I suppose it's only natural that, with PCs growing ever more powerful and capable of performing multiple tasks at once, we'd put them to use doing just that. And the more tasks you have going on at once, the more constrained you'll be by the limited desktop area provided by even a screen capable of resolutions as high as 1600x1200. The next logical step is adding a second monitor, or perhaps a third, but what's going to drive those extra monitors? You could go with an AGP card plus an additional PCI card to drive that auxiliary display, but PCI graphics cards aren't easy to find, especially if you want something with good video signal quality. Why not just run two or more displays with a single graphics card?

If you're ready to take the multimonitor plunge, you have a few choices. There's ATI's HydraVision, Matrox's Dual and TripleHead, and NVIDIA's nView. Each multimonitor system juggles hardware compatibility with software features in an attempt to make the most of an multimonitor desktop. Which one is right for you? Let's find out.

Multimonitor setups explored
For some time, Windows has been able to recognize multiple graphics cards in a single system. Years ago, it was quite convenient simply to add a PCI video card in addition to a primary AGP card to support a secondary display. In time, graphics companies caught on to the multimonitor idea and started supporting multiple monitors on a single graphics card. It's a good thing they did, since good PCI graphics cards are so hard to find these days—just ask anyone with one of Shuttle's non-AGP-equipped cubes.

Windows XP allows multiple-output graphics cards to drive multiple displays to create a single, unified Windows desktop in an expanded workspace. WinXP will also allow a secondary display to mirror the contents of a primary screen. Really, it's up to you how you make the most of a couple of monitors.

That's all there is to multimonitor graphics, at least on the surface. However, there are at least a few compatibility problem areas to keep an eye on, and a lot of feature differentiation between offerings from various companies. I've highlighted some particular areas of concern below.

Some of the above terms and categories may not be clear for those unfamiliar with multimonitor setups, so I'll go over them one by one. Incidentally, I'll try to keep track of functionality in both Win2K and WinXP through the course of this article, but the various multi-display implemantions vary in quirky ways between Win2K and XP. My primary focus will be Windows XP, since it's the newer OS.

• Independent monitor settings - When running an extended desktop on a multimonitor graphics card across multiple displays, Windows XP sees each monitor individually. This means that you can manipulate each display's resolution, refresh rate, and color depth independent of other displays in the multimonitor setup.

  Here, compatibility issues arise with Matrox's TripleHead three-screen configuration, which we'll cover more a little later. Additional incompatibilities also arise with Windows 2000, where only Matrox's DualHead and NVIDIA's nView are capable of adjusting the resolution, refresh rate, and color depth of multiple monitors independently.

• XP desktop support - There are two primary ways to display a Windows XP desktop on multiple monitors, you can stretch it or extend it. A stretched desktop treats a multimonitor configuration as a single, widescreen display and requires that each monitor's settings (refresh rate, screen resolution, and color depth) be the same. Though you are limited to equal monitor settings, a stretched desktop lets the Windows taskbar extend across all the screens in a multimonitor setup.

  If you don't need your taskbar stretching across multiple monitors, or if you want to run independent monitor settings, you'll need to run an extended Windows desktop. Here, only the actual desktop area (not including the taskbar) extends to auxiliary monitors, and Windows sees the configuration as a series of individual displays. With an extended desktop, you can adjust the orientation of auxiliary displays to be above or below your primary display rather than locked down beside it in a widescreen stretched desktop.

• 3D acceleration spanning - Just because you can stretch or extend your desktop area over multiple monitors doesn't mean that a multimonitor graphics card's 3D acceleration will necessarily have the same flexibility. This category is particularly important for 3D professionals looking to extend their effective workspace, but it's also important to gamers looking for a widescreen gaming across multiple monitors.

• Virtual desktop limit - All the multimonitor graphics cards we're looking at today support multiple virtual desktops that further extend Windows' desktop real estate. The implementations are actually quite similar, with the primary difference being exactly how many virtual desktops are supported. Despite theoretical limits, though, the number of virtual desktops that a machine can handle, and that your brain can realistically manage, is likely to be well within the capacity of even HydraVision's nine-desktop limit.

• Intelligent monitor detection - Having a multimonitor setup is great, but what happens when your buddy's over for some LAN gaming action and wants to borrow one of those monitors? If you unplug a monitor and reboot, HydraVision and nView automatically turn off any multimonitor settings and reduce your desktop to a single display. Dual and TripleHead, however, retain an extended desktop even after a reboot with only a single screen. This might not seem like a big deal, but if you have applications set to open on the missing display, you're going to have a hard time getting at them until you plug that auxiliary monitor back in.

• Application position memory and preferences - While all the multimonitor products we're looking at today will remember an application's window size, monitor, and desktop position, Matrox and NVIDIA offer further controls that can be bound to individual applications. Matrox's settings pertain only to 3D applications and their preferences for things like antialiasing, but nView is capable of manipulating various multimonitor window properties on an application-by-application basis.