The AMD Radeon HD 6990 graphics card, code-named Antilles, officially saw the light of day on March 8, 2011. The former flagship was replaced by a monster with two GPUs made using the same 40nm technology as the 5970 model chip. AMD had to make extraordinary decisions to improve the performance of the video card.
How did 6990 come about?
With the Radeon HD 5970, the manufacturer was in an interesting position. By launching the 5000 series about 6 months earlier than the 400th NVIDIA series, AMD has demonstrated leadership in new product launches. NVIDIA never responded to the 5970, despite the fact that the dual-processor version is fully compatible with its 400th series. The 5970th model was the undisputed queen of video cards - there was nothing more powerful then. Thus, given the lack of direct competition, the question of how AMD will replace its flagship was of great interest.
The Radeon HD 6990, AMD's new highest-performance card, was based on two Cayman GPUs (VLIW4) installed on a single PCB. The processor clock speed was reduced to 830 MHz, and the GDDR5 frequency - to 1250 MHz (which corresponds to a data transfer rate of 5 GHz). The card came with 4 GB of RAM, which, due to CrossFire’s internal settings, was reduced to an effective capacity of 2 GB, which corresponded to other models of the 6900 series.
Starting with the 5970th model, the calculated power and laws of physics began to limit AMD’s capabilities in what the company could do with a card with two GPUs. Unlike the 4870X2, the clock speed was not high enough to match the HD 5870 pair . In the 5970th model, the processor was slower by 125 MHz, and the data transfer rate of 800 MHz was 200 MHz behind. In practice, this reduced the performance of the 5970 to the level of 5850CF.
The AMD Radeon HD 6990 also lagged behind, but not so much. The frequency of 830 MHz was only 50 MHz (5.5%) less than that of 6970, and 5-GHz memory - at 500 MHz (9%). As a result, at basic settings, 6990 was closer to the dual 6970 than 5970 was to 5870.
6990 processors are fully functional. All 1536 shaders and 32 ROPs are involved in them, so the only difference from 6970 is the clock frequency.
Compared to 5970, the official standby power has dropped to 37 watts thanks to better Cayman power management. But under load, the power consumption of the board is 375 watts, and, as in the case of 5970, this is not the limit. If at base frequencies 5970 remained in the PCI-Express specifications by default, 6990 does not even try to do it.
The release of Radeon HD 6990 completed the upgrade of AMD's high-performance product line, which included 6970, 6950 2 GB and 6950 1 GB cards. At the same time, the average price for 6970 was less than half the cost of 6990, and installing 6970 CrossFire was cheaper.
Design
If you recall the 5970, then there were several areas in which AMD cards needed improvement. If the cooler system was enough to overclock the processor to the frequencies and voltages of the 5870th model, then the VRM cooling was insufficient, which led to the launch of the thermal protection mechanism. And although everything was within the framework of safety rules, with long-term operation it was inconvenient.
The design of the HD 6990 is very similar to an engineering solution to this problem. In addition, AMD not only eliminated the shortcomings of 5970, but also had to cope with an even greater load. The result was significantly different from its predecessor.
If you compare the HD 6990 vs 5970, the first card is a bit shorter. This is because the 6000 series case has a more angular shape than the beveled design of the 5000 series. As a result, the card has the same dimensions of the printed circuit board (292 mm) and 305 mm case (309 mm in 5970). This means that 6990, despite the increased cooling requirements, occupies almost the same space.
Cooler
The most attention in the video card is attracted by the cooling system. The traditional cooler of the 5970th model had its strengths and weaknesses. He tolerated the ability of the case to remove hot air, but the processor, which was located closer to the fan, cooled better. The problem was the cooling of the voltage control modules, since they overheated long before the fan began to increase speed.
To fix this and provide even greater heat transfer, I had to abandon the rear location of the fan. It was replaced by a design that was already used in third-party cards, such as Asus ARES 5870X2: a central cooler with processors on both sides. The difference was significant. If the rear fan vented most of the hot air outside the PC case, then the central one divides the card in half: the heat of one set of GPUs and supporting chips is displayed outside, and the second - inside the computer. Since the structure remained closed, hot air escapes from the front and back, and cold air is drawn in the middle of the card.
Changing the design of the cooler led to the replacement of a single radiator of the 5970th model with segmented one. 6990 is more like 2 separate graphics cards using one board than one with two GPUs. Each heatsink is connected to the processor through its own evaporator, as a result of which the chip cooling systems are completely isolated from each other.
Thermal grease between GPUs and evaporators has been replaced. Instead of the traditional composition, AMD used a phase-change material that melts and hardens depending on the temperature. This was not something revolutionary, but it was not always applied. As a result, thermal conductivity improved by 8%.
The voltage adjustment modules have been relocated to correct the limited cooling capabilities of the 5970 model. They were located in the center of the board so that they were cooled earlier than the GPUs or RAM modules. This not only reduced their heating, but also responded to higher energy consumption. The cooling of VRMs has become even more important. As with the 6970, voltage regulation is provided by Volterra's MOSFETs and controllers.
The 5970th model was developed with a view to dissipating 400 watts of heat, and the HD 6990 - at 450 watts. In practice, the capabilities of the latter approach 500 watts. The removal and dissipation of such an amount of energy in 1180 cm 3 of space are admirable.
Food
The Radeon HD 6990 graphics card receives power both directly through the standard PCIe bus, and through 2 8-pin PCIe slots. Thus, the power consumption limit is 150 + 150 + 75 = 375 watts. As with the 5970, any increase in consumption leads to an excess of PCIe's external power capabilities. 375 watts of power goes beyond this specification. Meanwhile, as in the case of 5970, at the base clock frequency, the GPUs receive a reduced voltage to match the target power. For Cayman chips to work at 830 MHz, a voltage of 1.12 V is used.
Power has a big impact on GPU performance, since an increase in 6990 performance compared to 5970 required AMD to change both the power consumption of the card and the introduction of PowerTune power management system. The latter was first introduced in the 6900 series in December 2010. By limiting power consumption within the set value and restraining performance when it was exceeded, AMD was able to increase the clock speed without worrying about security when launching applications such as FurMark. The search for balance is complicated by the fact that setting the frequency too high for a certain power along with the performance limitation is counterproductive and leads to inconsistent operation, and too low a frequency leaves the card's potential unrealized.
The increase in power consumption and the simultaneous introduction of PowerTune allowed AMD to increase the GPU clock speed in the same way as in the case of the 5970. The Cayman architecture is faster than Cypress, but the advantage of 105 MHz makes the difference really noticeable. At default settings, PowerTune seems to be tuned to 6990 almost the same as to 6970: FurMark is very slow, and Metro is experiencing slight delays. The usual PowerTune tuning range is available within +/- 20%, which allows you to set the power consumption limit to 300-450 watts.
According to user reviews, PowerTune lacks a dynamic limit based on the use of CrossFire. Perhaps the biggest drawback of dual-GPU cards is that they cannot compare with single-chip ones, since their clock speeds are kept low to limit the total power consumption. If one GPU could use the standard 880 MHz when the second processor is idle, this would make it possible to achieve the level of high-end single-chip cards in tasks that do not benefit from CrossFire, such as window games, emulators, GPGPU applications and games without profile CF.
As in the case of 5970 and 2 GB 5870, the HD 6990 is equipped with 16 RAM chips, 8 per GPU. One half of them is on the front of the circuit board, and the other is on the back. The rear panel provides protection and heat removal from the RAM located there. One of the few differences from 6970 is the use of 5 GHz instead of 6 GHz. This means that the base clock frequency of the RAM card already corresponds to the nominal. In the technical description of HD 6990, it is noted that 6-GHz RAM is designed for 1.6 V, and 5-GHz - 1.5 V. Thus, the difference boils down to several factors: lower RAM power consumption, lower costs and operational problems at frequencies above 5 GHz.
Connectivity options
There have also been changes in this area. Since Cayman GPUs can only control one dual-channel DVI monitor, AMD got rid of the 2nd SL-DVI port and HDMI port in favor of additional mini-DisplayPort. If all Cayman GPUs (and Cypress / 5800 before) can serve up to 6 monitors, the only way to do this within 1 slot is to place either 6 mini-DP ports (like Eyefinity-6), or using an MST hub. 6990 is an example of a compromise between these approaches. Eyefinity-6 requires an expensive adapter between DP and DLI-DVI to connect a single DL-DVI monitor, and the 5970-like 2 x DVI + mini-DP design does not allow the use of 6 monitors even with MST hubs. The end result is 1 DL-DVI port for legacy 2560x1600 / 2560x1440 monitors and another 4 mini-DP for new displays. This allows you to control 5 monitors directly and 6 monitors with an MST hub.
As with the 5870E6, adapters are needed to minimize the use of DisplayPort. All 6990 were equipped with passive adapters SL-DVI and HDMI and active SL-DVI. Built-in connectivity and adapters allow you to create almost any combination, including the popular configuration of 3 Eyefinity 1080p monitors.
Heat dissipation
Changing the cooling scheme, power consumption and heat dissipation required not only a different card length and power supply concept, but also additional attention to the system. A number of high-end models before this could not cope with the removal of hot air, but there was nothing like the HD 6990. In particular, no 12-inch card removed more than 185 watts of heat directly from its rear. Most of the designs were much more open and directed air flows in all directions.
The critical point of the HD 6990 is the removal of a large volume of hot air into the PC case. If the 5970th model forgave a lot in this regard, then the 6990th was not like that. A video card needs a case with a large air flow, especially if it is planned to disperse it, and nothing valuable should be directly behind it.
Users measured the temperature of the hard drive located directly behind 6990. At the base frequency, it was 37 ° C, and during overclocking it reached 40 ° C. For the 5970 card, the temperature drops to 31 ° C, and for a pair of 6970s in CrossFire with a 120 mm fan, it reaches 27 ° C. Thus, the penalty for having a dual air outlet is 6 ° C compared to 5970 and 10 ° C compared to a pair of shorter 6970. This suggests that placing a hard drive (or any other component) behind the video card is undesirable. Since in most cases you can find free hard drive bays in other places, it is better to rearrange your HDD as far as possible from 6990.
You can go even further and turn the nearest frontal intake into an outlet. In some cases, the inlet is located on the front panel of the case and roughly corresponds to the PEG 1 socket. If you use it to remove heat, this will allow it to dissipate much more efficiently. Perhaps this is precisely what the manufacturer was counting on when creating such a design.
Ultimately, the specifications of the AMD Radeon HD 6990 are not comparable to what it was before. Its large power consumption and dual exhaust cooler require a more careful attitude to cooling than any other card with two GPUs.
Computing power
Due to the architectural changes that AMD made during the transition to the 6000 series, especially in terms of computing performance, the performance of the Radeon HD 6990 could improve. However, the design with two GPUs did not give much advantage.
To evaluate changes, users used Civilization V, which uses DirectCompute to quickly transform textures. The game includes a test that checks the speed of the texture deployment algorithm needed for one of the main scenes.
Civilization V DirectCompute scales slightly with CrossFire. This leads to the fact that AMD Radeon HD 6990 4GB is ahead of 6970, but the Cayman architecture still looks unoptimized. The 5970 leads with a 10% advantage even at a lower clock speed. NVIDIA and its Fermi architecture are far ahead of the 6990 even without the advantage of SLI scaling.
Another GPU benchmark is SmallLuxGPU. The LuxRender application implements the full ray tracing mechanism in OpenCL, which allowed the process to be completely transferred to the GPU. SmallLuxGPU does not have CrossFire scaling, so this test deals with the performance of the first processor and shader / calculator. At standard clock frequencies, this leads to the 6990 being slightly behind 6970, but in overclocked state it is in perfect parity with it. Unfortunately for AMD, this is a test in which NVIDIA's focus on computing performance really paid off. Even with no CF scaling, the three times cheaper cheaper GTX 560 Ti card outperforms the AMD HD 6990.
Ultimately, in most personal computers, the advantage of having multiple GPU cores remained unrealized. As a result, 6990 was the best game card, but not a card for intensive computing.
Overclocking options
In the 6900 series, a BIOS selection switch appeared, which allowed users to safely overwrite BIOS cards, having in reserve a backup for work. In the 6990, this concept has been preserved in a modified form to provide unique overclocking needs. The switch remains, but serves to control the performance of the video card. In position 2, a write-protected BIOS is used, which sets the base clock frequency of 830 MHz and a standard core voltage of 1.12 V. In position 1, it is possible to change the BIOS, and the card starts up at the same main speeds and voltages as the 6970th models: 880 MHz and 1.175 V. The frequency of RAM remains unchanged at 5 GHz.
Test results
Comparison of the characteristics of the HD 6990 vs GTX 1050 Ti suggests that the performance of the AMD card as a whole should be higher. The bandwidth of the first is 179% higher - 320,000 GB / s versus 114,688 GB / s. In addition, the 6990th model performs anisotropic filtering 157% faster - 159360 versus 61920 Mtexels / s. Also, the AMD video card is significantly (29%) ahead of the competing model in full-screen anti-aliasing speed - 53120 versus 41280 MP / s. However, in the 3DMark Fire Strike 6990 test, it lags behind by 33%, gaining 5,820 points versus 7750 for the GTX 1050 Ti.
In BattleForge with maximum quality and 2560r resolution, the card provides a frame rate of 99.6 fps, inferior to 6970CF 9 fps and GeForce GTX 580SLI (125 fps).
With the release of 6990, for the first time, it was possible to launch the maximum Crysis settings with an acceptable frame rate on a single card. The model provides an acceptable 42.8 fps for a resolution of 2560 x 1600. Gaming settings allow you to play with a comfortable frequency of 64 fps.
Power and temperature
This is an area where AMD has traditionally had an advantage, as the strategy of small crystals led to less gluttonous and cooler processors compared to direct analogs of NVIDIA. Dual GPU cards, such as 6990, have the advantages of lower power consumption, but the heating temperature and noise are always unpredictable.
AMD continued to use one reference voltage in its cards. It plays a big role, as the PowerTune profile is calibrated to one specific value. In standby mode, the voltage is 0.9 V, under load - 1.12 V (for 6970 - 1.175 V).
In standby mode, the characteristics of HD 6990 are the same as in other models of the 6900 series - the processor runs at 0.9 V. Under load at the base clock frequency, it increases to 1.12 V, which largely explains why the card uses less energy than its performance level requires. When overclocking to 880 MHz, the voltage rises to 1.17 V, like 6970. Power consumption and heat dissipation increase accordingly, which is exacerbated by the fact that PowerTune is not used here.
The idle power of 6990 is consistent with the rest of the series. 171 watts corresponds to 6970CF, but compared to 5970 the card has a 9-watt advantage.
The load in Crysis gives the first indication that only the target energy consumption cannot be used to predict the total energy consumption. At 375 watts of rated power, the 6990 model should consume less than 2x200 watts of the 6950CF, but in practice the 6950CF consumes 21 watts less. This is partly due to a higher processor load, which allows for a higher frame rate, but this does not fully explain the discrepancy. Compared to 5970, the power of 6990 is much higher than the target. The 113-watt gap exceeds the 75-watt difference. Obviously, 6990 needs more nutrition than 5970.
Acceleration significantly increases energy consumption, this time up to 544 watts. This is better than the 6970CF due to some performance loss. It should be borne in mind that more than 400 watts are scattered from one card, which is fraught with consequences.
The FurMark test reveals PowerTune limitations, which are a determining factor for the 6900 series. Even with the restriction on for all three cards, the 6900 375-watt 6990 consumes 41 W more than 2x200 W 6950CF, and 51 W more than 6970CF. The power consumption of 6990 is proportional to the higher card performance compared to other models of the 6900 series.
As for the overclocked Radeon HD 6990 4GB without PowerTune, the card can withstand loads in terms of energy and heat consumption. 684 watts is significantly higher than 6970 without PowerTune and is close to 570/580 in SLI. It is difficult to measure the power consumption exclusively of a video card, but based on user data, you can be sure that 6990 consumes at least 500 watts, and this is one card with one fan that dissipates all the heat. The air exhaust from the front and rear ends of the case at the same time looks really good.
Along with improving the target power in the 6900 series, the AMD double-sided cooler, compared to the 5970, claims to be idle temperature. At 46 ° C, 6990 is warmer than other cards, but not too much (the XFX HD 6990 modification heats up to 51 ° C in standby mode), and this temperature is 7 ° C higher than that of 5970, which should fight against the fact that the second the processor is cooled by already heated air. The 6900 pair in CF is more efficient than the dual-output cooler.
The 5970th model warmed up more than the 5870CF, but the 6990 changed this trend. At the base clock speed, the processor is 2 ° C cooler than the 6970CF, which starts in a “bad” configuration when the cards are located directly next to each other. A heating temperature of 86 ° C is reasonable. Even an overclocked graphics card is only 2 degrees hotter. The heating temperatures of the XFX HD 6990, for example, under load at base and higher frequencies are 78 and 88 ° C, respectively.
The FurMark test does not significantly change the picture. If something improves the situation a bit, it's PowerTune, which holds the 6990 in mid-range positions. Acceleration, however, is a completely different matter. Without PowerTune, which controls power consumption, with a power consumption of 681 W, the card temperature reaches 94 ° C. The difference is only 5 ° C, but this is the limit of what users are willing to allow. About further acceleration is out of the question.
Noise
The card has a problem with the volume of the fan, which must be fought. In idle mode, there is nothing surprising. 44.9 dB louder than the average card, presumably due to a dual-output cooler.
If the Radeon HD 5970 is loud under load and the GTX 580 SLI is very loud, then they work quietly compared to 6990. The laws of physics cannot be fooled, and at some point, all smart engineering decisions are not able to compensate for the need for a large air flow dissipating 375 watts of heat. With 70.2 dB and 77.3 dB when overclocked, 6990 is an extremely loud card. And although games do not increase the fan volume as it does during the FurMark test, the cooler works noticeably louder than all other models. Ideally, 6990 requires good airflow and good sound insulation, but the former makes the latter difficult. Water cooling 6990 will cost a weight of gold.
Finally
The collaboration of 2 Cayman GPUs on the same board undoubtedly provided the HD 6990 graphics card with the title of the fastest on the market. At the same time, there has always been and will be a difference between cards with one and two GPUs. If the former pose a threat to the latter, then the opposite is unlikely.
In 2009, a similar question arose: which is better - 5970 or two 5850 in CrossFire, considering that they were almost identical in performance? The answer was that CrossFire is the best solution if you have a power supply with 4 easily accessible PCIe slots. In the case of 6990, the answer is even more direct. With some exceptions (for example, the lack of free space for 2 cards or in the HD 6990 x2 configuration), 6990 is inferior to the pair in CrossFire.
There are many reasons for this. The characteristics of the HD 6990 are so close to the 6950CF that on average at 2560 they are identical. Only in Bad Company 2 and Stalker games, the advantage of 6990 is noticeable, which is lost in Civilization V or DIRT 2. Meanwhile, the 6950CF heats up less, is significantly quieter, consumes less power and does not have such driver problems as the HD 6990. And finally, the 6950CF is cheaper : the price for two video cards was 3/4 of the cost of one double. Similarly, a pair of 6970s is cheaper and at a resolution of 2560 provides about 8% better performance and quieter operation.
At the time of release, the specifications of the HD 6990 x2 (Quad-CrossFire) made it possible to turn a blind eye to noise and high power consumption. This required installation on a motherboard with a gap of 3 slots, but the configuration was quite real.
The last excuse for buying a video card was the need for a system of 5 Eyefinity monitors, which along with 6990 only supported 5870.