Session Manager Subsystem, or , is a component of the

Microsoft Microsoft Corporation is an American multinational corporation, multinational technology company, technology corporation producing Software, computer software, consumer electronics, personal computers, and related services headquartered at th ...

Windows NT Windows NT is a proprietary graphical operating system produced by Microsoft, the first version of which was released on July 27, 1993. It is a processor-independent, multiprocessing and multi-user operating system. The first version of Wi ...

family of

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ef ...

s, starting in

Windows NT 3.1 Windows NT 3.1 is the first major release of the Windows NT operating system developed by Microsoft, released on July 27, 1993. At the time of Windows NT's release, Microsoft's Windows 3.1 desktop environment had established brand recognition ...

. It is executed during the startup process of those operating systems (it is the first user-mode process started by the kernel), at which time it performs the following tasks: *Creates

environment variable An environment variable is a dynamic-named value that can affect the way running processes will behave on a computer. They are part of the environment in which a process runs. For example, a running process can query the value of the TEMP env ...

s. *Starts the

kernel Kernel may refer to: Computing * Kernel (operating system), the central component of most operating systems * Kernel (image processing), a matrix used for image convolution * Compute kernel, in GPGPU programming * Kernel method, in machine lea ...

and user modes of the

Win32 The Windows API, informally WinAPI, is Microsoft's core set of application programming interfaces (APIs) available in the Microsoft Windows operating systems. The name Windows API collectively refers to several different platform implementations ...

subsystem. This subsystem includes (kernel-mode), (user-mode), and (user-mode). Any other subsystems listed in the ''Required'' value of the

Registry Registry may refer to: Computing * Container registry, an operating-system-level virtualization registry * Domain name registry, a database of top-level internet domain names * Local Internet registry * Metadata registry, information system for re ...

key are also started. *Creates

DOS DOS is shorthand for the MS-DOS and IBM PC DOS family of operating systems. DOS may also refer to: Computing * Data over signalling (DoS), multiplexing data onto a signalling channel * Denial-of-service attack (DoS), an attack on a communicat ...

device mappings (e.g. CON:, NUL:, AUX:, COM1:, COM2:, COM3:, COM4:, PRN:, LPT1:, LPT2:, LPT3:, and drive letters) listed at the registry key. This can be used to create permanent

subst In computing, SUBST is a command on the DOS, IBM OS/2, Microsoft Windows and ReactOS operating systems used for substituting paths on physical and logical drives as virtual drives. Overview In MS-DOS, the SUBST command was added with the r ...

drives. *Creates

virtual memory In computing, virtual memory, or virtual storage is a memory management technique that provides an "idealized abstraction of the storage resources that are actually available on a given machine" which "creates the illusion to users of a very ...

paging files. *Starts , 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 Task Manager, previously known as Windows Task Manager, is a task manager, system monitor, and startup manager included with Microsoft Windows systems. It provides information about computer performance and running software, including name of ru ...

. It then waits for either or to end, at which point Windows will shut down. If the processes do not end in an expected fashion, may hang the system, or a bugcheck will occur. It also initiates new user sessions when needed. The Local Session Manager Service () sends requests to SMSS through the Asynchronous Local Inter-Process Communication (ALPC) port to start new sessions.

See also

References

Further reading