Some time last year nVidia re-introduced a multi-GPU solution for the home environment with the release of SLi. However, being the “first” to the market does have its dis-advantages with unexpected issues popping up. This is exactly what ATI is trying to capitalize at- carefully observing what was right about SLi and what could be improved upon. Lets find out how well ATI utilized their time working on their multi-GPU solution- Crossfire

Now something that might be unknown to many is that ATI had produced their first dual-GPU card in the form of Rage Fury MAXX back in 1999. In fact, ATI is no stranger to having their multiple GPUs work together. They’ve been producing solutions that work with as many as 16 GPUs in OpenGL for Evans & Sutherland which are used for training pilots in flight simulations. So the introduction of CrossFire isn’t exactly a venture into uncharted waters for them.

Lets start with how Crossfire works externally. With SLi, you basically have to configure two things- first an SLI card between the two video cards needs to be setup in SLI mode and secondly, a bridge between the two cards needs to be connected. Once this is done, you boot into Windows, enable SLI and then reboot to put changes into effect. ATI wanted to make things less complicated with Crossfire. They somewhat adopted the old 3DFX Voodoo way of doing things and basically all that needs to be done is a cable connected from one card to the other externally and voila. There’s no need to reboot Windows either as Crossfire can be enabled or disabled on the fly.

One more problem with SLi is that you need to have two identical cards produced by the same manufacturer. For example, you cant mix 6800GT cards by MSI and Gigabyte and expect them to work. At least not without modifying the BIOS of these cards and that too doesn’t guarantee anything- believe us, we’ve tried. With CrossFire, ATI makes things a little better. You will have to purchase a “Crossfire” enabled card as your primary card and the following table shows what works with what.

Card	Price	Works With
Radeon X850 Crossfire Edition/256MB	$549	Radeon X850XT Platinum Edition Radeon X850XT Radeon X850 PRO
Radeon X800 CrossFire Edition/128MB Radeon X800 CrossFire Edition/256MB	$249 $299	Radeon X800XT Platinum Edition Radeon X800XT Radeon X800XL Radeon X800 PRO Radeon X800

As you can see, you need an X850 CrossFire edition card to work with any model of the X850 series by any manufacturer and an X800 CrossFire edition card to work with any X800 model by any manufacturer. So, for example, you can buy an HIS X800 Crossfire edition card and make it work with a standard Gigabyte X800XT or X800XL card. You might be wondering how a CrossFire edition card is different from a standard one. Lets talk about that next.

A CrossFire edition card will feature a compositing engine that, more or less, calculates the load balancing between the two video cards and determines the optimal configuration. Instead of two DVI connectors found in high-end cards today, the CrossFire edition will have one DVI and one DMS connector. A DVI to DMS cable will allow you to connect your non CrossFire edition card into the CrossFire Edition card and then to your display.

One thing that we’re not too fond of on either CrossFire or SLi is that they will only work with their respective chipset manufacturers at the moment. So you cant expect CrossFire to work in an nForce4-SLI motherboard or an Intel chipset board with dual PCI-E x16 slots and similarly, SLi wont work on anything other than an nForce4 setup. While we’re not sure what nVidia’s stance is, as per our understanding, ATI is very much interested in an open platform setup and wouldn’t mind working with “other” chipset manufacturers to allow the CrossFire technology to work on their platform.