TTWin3 has two distinct run modes, SDI (Single Document Interface) and MDI (Multiple Document Interface). The default run mode of TTWin3 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, TTWin3 will remember the child window positions and configuration files that were in use when TTWin3 was last closed.