, XP, Server 2003 and Vista. At this time it:

  • Creates environment variables.
  • Starts the kernel and user modes of the Win32 subsystem. This subsystem includes win32k.sys (kernel-mode), winsrv.dll (user-mode), and csrss.exe (user-mode)[1]. Any other subsystems listed in the Required value of the HKLM\System\CurrentControlSet\Control\Session Manager\SubSystems Registry key are also started.
  • Creates DOS device mappings (e.g. COM1, LPT1, AUX, NUL, CON, and drive letters) listed at the HKLM\System\CurrentControlSet\Control\Session Manager\DOS Devices registry key. This can be used to create permanent subst drives.
  • Creates virtual memory paging files.
  • Starts winlogon.exe, the Windows logon manager.[2]

After the boot process is finished, the program resides in memory and can be seen running in the Windows Task Manager. It then waits for either winlogon.exe or csrss.exe to end. If things occur "normally", Windows is shut down. If the processes do not end in an expected fashion, smss.exe may hang the system.[2]


See also



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