Are you having a strange problem with AutoCAD – it opens every drawing in new window creating a new program session? This is really annoying not only because it becomes hard to work with all those drawings, but all those AutoCAD sessions can slow down your Computer. Another problem that you might have is being unable to open multiple drawings in one already started AutoCAD session.
To start using your AutoCAD normally and have multiple files opened in one session you can try changing two system variables – TASKBAR and SDI
TASKBAR command controls whether multiple open drawings are displayed separately or grouped on the Windows taskbar.
If when you type in the command the default value is set to 0 this will mean that it will display only the name of the current drawing in the windows taskbar. Just change the value of 1 and your AutoCAD will work as previous.
SDI or Single Document Interface
If the SDI system variable is not set to its default value 0, but to value 1, 2 or 3 it enables single-document mode, in which only one drawing is allowed to be open at a time.
To bring back old behavior just type in the command line SDI and then enter 0.
Some applications designed for older versions of AutoCAD may set the SDI system variable to a different value for compatibility reasons.
Different values of SDI system variable trigger different type of behavior.
0 – Multiple drawing interface enabled
1 – Multiple drawing interface disabled
2 – Multiple drawing interface disabled by an application that does not support multiple drawings
3 – Multiple drawing interface disabled by user and by an application that does not support multiple drawings