Session Management Subsystem

Session Manager Subsystem, or smss.exe, is a component of the Microsoft Windows NT family of operating systems, starting in Windows NT 3.1. It is executed during the startup process of those operating systems. 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). 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. CON:, NUL:, AUX:, COM1:, COM2:, COM3:, COM4:, PRN:, LPT1:, LPT2:, LPT3:, 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.

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</tt> to end else Windows will shut down. If the processes do not end in an expected fashion, smss.exe</tt> may hang the system.