Using two monitors can increase considerably their productivity, since it allows you to keep the application window that is maximized working on the primary monitor and open windows with secondary functions (browser, IM, etc..) In the second monitor. The fact that more need not be alternating between the windows just making a big difference, allowing you to concentrate better in doing that.

For those working with graphics, the second monitor offers another interesting possibility which is maintain the image which is working on the primary monitor and move all the toolbars to the side. By using a VM, or access another machine using VNC / desktop / NX, you can use the second monitor to the window on the second machine and so on.

Although little used (the effect is very odd) you can also maximize the window so that they occupy the area of the two monitors as if they were a single screen.

You can even combine the use of two monitors with the use of Synergy (which touched onearlier material), combining the two monitors with the laptop or netbook:

Traditionally, to use two monitors was necessary to use two video cards, which made the configuration problem, since you almost always need to find some old PCI video card for use with the card AGP. However, with the advent of PCI Express cards and dual-head (with native support for two monitors), the configuration has become much simpler.

Today, virtually all of the nVidia cards offboard support the use of two monitors, thanks to TwinView:

In Windows, the setup is basic, since simply activate the second monitor on the properties of the video. On Linux, configuration is simple but has some peculiarities.

As the current boards use a VGA and a DVI connector, or two DVI connectors and most monitors still use low-cost analog VGA connectors, the first step is to get the adapter to the second monitor. Today, they are quite cheap (the generic adapters cost in the range of 25 dollars and you can find for less than $ 5 in dealextreme or on ebay) but can be somewhat difficult to find.

When buying, make sure that the adapter has the pins 8, C1, C2, C3, C4 and C5, which is precisely the pins that transmit the analog signal:

There are some market adapters DVI-D, which have the same format, but do not use the 4 pin.Naturally, they do not serve in Cosso case.

For best results, the ideal is always use two monitors equal, since it is almost impossible to get just the exact same color on two monitors of different brands. However, if you do not mind the image on the second monitor is a little more blue, or a little less clear than in the first, is perfectly possible to use two different monitors, including monitors, combining different resolutions.

After connecting the second monitor, make sure you are using a recent version of the nVidia driver. If by chance you're using driver "nv", install the nVidia driver (available inhttp://www.nvidia.com/object/unix.html) before proceeding, since the nv driver does not support TwinView.

To enable the configuration, you have two options. For those who like configuration files, the simplest option is to open the file "/ etc/X11/xorg.conf" and change the "device", leaving it as in this example:

Section "Device" 
Identifier "NVIDIA" 
Driver "nvidia" 
Option "TwinView" "true" 
Option "MetaModes" "1024 × 1280 × 1024.1280" 
Option "SecondMonitorHorizSync" "30-81" 
Option "SecondMonitorVertRefresh" "56-75" 
Option "TwinViewOrientation" RightOf " 
EndSection

The options are the most important Driver "nvidia" (which enables the use of 3D driver) and Option "TwinView" "true" (which enables the use of TwinView).

Line Option "MetaModes" 1024.1280 × 1280 × 1024 "indicates the resolutions that will be used in both monitors. By using monitors of different resolutions, this is where you specify the resolution of the second monitor, as in: Option "MetaModes" "1280 × 800.1024 × 768.

Line Option "TwinViewOrientation" RightOf "indicates the position of the second monitor in the first, guiding the mouse cursor. The RightOf "indicates that the second monitor is to the right of the first, but the options are also supported:

"LeftOf": The second monitor is on the left. 
"Above" is above 
"Below" Below 
"Clone": The second monitor displays only one copy of the image of the first. This option is useful for displaying the image on a TV or a projector.

The options "SecondMonitorHorizSync" and "SecondMonitorVertRefresh" "56-75" indicate the rate of update supported by the second monitor (example of this configuration is appropriate for most monitors, 17 "). It is actually optional, since the versions of X are able to detect the rates supported by the second monitor automatically. If you do not know the rates used, comment the two lines for the X alone detects the second monitor.

For those who do not like manual configuration, the second option is to use the command "nvidia-xconfig - twinview" as root, letting you configure the nVidia manages the configuration automatically:

# Nvidia-xconfig - twinview

The configuration can also be edited later using the "nvidia-settings" which is installed along with driver 3D:

It is interesting also mark the "Desktop> Window Behavior> Moving> Let the windows are maximized moved / resized, allowing you to move maximized windows between two monitors.Without it, you need desmaximizar the windows, move and then maximize again, what is really impracticable.

If you are using KDE 4, the configuration is within the "canvas" of Systemsettings and, to use Gnome in "System> Preferences> Video."

Two desktops: In conclusion, it is also possible to have two monitors displaying two separate desktops, each with its own bar of tasks and their own set of open applications. This mode is more complicated to configure the TwinView and offers the disadvantage of not allowing the move windows between monitors.

However, some prefer this method precisely because of the separation. If you want to test, make a backup of the file "/ etc/X11/xorg.conf" to setup TwinView and manages another from the original setting. 
To begin, we must double the "Device" file, like this example:

Section "Device" 
Identifier "Card0" 
BusID "PCI: 1:0:0" 
Driver "nvidia" 
Screen 0 
EndSection

Section "Device" 
Identifier "Card1" 
BusID "PCI: 1:0:0" 
Driver "nvidia" 
Screen 1 
EndSection

See the second section USA a different identifier (Card1) and specifies the second monitor (Screen 1) instead of first.

Option BusID "PCI: 1:0:0" is necessary and indicates the hardware address used by the card (you can check it through the output of command "lspci"). If you are using a PCI Express card slot in the first espetada the x16 motherboard, the address will always be "PCI: 1:0:0", as in the example. Note that the two sections specify the same address, since the two monitors are stuck in the same plate.

Then, we must also duplicate the configuration of the monitor. If the two displays are equal (or pay the same rates of update), you can simply double the section, changing only the identifier, as in:

Section "Monitor" 
Identifier "Monitor0" 
VendorName "SAM" 
ModelName "SAM011e" 
HorizSync 30.0 - 81.0 
VertRefresh 56.0 - 75.0 Option "DPMS" "true" 
EndSection

Section "Monitor" 
Identifier "Monitor1" 
VendorName "SAM" 
ModelName "SAM011e" 
HorizSync 30.0 - 81.0 
VertRefresh 56.0 - 75.0 Option "DPMS" "true" 
EndSection

We must also create a second section "Screen" and set it to use the second configuration of the plate and the second monitor, as in:

Section "Screen" 
Identifier "Screen0" 
Device "Card0" 
Monitor "Monitor0" 
DefaultDepth 24 
Option "hw_cursor" 
Subsection "Display" 
Depth 24 
Modes "1280 × 1024" 
EndSubsection 
EndSection

Section "Screen" 
Identifier "Screen1" 
Device "Card1" 
Monitor "Monitor1" 
DefaultDepth 24 
Option "hw_cursor" 
Subsection "Display" 
Depth 24 
Modes "1280 × 1024" 
EndSubsection 
EndSection

In conclusion, it is missing only edit the section "ServerLayout" at the beginning of the file, specifying the two screens and the position of each relative to one another:

Section "ServerLayout" 
Identifier "Xorg" 
Screen 0 "Screen0" leftOf "Screen1" 
Screen 1 "Screen1" rightOf "Screen0" 
InputDevice "Keyboard0" "CoreKeyboard" 
InputDevice "Mouse0" "CorePointer" 
EndSection

As you can see, the setup is more complicated than the TwinView and the result is not as interesting. If you like the TwinView, better just keep it. :)