Feature: Double your graphics power

PC systems with two graphics cards are currently the ultimate for high-tech enthusiasts. Graphics cards from ATI (Crossfire) or Nvidia (Scalable Link Interface or SLI) bring 3D games to your screen with the highest possible graphics quality.

The games run smoothly at the highest quality settings and resolution. Not only does this make 3D shoot-’em-up, driving or flying games look much better, but it also brings a new level of realism to business simulators.

We’ve compared the performance of rival architectures from ATI and Nvidia and outlined the best combination of motherboard and graphics card, as well as explaining what to watch out for during installation of the systems.

We’ll give you the most important results straight away: ATI systems are a bit faster, but those from Nvidia are a little easier to install.

Either a Crossfire or an SLI system will deliver an impressive boost in performance when compared to a single-card solution; according to the application, performance can be up to 90 per cent better.

In the early days of dual-graphics system programming, the developers concentrated exclusively on increasing the frame rate for 3D games.

Today, the focus is also on improvements in overall picture quality. The continuing fascination with 3D is not being ignored, and the range of possible settings for edge smoothing and anisotropic filtering is being expanded by developers.

Very similar 3D performance
When it comes to 3D performance, the ATI and Nvidia graphics platforms in comparable price/performance classes are almost identical.

In the high-end class, however, the ATI Crossfire combination using two Radeon X1900 XTs is just ahead of the Nvidia SLI setup with two Geforce 7800 GTXs.

The fastest ATI combination achieves an impressive 76.4 frames per second (fps) with the resource-hungry 3D game benchmark Far Cry at 1,280 x 1,024 resolution, while the equivalent Nvidia setup rates a ‘mere’ 63fps.

In practice, however, you can’t really tell the difference.

Control four screens
For users who do a lot of multitasking, dual-graphics systems offer a particular advantage.

There are four VGA outputs, so you can attach up to four monitors, and a separate application can run on each monitor.

If you activate the dual-monitor option in the relevant driver, four independent video outputs are available for use, and Windows XP will support up to 10 monitors.

In respect of multitasking, Nvidia has included a special Finance screen profile in its drivers for use in the financial and stock-trading environments.

Another possibility is to display the same application simultaneously on several monitors. Only a few games, such as Microsoft’s Flight Simulator 2004, currently support multi-desktop output.

For example, when running Flight Simulator you can show a different view on each screen. In the case of a photo editor, you can drag the tool palettes onto a separate monitor to keep the image unobstructed.

A word of caution, however: with multi-display applications, you do not get the doubled graphics performance of a Crossfire or SLI system. The only advantage here is in the four monitor connections.

Platforms for SLI and Crossfire
For dual-graphics systems, you need a special motherboard with two PCI Express x16 or x8 interfaces and, unsurprisingly, two suitable graphics cards.

If you are on a limited budget, you could configure a system with, for example, two low-cost Geforce 6600 SLI cards at about £80 each and a motherboard for about £60.

The upper end is currently represented by Crossfire systems, with Radeon X1900XT cards costing about £400 each.

Plenty of manufacturers make motherboards using the Nforce4 SLI chipset needed for Nvidia SLI cards.

For ATI’s Crossfire the choice isn’t so great; you can choose between boards using ATI’s Crossfire Edition of the Radeon Xpress chipset or Intel’s 975X chipset.

A fast CPU is important
Can you increase performance further with a dual-core processor on the motherboard? The answer is no, because the CPU speed is more important than two processor cores with 3D games.

At the moment, the fastest single-core chips available from Intel or AMD run at higher clock speeds than the fastest dual-core processors.

The processor should have a speed of at least 3GHz or the CPU can become a bottleneck for graphics performance.

Whether you are using ATI or Nvidia products, you need a power supply unit (PSU) rated at a minimum of 500w, as a single high-end card can draw well over 100w. Any less and there can be crashes in 3D operation.

In spite of this, dual-graphics systems are not always power wasters, especially the higher-end cards, which incorporate power-saving tricks from notebook technology.

If you’re using only an office suite, for example, the graphics driver switches to 2D mode in which the core speeds are reduced and some processing modules are turned off.

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