Using Dual Video Output
The video circuits of most laptops support two video outputs: one to the built-in LCD panel and one for external devices. The external output is not enabled by default, but you can switch between the internal and external displays using a function key.
More advanced configurations of the two outputs are supported by some video cards. For example, you can configure a single large desktop spanning both displays, or set up the external display to show a subset of what is shown on the internal display.
How Do I Do That?
Output from one card to multiple monitors is supported only by some drivers. The most commonly used ones are the NVIDIA and ATI proprietary drivers, and the open source Radeon driver. All of these drivers have some limitations; for example, the NVIDIA driver, when used on a laptop, will always configure an external monitor as primary (screen 0), and the ATI drivers permit only general monitor positioning (you can specify that one monitor is to the right of another, but you can’t indicate a difference in their vertical alignment).
Configuring dual video on an NVIDIA card
Note that for the changes described in this section to take effect, you will need to restart the X server in one of these ways: changing to runlevel 3 and then back to 5, restarting the system, or terminating the running X server with Ctrl-Alt-Backspace (save your work first!).
First, configure and test your system using the NVIDIA proprietary driver (see Lab 5.3, “Using Repositories ...