R520 and CrossFire: So Far Living Only on Paper
ATI Technologies entered the year 2005 with a widest range of products for any user, from the high-performance RADEON X850 XT Platinum Edition to the low-end RADEON X300 and RADEON 9550. Its top-end graphics cards were only inferior in performance to SLI configurations made out of two GeForce 6800 Ultra or GT. The only drawback of ATI solutions was the lack of support of Shader Model 3.0, but that was hardly a serious problem as few available games required it.
At the beginning of May, the Canadians launched another new product, RADEON X800 XL 512MB, but it was hardly a significant event. As our tests proved, 512 megabytes of memory this graphics card is equipped with do not improve its performance much. It is only in Half-Life 2 and in F.E.A.R. Demo that we can see some performance gains, and only in highest resolutions. So much memory might be of some help in resolutions above 1600x1200, but the performance of the RADEON X800 XL GPU would become a bottleneck then. Moreover, a majority of CRT monitors do not support resolutions above 1600x1200, while mass-produced TFT panels are limited to 1280x1024 resolution. So, the RADEON X800 XL 512MB turned to be a niche product targeted only at enthusiasts who just wanted to have a graphics card with 512MB of memory and were ready to pay $449 for it.
On the last day of May ATI also announced its own vision of a multi-GPU technology. Long known under the codenames of AMR and MVP, the new technology was called CrossFire in the end. Two new chipsets, RD400 and RD480, were introduced alongside for building CrossFire-compatible mainboards for Intel and AMD processors, respectively.
Regrettably, the flexibility of the Crossfire technology fell short of what had been rumored and expected. ATI graphics processors don’t have any built-in logic that would allow them to join in pairs, so Crossfire is implemented by means of an external chipset called Compositing Engine. This engine is responsible for sewing together the image fragments rendered by the different cards. RADEON X800 and X850 graphics cards that have that chip on board acquired the words “CrossFire Edition” in their names. In fact, graphics cards were divided into “masters” and “slaves”. The Master was equipped with a special DMS connector the slave graphics card was connected to via an external cable.
So, CrossFire proved to be even less configuration-flexible than NVIDIA SLI. With SLI, you only needed a couple of identical cards, while ATI’s technology required a special CrossFire Edition card to be installed in the system. NVIDIA SLI was implemented not only in high-end GeForce 6800/7800 cards but also in cheaper GeForce 6600 GT (and currently in GeForce 6600). CrossFire, on the contrary, was only limited to RADEON X850 and X800 families. In other words, the following graphics card models were announced:
- RADEON X850 CrossFire Edition 256MB (16 pixel pipelines, 6 vertex processors, 520/1080MHz, $549)
- RADEON X800 CrossFire Edition 256MB (16 pixel pipelines, 6 vertex processors, 400/1000MHz, $299)
- RADEON X800 CrossFire Edition 128MB (16 pixel pipelines, 6 vertex processors, 400/1000MHz, $249)
It was not a drawback as two mainstream graphics cards could always be replaced with a single high-performance one, but this approach left no trace of the alleged flexibility of ATI CrossFire. By the way, a 12-pipelined RADEON X850 or X800 can also be used as a “slave” device, but the “master” card will then disable its four “surplus” pipelines, giving you a total of 24 pixel pipelines.
ATI did implement a few exciting things in CrossFire like the SuperTiling rendering mode in which the frame is divided into squares of a 32x32 pixels size and each card renders half of these squares. Another innovation is the Super AA mode that improves the antialiasing quality using the combined power of two graphics cards. Well, we already dedicated a separate review to the CrossFire technology, so you can refer to it for details, if you wish.
One unpleasant thing about CrossFire is that since the announcement it has remained largely on paper. It seems that ATI’s multi-GPU technology will only come to market for real with the R520 chip. Until that moment there is just no sense in promoting CrossFire because a system with two RADEON X850 cards will hardly be faster than a single GeForce 7800 GTX, but will cost much more money.