Introduction

The limitations of CrossFire

Up to this point, one of the chief criticisms most users have had with ATI’s CrossFire technology has been ATI’s requirement of CrossFire master cards. Unlike regular Radeon graphics cards, the CrossFire master cards contain several extra chips which are used to handle the compositing and communication between GPUs. This makes the CrossFire cards slightly more expensive for ATI to produce, and thus with the exception of the Radeon X1950 XTX CrossFire, ATI charged slightly more for them. The CrossFire master cards also tend to be in shorter supply than regular Radeon cards and therefore when you can find them, they tend to be more expensive. This further complicates matters for ATI.

Another drawback of ATI’s CrossFire technology is also its requirement of the use of thick dongles. The CrossFire dongle is responsible for passing the DVI output from the slave graphics card to the master CrossFire card, where it’s then processed by the compositing engine before ultimately being output to your display. This is a lot less elegant than NVIDIA’s SLI technology, where a single SLI cable is used for communication between the two GPUs.

2nd-gen CrossFire on the X1950 XTX

NVIDIA GeForce 7900 cards in SLI

As an alternative to this, ATI has developed a CrossFire solution for cheaper, lower performance GPUs that doesn’t require the use of a CrossFire master card and CrossFire dongle. Instead data is sent over the PCI Express interface. This solution is far from ideal however, as performance is greatly compromised.

Radeon X1950 Pro CrossFire

ATI’s Radeon X1950 Pro: 3rd-gen CrossFire

Fortunately the Radeon X1950 Pro is ATI’s first GPU with built-in support for CrossFire. No special CrossFire master card is necessary, as the technology is integrated into the GPU itself, so every Radeon X1950 Pro card supports the technology out-of-the-box.

Externally ATI’s new CrossFire solution looks similar to NVIDIA SLI. Like SLI, ribbon cables are used for added flexibility, although ATI’s CrossFire cable is a little wider than NVIDIA’s.

CrossFire connectors on the top of the card

The CrossFire cables are connected to the top of the X1950 Pro cards

At the top left corner of every Radeon X1950 Pro lies two 12-bit CrossFire connectors. This is one more connector than NVIDIA requires for SLI. In ATI’s case, the second connection technically isn’t required for today’s X1950 Pro CrossFire implementation (unless you plan on running CrossFire at 2560x2048 at some point in the future), instead ATI has added the second CrossFire connector for future applications where more than two graphics cards may be connected together. Say for instance if ATI were to launch a competitor to NVIDIA’s Quad SLI.

Rather than bundle the CrossFire cable with the motherboard, as NVIDIA and their board partners do with SLI, ATI will instead be including the CrossFire cable with the graphics card. Inside the packaging of each Radeon X1950 Pro card will be one CrossFire cable. When two cards are then purchased together, the end user then merely connects these cables together for CrossFire.

In terms of compatibility, ATI’s Radeon X1950 Pro CrossFire implementation is 100% compatible with all CrossFire-ready motherboards, including Intel’s 975X and P965 chipsets. All you have to do is install both X1950 Pro cards like you would normally, connect the CrossFire cables, and you’re good to go. ATI’s driver handles everything from there, including assigning one board as the master, and the second card as the slave. All the CrossFire rendering modes (scissor mode, alternate frame rendering, etc) carry over unchanged, as well as ATI’s Super AA feature, which brings 8x, 10x, 12x, and 14x AA settings to CrossFire users.


What we wanted to do with today’s article is examine the performance of ATI’s X1950 Pro CrossFire solution, and see how it compares with its intended competition, GeForce 7900 GS SLI. We’ve known for quite awhile that CrossFire’s Super AA modes give ATI’s CrossFire a decisive performance advantage in higher AA modes, but SLI beats CrossFire pretty much everywhere else. With the debut of the X1950 Pro’s internal CrossFire technology though, is CrossFire finally ready to take down SLI? Let’s find out!