Multiple Monitor Support has two components: The hardware component and the software one. The following paragraphs take a look at these components in detail.

The Hardware Component

The hardware component in Multiple Monitor configurations refers to the ability of the display card to support more than one display outputs that can be configured independent of one another. The display card should be able to support and allow resolutions and color depths for each monitor separately.

In addition to being able to use the display outputs independently, one should also consider the use of display processor (known as Graphics Processing Units - GPUs) to drive the outputs. The GPUs reside on the display card and the cards can "time-share" the GPUs to the display outputs or can have dedicated GPUs per display output. For display intensive applications, dedicated GPUs per display output gives a better performance than the time-shared one. The other factor to consider is the amount of memory available to each of the GPU. The amount of memory directly affects the display resolution and color depth. As a side note, a true color (32-bit color) 1024 x 768 display resolution requires 3MB of display memory per monitor.

Most of the new laptops have dual-monitor support built-in. The laptop display forms one monitor and the additional display output forms the second monitor output that can be connected to the projector.

The Software Components

Once you have the necessary hardware in your machine, its the turn of the software to recognize the hardware's capabilities and utilize them.

The Operating System

The operating system (like Microsoft Windows) needs to recognize multi-monitor configurations and provide a vendor-neutral way of accessing the features of such configurations. The applications (such as PowerPoint) use this vendor-neutral way to provide better features. Microsoft Windows 98, Me, Windows 2000, XP, 2003 all have built-in support to recognize multi-monitor configurations.

The Display Driver

The display driver software component recognizes the multi-monitor hardware (the display card) and tells the operating system about it. Normally, the display driver tells the truth! It tells the operating system the actual number of monitors connected to the system. There are configurations where there is a mismatch between the actual number of monitors attached to the machine and the number of them seen by the operating system. The display cards or the display drivers can support multiple modes of operation. The following are some of the popular modes:

Multi-monitor Clone

Most of the multi-monitor display cards and their drivers have the ability to "clone" the content of one monitor to the other monitors. In the Multi-monitor Clone mode, the operating system is informed that the machine has only one monitor when it actually has multiple of them. Behind the scenes, the display card or the display driver replicates the content of one monitor to the other monitors. In the clone mode, the applications (including PowerPoint) as well as the operating system sees only one monitor. They are not even aware that the output that they produce gets copied over multiple monitors.

In the clone mode, one of the monitor is selected as the primary one. It is this monitor that the operating system sees. All other monitors usually have the same display resolution and color depth as the primary monitor.

The Clone mode doesn't require the operating system to have multi-monitor support. This mode can be made available on Windows 95 and Windows NT too.

This mode is supported by all laptops and becomes active when you toggle between internal and external displays on the laptop.

Multi-monitor Span

Normal monitors have a 4/3 width to height display ratio. The 640x480, 600x800, 768x1024, 1280x1024, etc all fall under that ratio. Plasma displays may have 16/9 width to height ratios. The Multi-monitor Span mode makes the display span the entire desktop (usable area) across multiple monitors. Like in the Multi-monitor Clone mode, the operating system is shown only one monitor and is told an abnormal display resolution. For instance, if there are two monitors configured as sitting side-by-side, then the operating system would be told that the display resolution has 8/3 ratio - twice the normal width, that is.

Like the Clone mode, the Span mode too doesn't require the operating system to recognize and support multi-monitor configurations. The Span mode can be made available on Windows 95 and Windows NT.

True Multi-monitor

The Clone and Span modes tell the operating system that only one monitor is present on the machine. It doesn't give control over individual monitors to the operating system but it doesn't require the operating systems to have support for multiple monitors. In the True Multi-monitor mode, the display driver informs the operating system about the actual number of monitors attached to the machine. It allows each monitor to have its own display and allows each monitor to have its own display resolution and color depth.

The applications such as PowerPoint recognize this mode and enable features like the Presenter View in the presence of this mode.

PowerShow (http://officeone.mvps.org/powershow/powershow.html) add-in utilizes True Multi-monitor mode to

• Show different slide shows on different monitors simultaneously.
• Provide the span support for individual slide shows. Using PowerShow, you can control what slide show would span how many monitors.
• Provide you with the option to let you view the speaker notes on the laptop while beaming the slide show through the projector.

Who manufactures multi-monitor display cards?

Click here to find out how to configure your display card for True Multi-monitor mode.