Peut être HS, mais voilà ce qu'on peut lire dans le manuel de sa CM(pas très complet d'ailleurs,surtout à propos des "Jumper" ):
This motherboard supports Multi Monitor upgrade. With the internal onboard VGA
and the external add-on PCI Express VGA card, you can easily enjoy the benefits
of Multi Monitor feature. If you plan to enable the function of onboard VGA, please
enter the option “Share Memory” of BIOS to adjust the memory capability to
[16MB], [32MB], [64MB], or [128MB]. Please note that the value you select should
be less than the total capability of the system memory. The default value of “Share
Memory” is [Auto], which will disable onboard VGA function when installing VGA
card. After setting up BIOS, you can install VGA cards and VGA card drivers to
enjoy multi-monitors.
Le manuel:-->http://www.asrock.com.tw/Drivers/Manual/K8NF4G-SATA2.pdf<--