Report: AMD Radeon HD 6790 - BeHardware
>> Graphics cards

Written by Damien Triolet

Published on April 6, 2011


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Before the arrival of its new entry level graphics cards, AMD is bringing out the Radeon HD 6790, an additional mid-range model. Positioned exactly opposite the GeForce GTX 550 Ti, it should have a fairly straightforward performance advantage. It remains to be seen if following in the footsteps of the Radeon HD 5830 will truly make it a worthwhile model...

Barts LE
AMD has based development of the Radeon 6790 around a cut down version of Barts, the GPU used in the Radeon HD 6800s. The aim is of course to be able to give as many outlets as posssible for Barts GPUs which couldn’t make the grade as Radeon HD 6850s or 6870s. This LE version is scaled down just as the Cypress LE was for the Radeon HD 5830:

- 30% of processing units deactivated
- 50% of ROPs deactivated
- Higher TDP and core clock

As AMD has decoupled the ROPs from the memory controllers in its GPUs it can deactivate ROPs without affecting the memory controllers. The ROPs do however take up a lot of memory bandwidth and also represent an important pathway for this memory. Deactivating half of them therefore does have an impact on the GPU’s capacity to exploit fully the memory bandwidth made available by the 256 bit Barts bus.

To recycle a maximum of GPUs with significant current leakage, or which require higher GPU voltage, AMD and its partners have based the HD 6790 on an HD 6870 type design, better adapted to the potential load than the Radeon HD 6850. This results in a bigger card and of course higher energy consumption than the HD 6850, which however gives higher performance.

This Radeon HD 6790 therefore has a good few built-in disadvantages and won’t make much of an impact unless it gives very value. AMD will have to make a real effort given how complex the card’s design is. How does €130 look?

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Specifications, the card


In comparison to the Radeon HD 5770, the Radeon HD 6790 gives similar processing power (-1%) but with memory bandwidth up by 75%.

Note that AMD gives an “up to” clock for the GPU and memory on this Radeon HD 6790 but haven’t been able to tell us exactly what they mean by this, though of course this does lead you to think that there may well be more than the odd underclocked Radeon HD 6790 in stores after launch…

The reference Radeon HD 6790
For this test, AMD supplied us with a reference Radeon HD 6790:

This Radeon HD 6790 is, apart from the sticker on its cooler, in every way identical to the reference Radeon HD 6870. This means the card requires two 6-pin power connectors and measures 25cm. You can find more details in the Radeon HD 6870 test.

With respect to overclocking, we managed to take our test GPU from 840 to 950 MHz, a gain of 13%.

We should say that AMD wasn’t able to confirm whether this reference design would be available in stores or not as it looks as if most partners will be bringing out a customised model, derived from their own Radeon HD 6870s.

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Some technical details, the test

Some technical details
We wanted to compare the Radeon HD 6790 (Barts LE) to the Radeon HD 5770 (Juniper) and 6850 (Barts) in more detail on two specific points: tessellation and fillrate. Comparing tessellation allows us to observe the advantage given by the minor improvements introduced by AMD with the Barts GPU in comparison to Juniper, which is used in the Radeon HD 5770. Fillrate measurements reveal the impact of deactivating half of the ROPs.

To give us more exact measurements, we also clocked the Radeon HD 5770 and 6850 at the same GPU clocks and memory as the Radeon HD 6790.

Barts gives a 30% higher performance than Juniper in our test of triangle throughput with tessellation. The LE version (HD 6790) gives identical performance, at the same clock, as the standard version (HD 6850).

With half of its 32 ROPs deactivated, the Radeon HD 6790 clearly gives a lower pixel throughput than the Radeon HD 6850. It doesn’t however behave exactly like half a Radeon HD 6850, as the Radeon HD 5770 does with its 16 ROPs. It looks as if AMD might have deactivated not 50% but 75% of the parts of the ROPs charged with handling FP16 and FP32 formats.

With blending however, Barts LE partly benefits form its large bandwidth and is 28% more efficient than Juniper, translating into an advantage of 12% for the Radeon HD 6790 over the Radeon HD 5770.

The test
For this test we opted for three resolutions: 1680x1050 without and with MSAA 4x and 1920x1200 without MSAA, with the exception of Crysis Warhead and Far Cry 2 which were tested in more modes. We set the graphics options to high but not maximum in the most demanding games.

We have also decided to stop showing decimals in game performance results so as to make the graph more readable. We nevertheless note these values and use them when calculating the index. If you’re observant you’ll notice that the size of the bars also reflects this.

The Radeons and the GeForces were tested with texture filtering at the high quality setting. All the Radeons were tested with the Catalyst 11.4 preview 2 (8.84.2) driver. All the GeForces were tested with the 267.59 beta drivers, with the exception of Crysis 2 and Bulletstorm which were tested with the 270.51 beta drivers, again across all the cards. Note that the performance gains announced by NVIDIA with the 270.51 drivers should be compared with the 266.58s. Yet these optimisations, in terms of the games tested here, were already there in the 267.51 drivers.

Test configuration
Intel Core i7 980X (HT deactivated)
Asus Rampage III Extreme
6 GB DDR3 1333 Corsair
Windows 7 64 bits
Forceware 267.59 beta
Catalyst 11.4 preview2 (8.84.2)

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Energy consumption, noise

Energy consumption
We measured the energy consumption of the graphics card on its own. We took these readings at idle, in 3D Mark 06 and Furmark. Note that we use a version of Furmark that isn’t detected by the stress test energy consumption limitation mechanism put into place by NVIDIA in the GeForce GTX 500 drivers.

At idle, the GeForces have a small advantage over the Radeons. In load however, the Radeons draw much less than the Geforces at the same level of performance. The Radeon HD 6790 however gives a lower yield than the Radeon HD 6850 with higher energy consumption in load.

Noise levels
We place the cards in an Antec Sonata 3 casing and measure noise levels at idle and in load. The sonometer was placed 60 cm from the casing.

While the Radeon HD 6870 was pretty noisy, the Radeon HD 6790 is not. Though not quiet, it isn’t bad at all in load. Although both use the same cooling system, the Radeon HD 6790 no doubt benefits from the fact that it has less heat to deal with and better calibration of the blower speed to better contain noise levels.

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Starcraft 2

Starcraft 2

To test Starcraft 2, we launched a replay and measured performances following one player’s view.

All graphics settings were pushed to a maximum. The game doesn’t support antialiasing which is therefore activated in the control panels of the AMD and NVIDIA drivers. Patch 1.0.3 has been installed.

The GeForces do a bit better than the Radeons in this first test. In contrast to the GeForce GTX 550 Ti in comparison to the GeForce GTS 450, the Radeon HD 6790 struggles to take advantage of the additional memory bandwidth it has over the Radeon HD 5770.

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Mafia II

Mafia II

The Mafia II engine passes physics handling over to the NVIDIA PhysX libraries and takes advantage to offer high physics settings which can be partially accellerated by the GeForces.

To measure performances we used the built-in benchmarks and all graphics options were pushed to a maximum, first without activating PhysX effects accelerated by the GPU:

Here the Radeon HD 6790 only has a very slight advantage over the Radeon HD 5770 and GeForce GTX 550 Ti.

Next, we set all PhysX options to high:

With PhysX effects pushed to a maximum, performance levels dive. Note that they are in part limited by the CPU, as not all additional PhysX effects are accelerated. Of course the Radeons remain a long way behind.

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Bulletstorm is one of the best in the current crop of games. Although only in DirectX 9 mode, the rendering is pretty nice, based on version 3.5 of Unreal Engine.

All the graphics options were pushed to a max (high) and we measured performance with Fraps. Note that an issue with the games graphics engine brings about a significant dip in performance when the dimensions of the rendering area are not in multiples of 8 pixels. The performance readings at 1680x1050 were lower than at 1920x1200! To get around this problem, we created a customised resolution of 1680x1048 and noted a very significant gain, whatever the card used.

The Radeons do very well in this game, particularly with antialiasing.

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Crysis 2

Crysis 2

Crysis 2 uses a development of the Crysis Warhead engine optimised for efficiency. The game has few graphics options with just three main profiles: high, very high and extreme. For tests without antialiasing, we went for the very high mode and with 4x antialising we went for extreme, as it activates the 4x antialiasing filter. Note however that it also activates other graphics improvements.

We measured performance with Fraps in version 1.1 of the game.

The results gave us the following usual comparisons:
Radeon HD 6850 = GeForce GTX 460 1 GB
Radeon HD 5770 = GeForce GTX 550 Ti
Radeon HD 5750 = GeForce GTS 450

The Radeon HD 6790 does a little better than the Radeon HD 5770 and equals the GeForce GTX 460 SE when antialiasing is used.

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Crysis Warhead

Crysis Warhead

In spite of the release of Crysis 2, Crysis Warhead remains a reference in terms of graphics card performance. We tested it in its 1.1 hotfix version, at 64 bits and in ‘Gamer’ mode.

The Radeon HD 6790 is slightly behind the GeForce GTX 460 SE in this game.

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Far Cry 2

Far Cry 2

This version of Far Cry isn’t really a great development as Crytek made the first episode in any case. As the owner of the licence, Ubisoft handled its development, with Crytek working on Crysis. No easy thing to inherit the graphics revolution that accompanied Far Cry, but the Ubisoft teams have done pretty well, even if the graphics don’t go as far as those in Crysis. The game is also less resource heavy which is no bad thing. It has DirectX 10.1 support to improve the performance levels of compatible cards. We installed patch 1.02 and used the ultra high graphics setting.

The GeForces do particularly well with Far Cry 2 and the GeForce GTX 550 Ti takes the opportunity to move ahead of the Radeon HD 6790.

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H.A.W.X. is a flying action game. It uses a graphics engine that supports DirectX 10.1 to optimise results. Among the graphics effects it supports, note the presence of ambient occlusion that’s pushed to a max along with all other options. We used the built-in benchmark with patch 1.2 installed.

The Radeons suffer less than the GeForces at higher resolutions.

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The first game with DirectX 11, or more precisely Direct3D 11 support, we couldn’t not test BattleForge. An update added in September 2009 gave support for Microsoft’s new API.

Compute Shaders 5.0 are used by the developers to accellerate SSAO processing (ambient occlusion). Compared to standard implementation, via the pixel shaders, this technique allows more efficient use of the available processing power by saturating the texturing units less. BattleForge offers two SSAO levels: High and Very High. Only the second, called HDAO (High Definition AO), uses Compute Shaders 5.0.

We used the game’s built-in benchmark and installed the 1.2 build 304941 update.

The GeForces suffer here from their limited fillrate, which allows the Radeon HD 6790 to equal the performance of the GeForce GTX 460 1 GB. With antialising activated however, the GeForces come back into things as they’re limited at another level, which allows them to position themselves better opposite the Radeons.

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Civilization V

Civilization V

Pretty successful visually, Civilization V uses DirectX 11 to improve quality and optimise performance in the rendering of terrains thanks to tessellation and in implementing a special compression of textures thanks to the compute shaders. This compression allows it to retain the scenes of all the leaders in the memory. This second usage of DirectX 11 doesn’t concern us here however as we used the benchmark included on a game card. We zoom in slightly so as to reduce the CPU limitation which has a strong impact in this game.

All settings were pushed to a max and we measured performance with shadows and reflections. Patch 1.2 was installed.

The GeForces do very well here and the GTX 550 Ti gives a similar showing to the Radeon HD 6790.

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S.T.A.L.K.E.R. Call of Pripyat

S.T.A.L.K.E.R. Call of Pripyat

This new S.T.A.L.K.E.R. suite is based on a new development of the graphics engine which moves up to version 1.06.02 and supports Direct3D 11 which is used both to improve performance and quality, with the option to have more detailed light and shade as well as tessellation support.

High quality mode was used and we activated tessellation. The game doesn’t support 8x antialiasing. Our test scene is 50% outside and 50% inside and inside it is surrounded with several characters.

The Radeon HD 6790 is slightly down on the GeForce GTX 460 SE. Once again you can see that the Radeons suffer slightly less than the GeForces at higher resolutions.

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F1 2010

F1 2010

The latest Codemaster title, F1 2010 uses the same engine as DiRT 2 and supports DirectX 11 via patch 1.1 that we installed.

We pushed all the graphics options to a max and we used the game’s own test tool on the Spa-Rancorchamps circuit with a single F1.

In F1 2010, the Radeons are particularly comfortable and the Radeon HD 6790 finishes a little ahead of the GeForce GTX 460 1 GB.

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Metro 2033

Metro 2033
Probably the most demanding title right now, Metro 2033 forces all recent graphics cards to their knees. It supports GPU PhysX but only for the generation of particles during impacts, a rather discreet effect that we therefore didn’t activate during the tests. In DirectX 11 mode, performance is identical to DirectX 10 mode but with two additional options: tessellation for characters and a very advanced, very demanding depth of field feature.

We tested it in DirectX 11 mode, at a very high quality level and with tessellation activated, both with and without 4x MSAA.

The Radeon 6790 equals the GeForce GTX 460 SE here.

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Performance recap

Performance recap
Although individual game results are worth looking at, we have calculated a performance index based on all tests with the same weight for each game. Mafia II is included with the scores obtained without GPU PhysX effects.

We attributed an index of 100 to the GeForce GTX 460 1 GB at 1680x1050:

Hold the mouse over the graph to view the cards by performance at 1680x1050.

It’s interesting to see that AMD and NVIDIA are on an equal footing in several of the games: GeForce GTX 460 1 GB and Radeon HD 6850, GeForce GTS 450 and Radeon HD 5750… and GeForce GTX 550 Ti and Radeon HD 5770.

Another thing that comes out in this analysis is a trend we’ve noted with the GeForce 400s and 500s: they suffer a little less when antialiasing is enabled, but a little more at higher resolutions, which is explained by the reduced fillrate given by their internal architecture.

With a 10% performance advantage over the Radeon HD 5770, the Radeon HD 6790 is positioned between the GeForce GTX 550 Ti and GTX 460 SE. It is however further down on the Radeon HD 6850 which gives between 17% and 22% better performance, the biggest differences coming with antialiasing activated.

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With the Radeon HD 6790, AMD has exploited the weaknesses of what is an easy target: the GeForce GTX 550 Ti. While the Radeon HD 5770 already matched the GTX 550 Ti in terms of performance, it was obvious that the Radeon HD 6790 could only be a winner at €130. This was confirmed in practice with a 10% advantage for the Radeon in our tests.

AMD has nevertheless adopted the same approach in assembling the Radeon HD 6790 as it did with the much maligned Radeon HD 5830. It has a similar GPU to the one used in the Radeon HD 6800s but cut down both in terms of processing units and ROPs. The reduction in ROPs has a big impact on performance as it prevents the GPU from fully benefitting from the memory bus it has at its disposal.

Another similarity with the Radeon HD 5830 is that AMD based its design on the Radeon HD 6870 and not the Radeon HD 6850. This implies higher energy consumption and is justified in AMD’s desire to be able to recycle GPUs with big current leakage or which require higher voltage. Although this depends on the customised designs from AMD’s various partners, it does also imply less aggressive pricing.

At the end of the day, while the Radeon HD 6790 may have easily won its match up against the GeForce GTX 550 Ti, we do wonder what real benefits it brings. For gamers on a low budget we’d recommend either the Radeon HD 5770, more compact, with good energy economy and not too far behind in terms of performance, or the entry level Radeon HD 6850 or GeForce GTX 460 1 GB. To make it a better buy its price needs to come down to or equal the Radeon HD 5770, a direction Sapphire seems to be taking with the announcement of its model at €120…

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