Introducing AMD’s HD 6790

Today we are introducing the HD 6790, AMD’s midrange video card. It is a budget solution as it etails for what AMD calls a “hard pricing” of $149 and it is expected to perform well at 1920×1080 resolution.  Here it is in its most basic engineering sample form as AMD’s partners will decide even whether it will have one 6-pin PCIe connector or two.  It is designed to crush Nvidia’s recently released GTX 550 Ti in both price and performance.

AMD Graphics and Nvidia are locked in a perpetual battle to one up each other in what can only be described as a “graphics war”. Nvidia had issues with introducing their Fermi DX11 architecture and video cards and AMD beat them to the market by over six months with the first DX11 video cards. In April of last year, Nvidia launched their GTX 470 and GTX 480 which were criticized for being hot-running, power-hungry and loud although they offered somewhat higher performance than AMD’s HD 5870 and HD 5850. It appears that AMD actually believed that Fermi was unfixable.

However, a few months later, Nvidia’s midrange GTX 460 turned out to be a very successful reworking of GF100 Fermi into GF104 that scaled well, ran cool, had good thermal characteristics, overclocked well and no doubt ate into AMD’s then DX11 90% marketshare. To combat GTX 460, AMD released their HD 6000 series codenamed “Barts” with HD 6870 and HD 6850 being debuted this past October. This is not AMD’s high end, codenamed “Cayman”, which arrived at the end of last year, but rather their upper-midrange which was renamed from HD 58×0 series and is designed to take on and surpass the GTX 460 and all of its variants.  Both the AMD and the Nvidia GPUs are relatively complex and expensive to make so it stands to reason that lower-cost similarly-performing GPUs would be introduced to improve their margins.

We see that the HD 6970 and HD 6950 are designed to combat Nvidia’s brand new reworked GF110 which debuted since the HD 68×0 launch as thermally tamed and quiet-running GTX 580 and GTX 570 video cards which significantly surpass the HD 58×0 series’ performance. And of course Nvidia has upped the GTX 460 ante by releasing their GTX 560 TI a couple of months ago.  Finally, just over two weeks ago, Nvidia aimed for AMD’s bread and butter, the HD 5770 with their $150 “soft priced” GTX 550 Ti.

Today we see another ‘Barts’, the HD 6790, AMD cut-down GPU basically replacing their HD 5830; at least as a “spiritual successor” as it fill the same hole in AMD’s lineup between the HD 5770 and the HD 6850. This card has been designed to completely crush the GTX 550 Ti’s performance. The reference version is physically a long card the same size as the HD 6870.  Of course, AMD Graphics’ AiB partners are free to engineer this card as they see fit.  Here is a Powercolor version with only one 6-pin PCIe connector.

ABT was represented by this editor at AMD’s Press Day at the famous LA Exchange in October and saw AMD’s vision unfold further for us. Since we are going to focus on the HD 6790 ‘s performance in 28 games, we will only give you the barest outline of their 5 hour presentation which covered “Barts”, “Cayman” and “Antillies” graphics cards. We do see that the reason that they chose downtown Los Angeles is symbolic of their increasing commitment to the movie industry and they have partnered up with several Hollywood movie studios to increase productivity by using AMD hardware and know how. They also used the presentation to introduce their support for 3D in PC gaming and 3D for video playback.

AMD’s Press Event was called “Believe Your Eyes” and they laid out their vision for the world’s press. AMD feels that Fusion is uniquely suited to conquer the world and they stress the “firsts” they have accomplished, including being first to bring DX11 GPUs to market very quickly and successfully. They are quite proud of their marketshare and do not intend to allow Nvidia to easily make inroads.

AMD points out the advantages of their Eyefinity which now allows more displays to be driven off of a single card – up to six displays now with a hub adapter – rather than with Nvidia’s competing Surround solutions which require two similar video cards running in SLI to power 3 displays.

A rose by any other name …

Today, AMD Graphics is proud to introduce a new Barts, the HD 6970, with better performance, but still on the same 40 nm process as the Cypress 5000 series. With the release of the HD 6790, AMD wants to tackle 1920×1080 gaming with a $150 video card.  Here is another look at the engineering sample.  The connectors will be the same with the exception of a choice of either one or two 6-pin PCIe connectors.  Obviously two connectors are usually better for overclocking than one.

Here is AMD’s continuation of their video card strategy with the addition of the new HD 6990 at the very top and now the HD 6970 coming in above the HD 5700 series in performance but at a similar launch price:

Until now, we only saw changes to the upper midrange and at the high end. AMD continued the HD 5700 series until now; unchanged, as they evidently felt unchallenged by Nvidia’s GTS 450 which we reviewed here against HD 5750. In the above chart, we see the HD 5800 series diverge into 3 streams – the “Antilles” reviewed today, an “X2″ video card at the highest end as a successor to the current dual-GPU HD 5970; the “Cayman” as HD 6970 and HD 6950 which is using AMD’s fastest single GPU to succeed to surpass the Cypress HD 5870.

Here is the updated product strategy since AMD is responding to the newly released GTX 550 Ti which is faster than the HD 5770 and which we reviewed a few days ago here.  AMD’s partners have already renamed the OEM HD 5750/5770 into HD 6750/6770, so the “6790″ choice of a name is logical as it positions the new card as shown below.

Here is the Sapphire HD 6790.

This budget Barts retains all of the features of their bigger brothers, the HD 6850 and HD 6870 which we shall recap for you.  Here are the HD 6790′s specifications at a glance.

Frankly, on paper the HD 6790 looks to be no improvement at all over the HD 5770.  The only obvious advantage is the 256-bit memory bus which helps at higher resolutions.  However, AMD claims close to a 30% improvement over the HD 5770 from architectural improvements and other tweaks which should then put it solidly faster than the GTX 550 Ti which only edged out the HD 5770 overall.  We shall test it for you.   But first see what’s new in HD 6790 over the HD 5770.  We will soon see that it has more in common with HD 68×0 than HD 57×0.

What’s new in HD 6790?

Since “seeing is believing” is AMD’s theme for the 6000 series launch and it is all about the 3 “eyes”, we shall briefly cover them again here:

  • Eyedefinition
  • Eyefinity
  • Eyespeed

Under Eyedefinition, we see a further subdivision with more efficient tesselation; there is mention of a Barts tweaked engine, offering up to 2x the tessellation performance of the HD 58×0 GPUs – an area where AMD was perceived weak in comparison to Nvidia’s Fermi GPUs in heavily tessellated benchmarks and games. With Cayman we see the potential for a further increase of geometry performance and we also see mention of enhanced architecture for efficiently using GPU compute and for improvement and performance in games. We also note improvements in Anisotropic Filtering (AF) and new Anti-Aliasing modes – morphological AA and EQAA.

Eyespeed refers to GPU compute and to AMD’s “open initiative” approach to (everything and especially to) OpenCL, in contrast to Nvidia’s use of their own proprietary GPU language, CUDA. We see AMD partnering with Cyberlink, Arcsoft, Viewdle, Adobe, Microsoft and more companies (some of which are also Nvidia’s partners) to bring you, the end consumer, quality video processing and playback; and of course, UVD 3 accelerated decoding for 3D BluRay playback.

In our HD 68×0 launch article, we evaluated AMD’s claim of 35% better performance per mm over HD 58×0 and found that the HD 6870 is about equal in performance to HD 5850 overall. Not really too much has architecturally changed from Cypress except that Barts has up to 2x the performance of the tessellator in the HD 58×0 GPU. Here is the Barts GPU from AMD’s own presentation slide.

We were able to confirm that tessellation was superior in Barts over Cypress in Tessellation-heavy games and engines; in Lost Planet 2 and in Unigine’s Heaven, we saw the weaker-performing HD 6870 beat the generally faster HD 5870. We note that the HD 6790 still uses the Radeon’s VLIW5 core architecture. Overall efficiency will be improved over the HD 5570 Cypress GPU.

To see what it brings new, we note that the UVD engine has been updated; HDMI 1.4a is available for 3D Blu-ray and we see an improved Tesselator Engine. AMD now uses a second Ultra Threaded Dispatch Processor and an improved engine logic. We have noted in previous reviews, that Nvidia’s Fermi GPUs are faster in heavily tessellated scenes than competitive AMD Cypress GPUs. Well, now AMD claims a solid tessellation improvement over Cypress and HD 58×0 series and calls their method “tessellating the right way”.

In the case of Barts, it is supposed to be twice more efficient than the Cypress HD 5770 . Of course, we have to test this out to see what it means in a practical way for us gamers.

Morphological Adaptive AA

AMD’s new morphological anti-aliasing technique works as a post process effect. In other words, the GPU finishes rendering each frame as usual – but before presenting it to the display, it runs it through another shader pass to perform the filtering. This differs from traditional multi-sample and super-sample AA techniques where the filtering occurs during the rendering of each frame. In fact, this technique can eliminate aliasing for still images, though it’s intended to work better when in motion.

The filter works by first detecting high contrast edges with various pixel-sized patterns that are normally associated with aliasing, and assumes they should actually be straight lines that are not aligned to pixel edges. It then estimates the length and angle of the ideal line for each edge, and determines the proportional coverage by the lighter and darker color for each pixel along the edge. Finally it uses this coverage information to blend the colors for each pixel. All of this is actually being accomplished by the Catalyst drivers through a DirectCompute shader while the Local Data Share is used to keep adjacent pixels in memory for a low overall overhead. It will be interesting to see if AMD chooses to extend this morphological adaptive AA to the 5000 series as there is no reason it cannot be done, except perhaps to differentiate HD 6000 series from the current one.

AMD’s diagrams (below) should help to illustrate how this is accomplished.

Since the edge detection step requires frequent sampling and re-sampling of adjacent pixel colors, it offers a lot of opportunities for data re-use by using the LDS (Local Data Share) hardware to avoid redundant data fetches and to significantly improve performance.

Anisotropic Filtering (AF)

With the HD 5000 series, AMD brought genuine angle-independent filtering to gaming by putting an end to angle-dependent deficiencies. The AMD Radeon HD 6900 series continues to support fully angle invariant anisotropic filtering, and incorporates further improvements in LOD precision relative to the ATI Radeon HD 5000 Series. These image quality benefits come with no additional performance cost and remain enabled at all Texture Filtering Quality settings.

Architectural improvements

Like Cypress, all Barts, Cayman and Antilles GPUs are produced with the 40 nm process. AMD’s reference Cayman Radeon HD 6970 has 800 Stream Processors with its core operating at 840 MHz with 1GB of GDDR5 at 4.2 GHz (880/1050 MHz) on a 256-bit bus. There are 16 ROPs and 64 Texture units which means it was severely cut down from the HD 6850 so as not to compete with it performance-wise.

The HD 6790′s 256-bit bus is going to be a natural advantage over it’s rival the GTX 550 Ti’s 192-bit bus at higher resolutions.  In fact, Nvidia advertises their GTX 550 Ti as suited for 1680×1050 while AMD says their HD 6790 is perfect for 1080 resolutions

The HD 6790′s maximum load board power is 150 watts and its idle is 19 watts and it uses either a single 6-pin or else two 6-pin PCIe cables.  Here is the specification chart for the HD 6790.

We put all of our Radeon cards through their paces this week with the very latest WHQL drivers – Catalyst 11-2 except for HD 6790 and HD 5770 which used the latest preview drivers 11.4. This driver brought some good performance increases over the 11-2 WHQL drivers.  We used the release driver for the GTX 550 Ti  (267.59) and the latest WHQL 266.58 for the other Nvidia video cards.  We did not find a lot of performance increases when we partially tested the new 270 preview drivers from Nvidia and will leave that testing for later.

Is AMD’s HD 6790 worth $20 or so more than the GTX 550 Ti and what about the GTX 460?

We naturally want to know if the new AMD HD 6790 card is worth $150 as we compare it to the $150 GTX 550 Ti – now regularly discounted to $130 – and the $150 GTX 460; after all it is in the same price range.  We will have to do the testing and then you can answer these questions for yourself together with us in our conclusion.


The overclock on our HD 6790 can best be described as decent – from 840/1050 MHz to 940/1200MHz . It was not stable at 970 MHz and we had some issues with the unseasonably warm temperatures in our testing lab that went in excess of 80F. We only used CCC to set our Radeon overclocks and we did not increase the core voltage nor change the fan profile and we tested in a very warm environment that could be described as “Summer-like”.  We settled on only a moderate vRAM overclock as we did not get consistent performance improvement going much higher.

We used our Intel Core i7-920 at 3.8 GHz for this evaluation with turbo on (one core will hit 3.99GHz) so there was almost zero chance of any significant CPU bottlenecking. Read on to see our test bed and the games we used.



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Founder and Senior Editor of ABT.

2 Responses

  1. EP says:

    I still think that 6790 is the 5830 of its generation. Too many cuts leads to a crippled chip that exists only because AMD marketing wanted to sell you a chip that would otherwise be thrown in the trash bin because it had too many defects to pass as a 68xx/69xx. That might be good marketing but it’s not a good deal for the buyer.

    Beating the GTX 550 is an accomplishment, sure, but not much of one, since the 550 is such a garbage card to begin with.

    If you’ve got $150 to spend on a video card, just save up and buy a 6950 for $250. That extra $100 has a great deal of marginal value. As opposed to, say the $150 delta between a GTX 570 and 580, which is just like throwing money away.

    This generation of GPUs at 40 nm has been rather underwhelming on the whole. No true spiritual successor to the 8800 GT from either the red or green team. And with DX 11 adoption at a virtual trickle, thanks to the negative effects of consolization, it would appear that progress will be slow until the next-generation of consoles appears.

    Bring on 28 nm.

    On the bright side, another great review by ABT.

  2. Bo_Fox says:

    100% agreed with above comment!

    Well, I’d say that GTX 460 1GB is almost like the 8800GT of its time, but only if you could find one for $150 with rebates.

    Both companies are desperately trying to keep the prices up. Now, a $500 GTX 580 is starting to look a bit “mediocre” with some recent games like Metro 2033, Mafia 2, etc.. The price to pay for eye candy on the PC is rather high, and many games are console ports from consoles that are “several” years old, or a few PC generations behind.

    I find it to be really misleading when AMD claims that the 6790 has 256-bit memory when the sawed-off ROPs limit access to only half of the available bandwidth, as the card behaves exactly like as if it has 128-bit bus. For more on this, if you want to discuss on the forums here, I started a thread:
    I also believe that all Barts GPU’s are VLIW4-based like the rest of Northern Islands. It’s something else that appears to be in a dimly-lit area.. when one shines a candle in that area, something just doesn’t look right.

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