As far as I know, each session of AutoCAD only allows one "tab" to be opened, be it the "model tab" or a "layout tab"
A viewport is simply a window into Modelspace, so you can certainly extend AutoCAD across both monitors and create another viewport to display the model exactly as you'd see if from the "Model" tab.
What I mean gents is: with one screen, you can view model space ( single or multiple viewports). Or you can view paperspace, multiple viewports.
In Microstation for example, you can open up to 8 windows of your model, and arrange them over both screens, giving you better visual use of multiple screens.
Perhaps not as natively as you can in MS or in the same way.
Model space and PaperSpace viewports cannot be viewed at the same time strictly speaking as it is either one or the other but then again you can do it as a PS viewport is simply looking back into model space anyway. If you set up your template with paperspace tab with the varying views you need you could get there. You can stretch Acad across 2 monitors. In modelspace you can have tiled viewports looking at different views but all VP's will have the same layer settings. In Paperspace they can have very independant settings to each viewport.
Yes, I know you can stretch the screen over two. That's what I've been doing. Just thought that maybe there was a setting that would allow it with separate windows, that were kinda independent of each other. By the way is there a command that will stretch the one window over the full two screens?
And thanks for the input as usual.
I think it really relies on Windows mechanisms for that functionality. My monitors are different sizes (heights) so it doesn't work very well. Like when I split model space up, the vertical divide is not between the monitors!
In paperspace however you could adjust as you need.