This is what I was looking for. A bit complicated, but finaly it works. Thanks a lot

Got the issue. Both instances starts the C:\Users\USERNAME\AppData\Local\DOSBox\dosbox-0.74.conf But how to get rid of it?

I did. But it is not what I need. I would start two diffrent Instances with diffrent settings. Instance 1 should listen to COM1 and Instance 2 to COM2. If I start these 2 instances (2 Copys of DosBox with diffrent setting in the "DOSBox 0.74 Options") only one of them starts... but this starts twice …

Is it possible to run DosBox twice at same time? I need two instances of it.