Hardware Reference
In-Depth Information
portions of the virtual desktop, enabling you to place the open windows for different applications on
separate monitors and move them around at will.
Although having three or more displays is entirely possible, just adding a second monitor can be a
boon to computing productivity. For example, you can leave an email client or word processor
maximized on one monitor and use the other monitor for web browsing, research documents, and
more.
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.
When multiple video adapters are installed, the system identifies one of the video adapters 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 onboard (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-based video adapters.
Laptops have almost always had dualview graphics adapters, whereas most desktop motherboards
have not until recently.
A dualview card is preferable to using two separate cards because only one slot is used, as are fewer
system resources and even power. The types of video outputs on dual-head cards 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 DisplayPort are preferred because these can
normally be converted to others with inexpensive 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 must also have
chipsets from the same manufacturer (such as AMD or NVIDIA) 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 and later (up to 10 displays) using any combination of
single- or dualview adapters. The installation is simple because only a single driver is required for
all the adapters and displays.
Because AMD and NVIDIA use a unified driver architecture to support their current product lines,
you can use two (or more) AAMD-based or NVIDIA-based cards to create the desired homogeneous
multiple-monitor configuration. The specific cards and even chipsets can be different, as long as they
