Desktop appears either on external monitor or on laptop both never on both?

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http://askubuntu.com – I am having an issue with trying to connect an external monitor to my Dell XPS laptop with Ubuntu 12. Playing with the BusID does not seem to make much difference. My default device, which I thought would be pointing to my laptop screen, is apparantly influecing where my desktop is displayed. If I tell it to load the nvidia driver, my desktop is shown on my external monitor (via HDMI which is the BudID on my second device ??). If i omit the driver, or tell it to load the one for the integrated intel graphics chip, the desktop is displayed on my laptop screen, and this without any other changes (HowTos)