by Alexey Stepin , Anton Shilov
01/23/2006 | 11:52 AM
Any new technology, especially a promising one, encounters all manner of obstacles as it is finding its way into the market. Although it may have tremendous potential and offer unique opportunities, the new technology often suffers from numerous imperfections and flaws but it sheds them as the developers are polishing it off. So it’s only after the required level of reliability and compatibility is achieved that the user can enjoy the final product as it was conceived by the developer.
<%BANNER[article]%>NVIDIA’s multi-GPU SLI technology was likewise born with huge potential, but didn’t work at all or worked incorrectly with a number of games. Some critics were skeptical about the technology relying heavily on the software, but this eventually turned to be the salvation. In fact, the hardware part of NVIDIA SLI technology was originally designed very cleverly and needed no later improvement that would have been quite costly. At least it would have taken more time and money than the company spent to perfect its ForceWare driver. After a while the incompatibility problems were solved and SLI even acquired some new features like better-quality full-screen antialiasing modes and the option to synchronize the linked graphics cards via a PCI Express bus.
The technology got highly popular among hardcore PC gamers as it long remained the single readily available multi-GPU technology on the consumer 3D graphics market. There was just no other alternative. This monopoly was broken on September 26, 2005, with the actual release of the CrossFire technology by ATI Technologies (for details see our review called Swords Crossed: ATI CrossFire Platform Review). The CrossFire technology had first been announced back on the 30th of May, but had remained on paper due to technical problems (for details you can check out our article called ATI Crosses the Swords: Multi-GPU CrossFire Technology Previewed). Well, we should probably talk only about an attempt to break NVIDIA’s monopoly because it wouldn’t be a big mistake to call that attempt a failure.
The problem with the original CrossFire was that ATI had only out-dated RADEON X850/X800 series processors then which didn’t support modern graphics technologies and were far inferior to the GeForce 7 series in performance. ATI’s approach to creating a multi-GPU technology was not perfect, either. Contrary to NVIDIA, ATI put an emphasis on the hardware part of the technology and tried to make CrossFire as independent from software and drivers as it could possibly be. To implement this concept in silicon, a special mechanism for sewing together the parts of the frame rendered by the different GPUs was necessary. They created it basing on the programmable Xilinx Spartan-3 field programmable gate array (FPGA) that consisted of 400 thousand gates.
Unfortunately, there was a flaw in the Compositing Engine (as the “image-sewing” unit was called) which almost ruined the whole concept. How? A Master card with a Compositing Engine on board was connected to a Slave via an external cable and the data were transferred through a DVI interface, thus requiring a TMDS receiver to be converted into the format the Compositing Engine could understand. The Engine actually included a single-channel 165MHz TMDS receiver, but these characteristics of the receiver limited the maximum display mode to 1600x1200 at 60Hz refresh rate. Moreover, even if CrossFire-compatible Master cards of the first generation had carried a receiver with a higher operating frequency or two ordinary receivers coupled in dual-link mode, the mentioned limitation would have still persisted as ordinary RADEON X850 and X800 graphics cards were equipped with single-channel transmitters that supported single-link mode only.
Thus, the first version of CrossFire was in fact limited to 1280x1024 resolution, but high performance in high resolutions is among the main features of any multi-GPU technology, isn’t it? Large TFT monitors capable of working at 1600x1200 were and are rare and expensive, while using 1600x1200@60Hz mode on a CRT display is prohibited for ergonomic reasons – you’ll strain your eyes in no time at such a low refresh rate.
So the first implementation of the multi-GPU technology from ATI was technically a failure, especially since there were some software-related problems besides the defective design of the Compositing Engine. Despite ATI’s claiming CrossFire’s independence from software, 7 out of 21 games we used in our tests (see this article for details) had a zero or even negative performance gain. With the above-mentioned hardware deficiencies and after the arrival of NVIDIA’s new-generation and faster graphics cards, CrossFire had no real market perspectives in its original implementation. On the other hand, we then said that the next version of ATI’s multi-GPU technology might come out on new-generation graphics processors, free of the original flaws and competitive against NVIDIA’s SLI. So today we are going to see if our expectations have come true because ATI has introduced its RADEON X1800 CrossFire Edition graphics card to the public!
We gave you a detailed insight into ATI CrossFire technology in our earlier reviews (Swords Crossed: ATI CrossFire Platform Review and ATI Crosses the Swords: Multi-GPU CrossFire Technology Previewed), so we are going to sum up just the basics here.
The main point of difference between ATI CrossFire and NVIDIA SLI is that the parts of the image rendered by the different GPUs are combined by the hardware, in a special compositing engine that consists of a TMDS receiver, a programmable Xilinx Spartan matrix, and the chips that send the final image onto the screen (a TMDS transmitter and a RAMDAC). The graphics cards in a CrossFire system are connected via a DVI interface with a special Y-shaped splitter cable.
A CrossFire graphics subsystem has four modes of operation – Scissor, Alternate Frame Rendering (AFR), SuperTiling, and Super AA – that differ in the way the total load is distributed between the Master and Slave graphics cards:
The CrossFire rendering mode is selected automatically if the Catalyst A.I. feature is enabled. In this case the choice depends on the API employed by the particular application: SuperTiling for Direct3D and Scissor for OpenGL. AFR is used only when there’s an appropriate application profile in Catalyst. If Catalyst A.I. is disabled, SuperTiling is used for Direct3D games and Scissor in all other cases. The Super AA mode is automatically activated as soon as 8x/10x/12x/14x FSAA is turned on.
That’s about enough of theory, so we can proceed now to the Master graphics card called ATI RADEON X1800 XT CrossFire Edition. It is the heart of ATI’s multi-GPU technology and we’ll use it to describe the features of the new-generation CrossFire.
The RADEON X1800 XT CrossFire Edition doesn’t seem to differ from the ordinary RADEON X1800 at first:
But you can note some differences if you take a closer look at the card. Particularly, one of the TMDS transmitters is partially visible in the bottom left corner, and on the right, in the power circuit, there is an element we haven’t seen installed before. Then, there is now a new duplex connector that looks like two slim SCSI connectors coupled together, instead of the former DMS-59 plug the CrossFire splitter used to be connected to. The change of the connector must have been due to the use of two DVI channels. In any case the older CrossFire splitter can’t be used with the new version of the technology.
The back sides of the PCBs of the Master and Slave RADEON X1800 XT cards differ quite greatly, but only in the area where the Master carries the Compositing Engine. Of course, we were curious to see the card without its cooler:
ATO RADEON X1800 CrossFire Edition
ATI RADEON X1800 XT
It reveals the most important unit of the card – the new Compositing Engine, free from the deficiencies of the older version. The Slave card can now transfer data in dual-link DVI mode, so two Silicon Image SiI163B receivers are employed to receive and convert data into the format suitable for the programmable array. The total bandwidth of these two devices in dual-link mode is 330MHz (2x165MHz). Using the simple formula R=(1.4*X*Y*V)/1000000 , where 1.4 is a device latency correction coefficient, X and Y are horizontal and vertical resolutions, and V is the vertical sync frequency, you can calculate that the new CrossFire system can maintain a refresh rate of 75Hz at 2048x1536 resolution. Monitors that support such a high display mode are rare and expensive, while the more popular 1600x1200 resolution can be used at 120Hz refresh rate, which is more than enough for a most fastidious user.
The programmable Xilinx XC3S400 array from the Spartan-3 series must have been found sufficient for display modes higher than 1600x1200@60Hz, so ATI did not install a more advanced array on the RADEON X1800 XT CrossFire Edition. The Xilinx chips on the RADEON X850 XT CrossFire Edition and RADEON X1800 XT CrossFire Edition are absolutely identical and differ in the die packaging only. The Xilinx XC3S400 programmable array consists of 400 thousand gates, has 8064 logic cells and 43KB of integrated memory. The small rectangular FBGA-packaged chip next to the Xilinx array is a flash memory chip that stores the Compositing Engine firmware.
The introduction of higher display modes means a higher load on the Compositing Engine and the XC3S400 array may prove a bottleneck in the highest resolutions. We will check if it is really so by performing practical tests in real-life applications.
It is possible that the image-compositing logic will be moved right into the graphics processor in future versions of CrossFire, although it’s not profitable to release two versions of the same GPU for Master and Slave cards, considering that multi-GPU configurations account for but a small share of the desktop 3D graphics market. Integrating the Compositing Engine into every produced chip is hardly justifiable, either: the die will be even more complex and the chip yield will be lower with a negative effect on the cost as well as the market price of graphics cards on such GPUs. A more likely way of further development is creating and using a specialized chip instead of the all-purpose programmable array with its companion chips; this may even make the whole image-compositing system a little bit cheaper.
The final image is sent to the digital input of a TFT panel by a pair of Silicon Image SiI170B transmitters with a combined bandwidth of 330MHz. According to ATI Technologies, the maximum resolution available with the new-generation CrossFire is 2560x1600 at 60Hz refresh rate. It means the new graphics subsystem supports such exotic products as the 30” Apple Cinema HD Display for which 2560x1600 is the native resolution.
A three-channel 330MHz, 10-bit ADV7123 digital-to-analog converter from Analog Devices is still employed for connecting the card to monitors with an analog interface. As we have said above, popular display modes are all available, up to 2048x1536@75Hz. So the main drawback of the previous version of the Compositing Engine – its inability to work in display modes higher than 1600x1200@60Hz – has been successfully resolved in the new version.
Talking about drawbacks, the new graphics card lacks TV outputs. It does not support S-Video or RCA because there would have to be an additional TV encoder on the Master card right after the DAC and this would make the Compositing Engine, quite complex as it is, even more complicated. YPbPr output is probably supported by means of a special DVI-YPbPr converter we described in our All-In-Wonder X1800 XL review . As for HDMI, devices with this interface are fully supported because HDMI is actually a variation of DVI – you’ll just need an appropriate (even though not very cheap) cable.
The RADEON X1800 CrossFire Edition doesn’t otherwise differ from the ordinary RADEON X1800 XT which is used as the Slave card in a CrossFire configuration. It also has 512 megabytes of GDDR3 memory in eight Samsung K4J52324QC-BJ12 chips. The graphics processor is clocked at the standard core frequency of the RADEON X1800 XT, i.e. at 625MHz, so the performance shouldn’t be far lower than that of the ordinary card.
As for using the new graphics card together with a RADEON X1800 XL, this is really possible, despite the serious difference in the clock rates of the cards as well as the twice lower amount of graphics memory installed on the X1800 XL. In this case half the onboard graphics memory of the RADEON 1800 XT CrossFire Edition is going to be turned off by the driver, but its operating frequencies will remain intact and there may be situations when the Master is idle waiting for data from the slower Slave card. The efficiency of this configuration will be far from optimal, yet the owner of a RADEON X1800 XL has no other way to improve the graphical performance of his PC by means of CrossFire technology as yet. As far as we know, ATI Technologies doesn’t have a Master version of RADEON X1800 XL in its plans.
The cooling system of the card hasn’t changed since the announcement of ATI’s new generation of GPUs. It is efficient thanks to the high-quality heat-spreader and remains rather quiet even if you are working long in 3D. As earlier, a very thick dark-gray thermal paste, probably Shin-Etsu, serves as a thermal interface between the GPU die and the heat-spreader’s sole. The memory chips have contact with the heat-spreader through elastic rubber-like thermal pads, traditional for products from ATI Technologies.
The RADEON X1800 XT is known to consume over 110 watts of power under load. This is considerably higher than the power consumption of the GeForce 7800 GTX 512, which is about 95 watts. We didn’t specially measure the consumption of our sample of the RADEON X1800 XT CrossFire Edition since the Master card was technically identical to the ordinary one.
The total power consumption of a graphics subsystem consisting of two RADEON X1800 XT can thus be as high as 220W and more, whereas two GeForce 7800 GTX 512 are going to consume about 190W. Considering that SLI and CrossFire technologies are both targeted at computer enthusiasts with a big enough PC budget, it is very likely that the rest of the system components will require a lot of power, too. Our own testbed was powered by a Cooler Master Real Power-450 and was quite stable, but surely a higher-wattage unit would have been needed if we had used a powerful processor like AMD Athlon FX-60 or Intel Pentium Extreme Edition 955. We suppose that a high-quality 500-550W power supply should be enough for stable operation of an ultra-fast computer with two RADEON X1800 XT cards.
We tested the new version of CrossFire technology on our ATI RADEON Xpress 200 CrossFire Edition platform configured like follows:
NVIDIA’s SLI is as yet officially supported by nForce4 series chipsets only, so we had to use another platform to test this technology:
We set up the drivers from ATI and NVIDIA in the same way as always.
ATI Catalyst:
NVIDIA ForceWare:
We decided not to perform the tests in the “pure speed” mode since the performance of such powerful graphics subsystems as RADEON X1800 XT CrossFire and GeForce 7800 GTX SLI would be limited by the performance of the central processor installed in the testbed. Considering that there are almost no games that support resolutions above 1600x1200, we decided to load the multi-GPU subsystems by means of full-screen antialiasing of levels higher than 4x. We chose 8x and 14x FSAA for CrossFire and 8x and 16x for SLI. Current games don’t even suspect such FSAA modes exist, so we have to turn them on forcibly from the driver.
We do not edit the configuration files of the games and select the highest graphics quality settings in each game, identical for ATI’s and NVIDIA’s solutions, except for the flight sim Pacific Fighters that requires vertex texturing for its Shader Model 3.0 mode. The RADEON X1000 series doesn’t support this feature and we have to launch the game in Shader Model 2.0 mode on such graphics cards.
If possible, we use the game’s integrated benchmarking tools to record and reproduce a demo and measure the reproduction speed in frames-per-second, and if not, we measure the frame rate with the FRAPS utility. We measure minimal as well as average fps rates whenever possible to draw a fuller performance picture. Unfortunately, we didn’t have a second sample of GeForce 7800 GTX 512 and had to use a SLI configuration with two ordinary GeForce 7800 GTX as an opponent to the RADEON X1800 XT CrossFire system. We also tested the following single cards in 4x FSAA + 16x AF mode for the sake of comparison:
These games and applications were used as benchmarks:
First-Person 3D Shooters
Third-Person 3D Shooters
Simulators
Strategies
Semi-synthetic benchmarks
Synthetic benchmarks
We carried out a brief check of the image quality provided by SLI and CrossFire technologies in various full-screen antialiasing modes, including extreme/hybrid ones. We took screenshots in Far Cry , Half-Life 2 , and Half-Life 2: Lost Coast at 1280x1024 resolution with 16x anisotropic filtering turned on. We also analyzed the resulting screenshots with the Compressonator utility that reveals discrepancies that hide from the naked eye.
ATI CrossFire | NVIDIA SLI |
FarCry | |
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Half-Life 2 | |
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Half-Life 2: Lost Coast | |
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We think 4x FSAA gives a somewhat better-looking picture on ATI’s graphics cards. If you examine the Far Cry screenshots closely, you’ll note small jaggies on the bars of the grid as rendered by the NVIDIA GeForce 7800 GTX, while there is no such jaggedness on the screenshots we made on the RADEON X1800 XT. In Half-Life 2 , however, the wire fence looks considerably better on the GeForce 7800 GTX – it disappears partially on the RADEON X1800 XT. The image quality in Half-Life 2: The Lost Coast is the same as in Far Cry , but the difference is so small as to evade the naked eye, especially during actual play.
ATI CrossFire | NVIDIA SLI |
FarCry | |
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Half-Life 2 | |
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Half-Life 2: Lost Coast | |
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8x FSAA and 8x SLI FSAA look almost identically on the RADEON X1800 and GeForce 7800 GTX since they are virtually identical from the technical point of view and are 4x FSAA with two times the number of samples. The antialiasing quality is nearly ideal in all cases, but the ATI RADEON again fails to render the fence wire from Half-Life 2 in full, so we should consider NVIDIA the winner of this test.
ATI CrossFire | NVIDIA SLI |
FarCry | |
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Half-Life 2 | |
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Half-Life 2: Lost Coast | |
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The 16x SLI AA mode available on the SLI platform is a combination of two 8xS FSAA modes which were originally hybrid modes by themselves, combining super-sampling and multi-sampling. This mode ensures the best antialiasing quality on small details and the notorious fence wire from Half-Life 2 – the stumbling block of lower-level FSAA modes – is close to ideal here. ATI’s Super AA 14x mode is a hybrid one, too, and combines 6x multi-sampling with additional 2x rotated-grid antialiasing. It handles micro-geometry very well, ensuring a somewhat better image quality than NVIDIA’s SLI AA 16x, but the above-mentioned fence still doesn’t look quite well in this case.
So it is difficult to say what hardware you get the best image quality with in games. ATI’s CrossFire working in Super AA 14x mode is the best at rendering small details, but if there are such objects in the scene as foliage, a wire fence or something, NVIDIA’s SLI platform with its SLI AA 16x mode is unrivalled. As you understand, all these FSAA modes are only really helpful if you can turn them on in real-life games and have a high enough frame rate at that. We are going to show you in the next section of the review if these extreme antialiasing modes are of any use today.
Unfortunately, we could not turn on Super AA in Battlefield 2 . FSAA can only be enabled in this game if the Catalyst driver’s By App option is on, but the game itself does not support FSAA levels higher than 4x.
It is the CPU processing power that limits the performance of a dual-GPU platform here, so we can’t make any comparisons: the RADEON X1800 XT CrossFire has the same frame rate of over 100fps through all the tested resolutions. Note also that the single RADEON X1800 XT is ahead of the single GeForce 7800 GTX due to higher GPU and memory clock rates.
The GeForce 7800 GTX pair is the fastest in FSAA 4x mode as these graphics cards are more effective in OpenGL applications and feature UltraShadow II technology. The RADEON X1800 XT CrossFire is slower, yet this graphics subsystem yields a comfortable 60fps even in 1600x1200.
NVIDIA’s solution is better at doing the more resource-consuming 8x FSAA, but the gap diminishes in higher resolutions. It is doubtable in this case if you can play with comfort in resolutions over 1024x768 because the average performance of both the platforms may go down to below 60fps in 1280x1024.
The situation changes dramatically as soon as we turn on the maximum possible FSAA modes: SLI AA 16x and Super AA 14x. The latter is less resource-consuming (it doesn’t perform true super-sampling), so the RADEON X1800 XT CrossFire platform goes ahead and provides a comfortable frame rate in 1024x768 even. It means this mode may be of some practical value for gamers who want to have the best-looking picture on the screen.
The GeForce 7800 GTX SLI platform boasts a total of 48 pixel pipelines, but its memory is slower than the graphics memory subsystem of the RADEON X1800 XT CrossFire, which also has efficient memory controllers into the bargain. This is why ATI’s solution takes the lead in 1280x1024 resolution, leaving the others far behind, and then yields over 70fps in 1600x1200. Both the multi-GPU subsystems perform close to their theoretical maximums, NVIDIA’s SLI being as high as 100% efficient in 1600x1200!
When we switch over from 4x FSAA to 8x Super AA the RADEON X1800 XT CrossFire remains on top thanks to its fast memory and high pixel shader performance, and 68fps in 1024x768 should be enough for any demanding player. In Super AA 14x mode the performance results were exactly as in Super AA 8x mode. It can indicate that the 14x mode is more power hungry (the difference between the 4x and 6x modes in really tiny for RADEON X1800), but at the same time that there are, theoretically, some performance issues.
Strengthened with a new driver, the CrossFire platform is no slower than the SLI one, and the multi-GPU technologies both permit to play Doom 3 comfortably in all resolutions with enabled 4x FSAA. But take note that the single GeForce 7800 GTX 512 follows closely behind the leaders and two such cards linked in a SLI configuration would most probably be beyond any competition here.
The GeForce 7800 GTX SLI is only sufficient for 1024x768 while the RADEON X1800 XT CrossFire makes the currently most popular resolution of 1280x1024 playable, too. We could not test a SLI configuration of two GeForce 7800 GTX 512, but we again suspect that it would be even faster here.
It’s hard to imagine an owner of a system with two RADEON X1800 XT to have a monitor that wouldn’t support resolutions over 1024x768, but we should note that 14x Super AA is quite permissible with that resolution and doesn’t entail a catastrophic performance hit. There’s only 15fps difference between 14x Super AA and 8x Super AA, but the antialiasing quality is better, although you can hardly spot it with a naked eye, especially in the gloomy interiors of Doom 3 . The GeForce 7800 GTX SLI offers you its 16x SLI AA mode, but 42fps in 1024x768 looks to be too low a frame rate for a 3D shooter with first-person view.
Even if you turn on 4x full-screen antialiasing, Far Cry is not the monster application anymore that used to get ultra-high-end graphics cards to the knees just a little while ago. Today’s highest-performing solutions don’t even show their full power here, being limited by the performance of the system’s central processor. Even the single GeForce 7800 GTX 512 turns in 77fps and more in 1600x1200 resolution, which is very close to the CPU-imposed speed ceiling.
When we switch from the traditional 4x FSAA to 8x Super AA, the RADEON X1800 XT CrossFire system doesn’t slow down too much. We can’t say the same about the GeForce 7800 GTX SLI – this configuration is limited by its slow memory and cannot ensure a comfortable frame rate in 1600x1200.
It is possible to turn 16x SLI AA on in Far Cry , but you’d better switch to the lowest resolution at that – the two GeForce 7800 GTX cards yield about 60fps then. Meanwhile, the RADEON X1800 XT CrossFire platform doesn’t seem to lose much from its having to perform 14x Super AA. The small performance hit of the CrossFire platform is evident here. Besides, the screenshots taken in this game have revealed some differences in anti-aliasing quality, so we cannot blame CrossFire or FarCry for that. It is most likely to be happening because RADEON X1800 XT doesn’t really slow down when switching from FSAA 4x to FSAA 6x.
The Research level is less CPU-dependent than Pier and complex shaders are employed here for per-pixel lighting, so we can make our comparison in 1280x1024 already. In this resolution the RADEON X1800 XT CrossFire is a little better than the GeForce 7800 GTX SLI platform, but CrossFire seems less efficient if you consider the speeds of the single cards.
The GeForce 7 architecture executes the version 3.0 shader code from Far Cry more efficiently, but the SLI system made of two GeForce 7800 GTX cards is far slower than the CrossFire system with two RADEON X1800 XT when performing full-screen antialiasing of level 8x. You can’t play comfortably in 1600x1200 resolution on the GeForce 7800 GTX SLI, but you can on the RADEON X1800 XT CrossFire.
The RADEON X1800 XT CrossFire system slows down but very little as we switch over to the 14x Super AA mode and all the resolutions remain playable. The GeForce 7800 GTX SLI, on the contrary, yields over 60fps in 1024x768 only. A SLI system with two GeForce 7800 GTX 512 would surely have a higher result, but we don’t think it would outperform the RADEON X1800 XT CrossFire here because NVIDIA’s 16x SLI AA algorithm is more resource-consuming.
The low efficiency of CrossFire is what you can see immediately in this test. As opposed to SLI, the performance gain from ATI’s multi-GPU technology is a mere 10-20%. Although the single RADEON X1800 XT is far ahead of the single GeForce 7800 GTX, two such cards in the CrossFire system are slower than the two SLI-linked GeForce 7800 GTX in all resolutions in the 4x FSAA + 16x AF mode.
And as it has happened in the earlier tests, the RADEON X1800 XT CrossFire takes the lead as soon as we switch to more resource-consuming antialiasing modes, available only on multi-GPU platforms. However, F.E.A.R. is such a heavy application that 8x Super AA only makes sense if turned on at 1024x768 resolution because in higher resolutions the frame rate bottoms out to below 25fps and the game doesn’t run smoothly on the screen anymore.
Although SLI AA 16x and Super AA 16x modes are not practically applicable in F.E.A.R. , we should note that the RADEON X1800 XT CrossFire is much better than the GeForce 7800 GTX SLI in this comparison, too. The gap between the two multi-GPU platforms is as big as 300% in 1600x1200 resolution!
A very heavy and graphically advanced application at the time of its release, Half-Life 2 is nothing extraordinary for today’s high-performance graphics cards and multi-GPU configurations. They all have a frame rate of 80fps and higher in this game, except for the single GeForce 7800 GTX which anyway allows playing comfortably with enabled 4x FSAA.
The GeForce 7800 GTX SLI can’t yield a playable frame rate in 1600x1200 when performing 8x SLI AA, while the RADEON X1800 XT CrossFire doesn’t find it a problem at all.
The CrossFire platform has no difficulties switching from 8x Super AA to 14x Super AA whereas the SLI system is too slow even in 1280x1024. The game is playable in 1024x768 on the SLI platform and the image quality is superb then.
The Lost Coast technical demo is far more difficult for the graphics subsystem than the original Half-Life 2 , so we decided to include it into this review, too. At the maximum graphics quality settings the demo requires Shader Model 3.0 support and displays a number of advanced HDR-using special effects.
The CPU still plays a bottleneck in 1024x768 resolution: the GeForce 7800 GTX SLI, the single GeForce 7800 GTX 512 and the RADEON X1800 XT CrossFire all have almost identical results. In higher resolutions the GeForce 7800 GTX SLI is on top notwithstanding its lower clock rates and two times less memory. Moreover, it boasts a higher efficiency because the single GeForce 7800 GTX and the single RADEON X1800 XT have almost the same speeds. Unlike in Half-Life 2 , not all resolutions are playable in Lost Coast . The speed is sufficiently high only in 1280x1024 and only on the multi-GPU platforms even when you use only 4x FSAA.
There are changes in the rankings at higher antialiasing levels, yet the gap between the RADEON X1800 XT CrossFire and the GeForce 7800 SLI remains small in low resolutions. It’s only in 1600x1200 that the ATI platform is quite far ahead, evidently because it has more and faster graphics memory.
The GeForce 7800 GTX SLI loses its speed suddenly when it begins to perform the resource-consuming 16x SLI AA. Contrary to this, the speed of the RADEON X1800 XT CrossFire remains almost the same as in the previous test. Well anyway you may only want to play the game in 1024x768 with this level of antialiasing enabled.
This game is equally unfriendly towards both SLI and CrossFire: it runs slower when you turn on the multi-GPU rendering mode – almost two times slower on the CrossFire platform.
When you turn on SLI AA or Super AA on a multi-GPU system, you do not take some load off the main graphics card because the second card only performs additional full-screen antialiasing for a higher overall image quality. Neither CrossFire nor SLI has any problems here. As for their speeds, ATI’s solution is faster in the same way as the single RADEON X1800 XT is faster than the single GeForce 7800 GTX.
The gap between the competing multi-GPU platforms gets wider as we approach the most extreme FSAA modes and the RADEON X1800 XT CrossFire provides a comfortable frame rate in all resolutions even though it delivers a somewhat worse image quality – the performance of this platform doesn’t lower as much as that of the GeForce 7800 GTX SLI.
There is a mere 3fps of difference between the RADEON X1800 XT CrossFire and the GeForce 7800 GTX SLI, their absolute speeds being somewhere around 110fps. You can note that the efficiency of SLI technology is somewhat higher in this case.
The RADEON X1800 XT CrossFire and the GeForce 7800 GTX SLI platform both deliver a high enough performance at 8x FSAA, but the ATI platform is much faster, being equipped with more of graphics memory.
And like in the previous case, the RADEON X1800 XT CrossFire makes all the resolutions playable, even 1600x1200, and its performance is never slower than 85fps, while the GeForce 7800 GTX SLI only allows using 16x SLI AA in 1024x768.
The efficiency of CrossFire is only about 40%, but the performance gain from SLI technology isn’t bigger than 40%, either. What’s more, the CrossFire configuration made of two RADEON X1800 XT cards is only ahead of the single GeForce 7800 GTX 512 in 1600x1200 resolution. If we had two such cards in the SLI platform, we’d surely get the highest results and a comfortable game speed in resolutions above 1024x768 which are not available to owners of a RADEON X1800 XT CrossFire subsystem.
These numbers are of purely theoretical interest, yet the twofold lag of the GeForce 7800 GTX SLI is a fact.
The GeForce 7800 GTX SLI can’t give you more than 20fps with turned-on 16x SLI AA, but the minimum speed of the RADEON X1800 XT CrossFire is very low here, too, and it means you won’t be able to play the game comfortably using 14x Super AA. Can the upcoming R580 make it possible?
There is almost no effect from CrossFire in Unreal Tournament 2004 as you can clearly see in 1600x1200 resolution. These are probably some driver issues or a flaw in the Compositing Engine, but the latter is rather unlikely.
The RADEON X1800 XT CrossFire is faster at doing 8x Super AA, but the GeForce 7800 GTX SLI follows it closely – the gap is never bigger than 10%. The RADEON X1000 is in general not very efficient in games that don’t have many complex pixel shaders.
As we increase the Super AA/SLI AA coefficient we noticed a very curious thing: the performance of GeForce 7800 GTX SLI didn’t go down compared with what it demonstrated in the previous mode. At the same time RADEON X1800 CT CrossFire dropped down dramatically, which used to be typical only of the NVIDIA multi-GPU platform that supports SLI AA 16x. We repeated the tests multiple times, but with no success: the results remained the same. The problem is most likely to be with the ATI CATALYST drivers, because we have already experienced the performance issues with them in Unreal Tournament before.
Metallurgy demo is not so CPU dependent as Torlan and you can notice the effects of another problem caused by ATI CATALYST drivers in Unreal Tournament 2004. The problem is the relatively low maximum result for the RADEON compared to what the GeForce can reach. Anyway, even if CrossFire does provide a performance increase compared with a single RADEON X1800 XT, this advantage is not very high and doesn’t exceed 6-8fps.
The situation we observe in Super AA 8x/SLI AA 8x is similar to what we see on Torlan level: in 1024x768 resolution the leadership belongs to GeForce 7800 GTX SLI, but in higher resolutions RADEON X1800 XT CrossFire is the winner, because it boasts ore attractive technical specs. The difference can only be observed in one resolution: for the Torlan level it is the 1600x1200, and for the current level - 1280x1024. The performance of both multi-GPU platforms is high enough, so all resolutions in Unreal Tournament 2004 are playable in FSAA 8x + AF 16x.
The problem we have already described during the discussion of gaming performance in Torlan repeats here. In Metallurgy the performance of GeForce 7800 GTX SLI remained the same, while the performance of RADEON X1800XT CrossFire dropped down quite rapidly.
The multi-GPU platforms both boast a near maximum efficiency in high resolutions. CrossFire is never slower than 90fps, SLI than 70fps. That’s more than enough for you to enjoy this game fully. CrossFire’s win comes as the result of the high efficiency of the RADEON X1800 XT architecture at executing version 3.0 shader code.
The three tested resolutions are all available for an owner of two RADEON X1800 XT cards who wants to use 8x Super AA. The GeForce 7800 GTX SLI loses its ground in 1600x1200, slowing down to 23fps as it is doing 8x SLI AA.
The GeForce 7800 GTX SLI has exactly the same speed here; it probably lacks graphics memory to perform 16x SLI AA. Having two times more memory, the RADEON X1800 XT CrossFire passes the test correctly, yielding a playable frame rate in every resolution. The 16x Super AA mode is less difficult than 16x SLI AA after all.
The multi-GPU platform with two RADEON X1800 XT graphics cards is unrivalled in this racing simulator. Once again, we don’t have a second GeForce 7800 GTX 512 to check the performance of the respective SLI configuration which would probably make a worthy rival to the current winner.
The RADEON X1800 XT wins also when we switch from 4x FSAA to multiple-GPU-oriented antialiasing modes.
The gap gets wider: the magnificent image quality provided by 16x SLI AA comes along with a tremendous performance hit which makes high resolutions unsuitable for normal play.
The game depends just too heavily on the CPU performance. There is no difference between the results of the different graphics cards despite the enabled full-screen antialiasing and the fact that the RADEON X1800 works in Shader Model 2.0 mode.
The GeForce 7800 GTX SLI is slower than the RADEON X1800 XT CrossFire in 1600x1200, yet NVIDIA’s platform is still quite powerful to run the game at an acceptable speed – the minimal frame rate is 39fps and the image quality is a little better than the competitor’s.
14x Super AA and 16x SLI AA are now available for all virtual pilots. The NVIDIA platform is limited to 1280x1024, but we guess the performance of two SLI-linked GeForce 7800 GTX 512 cards would be sufficient for the higher resolution, while keeping the superb image quality.
The GeForce 7800 GTX SLI increases its lead over the RADEON X1800 XT CrossFire as the resolution grows. The gap varies from 18-20% in 1024x768 to 60% in 1600x1200 resolution.
The GeForce 7800 GTX SLI wins this test at 8x FSAA, too, notwithstanding the slower memory. This time only 1024x768 resolution is playable.
Even though the 16x SLI AA algorithm takes up a lot of the graphics subsystem resources, the SLI pair of GeForce 7800 GTX cards holds the first place. The RADEON X1800 XT CrossFire follows the leader closely, though.
The shadows rendering acceleration technology helps the GeForce 7800 GTX SLI outperform the RADEON X1800 XT CrossFire in two resolutions out of three. This time around all the top-end graphics cards and multi-GPU systems deliver a playable frame rate in all the tested resolutions.
The two multi-GPU platforms match one another’s performance when doing 8x Super AA and 8x SLI AA, with minor advantage to either side in a particular resolution. Here, 1600x1200 resolution is hardly available for the gamer. Note also the much higher minimal fps rate of the SLI platform.
You can play this game with comfort in 1024x768 resolution on both RADEON X1800 XT CrossFire and GeForce 7800 GTX SLI platforms, but the speed will bottom out less on the latter platform in the most complex scenes. In higher resolutions the ATI platform breaks away because the competitor uses a more difficult FSAA algorithm, but it hardly matters for a practical gamer: 30-35fps is rather too slow for such a dynamic strategy as Dawn of War .
Aquamark 3 is not as informative as it used to be because it has but very few pixel shaders and also depends heavily on the CPU performance, at least when it comes to top-end graphics solutions. Analyzing the numbers you can note that the RADEON X1800 XT CrossFire is on the winning side, yet this is far from a decisive win.
The CrossFire platform enjoys a bigger advantage in the 8x FSAA mode as it is has more graphics memory.
The RADEON X1800 XT CrossFire enjoys a bigger advantage over its opponent at the highest full-screen antialiasing levels, up to 100% in 1600x1200.
The RADEON X1800 XT CrossFire platform scores 26,650 points in 3DMark03 which is the highest result we’ve ever recorded. The SLI configuration with two GeForce 7800 GTX are not far behind, though, and the single GeForce 7800 GTX 512 nearly hit the 20,000 mark and would certainly have a higher total score than the ATI RADEON X1800 XT CrossFire if combined with another such card. That’s why we can’t claim the RADEON X1800 XT CrossFire is an unrivalled leader in this test.
The RADEON X1800 XT CrossFire is faster than the GeForce 7800 GTX SLI in all the three FSAA modes, the gap being as wider as a more difficult FSAA level is turned on. And we’ve got such results in a test that does not match well the complex-shader-oriented RADEON architecture and never uses rendering techniques other than described by DirectX 7.
The RADEON X1800 XT CrossFire wins the second test (again, we don’t count in the performance of a SLI platform with two GeForce 7800 GTX 512 which is yet to be tested in our labs). Unlike in the first test, there is a much smaller difference between the two multi-GPU platforms.
The third test shows a somewhat different picture: the RADEON X1800 XT CrossFire loses its advantage in the extreme FSAA modes and the GeForce 7800 GTX SLI takes the lead at 4x FSAA. We suspect this to be due to the more efficient vertex processors of the GeForce 7800 GTX since the more complex geometry is the single difference of the third test from the second one.
The GeForce 7800 GTX SLI finds the extreme FSAA modes much more difficult than they are for the RADEON X1800 XT CrossFire. The graphics cards in the latter platform have two times more graphics memory which is also clocked at a considerably higher frequency – a very important factor when there’s a huge load on the graphics memory subsystem. Moreover, it is easier to perform 14x Super AA than 16x SLI AA that uses regular super-sampling. In the relatively easy 4x FSAA mode both these platforms have almost the same speed, with a minor advantage on the part of the ATI RADEON X1800 XT CrossFire.
3DMark05 differs from 3DMark03 by using all the modern 3D graphics technologies, particularly very complex pixel and vertex shaders. That’s why the bigger advantage of the RADEON X1800 XT CrossFire over the GeForce 7800 GTX SLI is not to be wondered at.
The RADEON X1800 XT CrossFire is at first not much faster than the GeForce 7800 GTX SLI, and there is a small difference between these two platforms in the 8x FSAA mode, but then the ATI platform is suddenly far ahead as soon as we turn on the maximum antialiasing level. It is not only because the RADEON X1800 XT CrossFire is equipped with faster memory, but also because 14x Super AA is easier to perform than NVIDIA’s 16x SLI AA.
The advantage of the CrossFire platform over the GeForce 7800 GTX SLI is more conspicuous in the second test, even though the test scene itself is smaller.
The RADEON X1800 XT can execute complex shader code very quickly and it is equipped with a lot of fast memory, so you cannot but guess the winner right: the RADEON X1800 XT CrossFire takes the lead at the very beginning of this pixel-shaders-heavy test and increases it hereafter. The GeForce 7800 GTX SLI is not so very far behind at 8x FSAA, and we are sure a SLI configuration with two GeForce 7800 GTX 512 would have even better results.
Now that we have tested the new incarnation of ATI CrossFire technology we can state that it has matured and has completely got rid of the deficiencies of the original CrossFire.
Most important is that the display mode limitations have been removed. Resolutions over 1600x1200 could not be used previously, but now the ceiling is as high as 2560x1600 at 60Hz. That’s an exotic mode indeed, but as for the popular resolutions like 1600x1200, you can now use them at higher refresh rate frequencies, comfortable and safe for your eyes. ATI’s solution of the problem – they installed two TMDS receivers and two TMDS transmitters – may not seem very elegant and certainly makes the Master card more complex, but it works all the same.
Taking a very critical approach we could still find at one disadvantage in the new CrossFire: using an external RAMDAC and lacking a TV encoder chip, this graphics subsystem cannot output to devices with composite or S-Video input. On the other hand, these video interfaces do not provide the best image quality possible and do not match the high-end product class the RADEON X1800 XT CrossFire platform belongs to, so it can hardly be considered a serious drawback. We guess people who can pay the price of this platform have already got modern TV-sets with DVI or HDMI inputs.
Like the RADEON X850 XT CrossFire Edition, the RADEON X1800 XT CrossFire Edition gives you some flexibility in configuring your multi-GPU system. Particularly, it can make up a pair not only with another RADEON X1800 XT but also with a less powerful RADEON X1800 XL. Of course, half the memory won’t be used then and you need to reboot the system to turn on the CrossFire mode. The efficiency of such a configuration would be low due to the big discrepancy in the clock rates of the two cards, yet you can really unite a RADEON X1800 XT with a RADEON X1800 XL and this will work. This option may be interesting to owners of a RADEON X1800 XL.
The previously reported compatibility problems have vanished, too:
It’s only in one game, in the 3D shooter Project: Snowblind, that the multi-GPU rendering mode brought about a negative performance gain, and not only with CrossFire but also with SLI. It means that the problem must be in the game rather than in these two technologies. In the majority of applications we have observed a performance growth ranging from 10-20% in F.E.A.R. (probably due to some problems with SuperTiling) to 80-90% in other games. In three more games the speed proved to be limited by the CPU performance despite our using full-screen antialiasing.
We were also pleased with excellent stability of the CrossFire platform which never hung up and never produced any image artifacts during our tests. This is another sign of maturity, we guess. ATI CrossFire does work now and it works quite well.
So ATI now offers a working alternative to NVIDIA’s SLI, but how appealing this product is? The recommended price of the RADEON X1800 XT CrossFire Edition being $599, the combined cost of the corresponding CrossFire platform will be $1200 – without the mainboard and power supply. This is not too much in comparison with the cost of two GeForce 7800 GTX, which is about $1000. Multi-GPU systems are assembled to make high resolutions with turned-on full-screen antialiasing and anisotropic filtering playable and the RADEON X1800 XT CrossFire looks preferable to the GeForce 7800 GTX SLI in almost all the games we’ve used in this review. The Super AA 14x mode is available most of the time, while SLI AA 16x, although it does ensure a noticeably higher antialiasing quality, is such a difficult algorithm that the performance of the SLI platform sinks below playable level in nearly every game. Moreover, the RADEON X1800 architecture allows using FSAA and HDR simultaneously, while the GeForce 7 architecture does not.
A SLI configuration with two GeForce 7800 GTX 512 may challenge the RADEON X1800 XT CrossFire. It would be faster, but more expensive (up to $1500) and it still wouldn’t allow using FSAA and HDR at once. Moreover, such graphics cards are scarcely available on the market and some PC manufacturers have been delaying their systems with GeForce 7800 GTX 512 by a month and longer at the time of our writing this review.
Thus, the current implementation of CrossFire technology seems to be a good choice for a wealthy PC enthusiast. It is not going to be a sensation since the multi-GPU system market is in fact small, but it will surely occupy a niche of its own. Moreover, the upcoming RADEON X1900 family promises to push the performance bar of CrossFire systems even higher. NVIDIA should take care to reaffirm its current leadership and you will see everything in the practical tests of ATI’s new graphics cards on our site.
