Hardware Reference
In-Depth Information
Using multiple monitors requires an independent video signal for each display. Starting
with Windows 2000, this is most commonly done by using Dualview—a single graphics
adapter with two video outputs, also known as a
dual-head graphics adapter
. It is also
possible to use two or more video cards, but this approach is used today only if three or
more displays are used.
Whenmultiplevideoadaptersareinstalled,thesystemidentifiesoneofthevideoadapters
as primary. The primary adapter is sometimes called the
VGA adapter
and is the one that
displays the POST (Power-On Self Test) and BIOS Setup screens. This is a function of
the motherboard and motherboard BIOS. Most modern BIOSs allow you to choose the
primary display adapter via a setting in the BIOS Setup. Normally the options are on-
board (built in), PCI, or PCIe (AGP on older systems with an AGP slot). For the PCI and
PCIe selections, if you have multiple adapters installed, the primary will be the one in the
highest priority slot.
If the BIOS does not let you select which device should be the primary display, it decides
solely based on the priority of the buses or slots in the machine. Depending on the BIOS
used by your system, you might need to check in various places for the option to select
the primary display adapter; however, in most cases it will be in the Video Configuration
menu.
Dualview
Although older video cards often have only a single output, most current video cards
have at least two. With the exception of laptops, the same is true for most motherboard-
basedvideoadapters.Laptopshavealmostalwayshaddualviewgraphicsadapters,where-
as most desktop motherboards have not until recently.
Adualviewcardispreferabletousingtwoseparatecardsbecauseonlyoneslotisused,as
arefewersystemresourcesandevenpower.Thetypesofvideooutputsondual-headcards
can vary, so make sure you choose a card that has the outputs you need or that you can
change the existing outputs via adapters. Digital outputs such as DVI, HDMI, and Dis-
playPortarepreferredbecausethesecannormallybeconvertedtootherswithinexpensive
adapters.
Homogeneous Adapters
The best solution for running multiple graphics adapters in a single system is to ensure
they are homogeneous. This means that they use the same driver, which implies that they
mustalsohavechipsets fromthesamemanufacturer (suchasAMD.ATIorNVIDIA)and
from compatible families within that chipset manufacturer. Using multiple homogeneous
adapters is supported in Windows 98/Me (up to nine total displays) and in Windows 2000
