TTWin 3 has two distinct run modes, SDI (Single Document Interface) and MDI (Multiple Document Interface). The default run mode of TTWin 3 is SDI, this means each session has its own instance of the TTWin3 desktop.

MDI uses a common desktop and as sessions are opened they appear within the common desktop as child windows.

The run mode TTWin3 uses is found on the Configure > Preferences > General tile.

If MDI is selected as the current run mode then another option becomes available. This extra option is Save MDI desktop. If this option is enabled, TTWin 3 will remember the child window positions and configuration files that were in use when TTWin 3 was last closed.