OS/2 uses sessions to help the user move from one application to the next without disrupting the screen display of an application.
A session consists of at least one process and a virtual console-buffers for keyboard and mouse input and either a character-based, full screen or a Presentation Manager window. When the system creates a session, the process in the session displays output in the screen or window. The user can view the output and supply input by moving to the session. The user moves to a session by pressing the Alt+Esc key combination, by selecting the title of the session from the Window List, or, for windowed sessions, by clicking the mouse in the session window.
A child session is under the control of the session that creates it. The session that starts the child session is called the parent session. Any process in the parent session can exercise control over a child session.
An unrelated session is not under the control of the session that started it. The process that creates the unrelated session cannot select it, make it nonselectable, bind it, or end it, nor can any other session. DosStartSession does not even return a session identifier when an unrelated session is started. Unrelated sessions are controlled entirely by the user. When OS/2 starts new sessions, it starts them as unrelated sessions.