AMD Radeon HD 7790 Review

Author: SKYMTL
Date: March 20, 2013
Product Name: HD 7790
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In a year which promises to be a slow one for new graphics cards, the HD 7790 is a breath of fresh air, even though it doesnít target the enthusiast demographic. At $149 this is very much a product which aims to close a perceived gap in AMDís lineup in more affordable price points. More importantly, it is supposed to introduce optimal performance levels at 1080P, todayís most-used resolution.

With their HD 7850 2GB retailing for about $199 and the lowly HD 7770 GHz Edition going for $119, AMD desperately needed a bridge solution between these two popular, yet miles apart cards. Thatís where the HD 7790 comes in. It is primarily being introduced as a way to finally challenge GTX 650 Tiís command of the $150 to $175 price point. However, considering NVIDIAís card has been around for the better part of 6 months now, it will take one hell of an effort in order to weed out such a heavily entrenched competitor.

At the heart of AMDís HD 7790 lies the 2.08 billion transistor Bonaire core which, like its predecessors, uses TSMCís 28nm manufacturing process. Rather than using a warmed-over Pitcairn design, this one utilizes brand new silicon and incorporates a number of minor revisions to the typical Graphics Core Next architecture in order to increase overall efficiency. However, make no mistake about it: Bonaire is still a GCN-based ASIC within the HD 7000-series so donít expect any over-the-top performance increases here.

Crammed onto this tiny 160mm≤ die is a pair of Geometry and asynchronous Compute Engines, a notable improvement over the single engine used within Cape Verde and more in-line with the layouts of higher-end Pitcairn and Tahiti cores. This allows the HD 7790 to process two primitives per clock and results in better tessellation performance and enhanced data throughput. It will also benefit DirectCompute performance, which has become quite important with the advent of compute-accelerated global illumination, AMDís TressFX within Tomb Raider and even Far Cry 3ís enhanced HDAO.

The Bonaire coreís 14 Compute Units each have the typical 64 cores totaling 896 Stream Processors along with 56 Texture Units and 16 ROPs. This means the HD 7790ís pixel fillrate remains at 16 GP/s, identical to what the HD 7770 GHz can achieve but the texture fillrate gets a significant 40% boost to 56 GT/s.

Looking at AMDís current lineup, it becomes evident that the yawning chasm between the HD 7850 and HD 7770 Ghz is finally being filled with a worthwhile product. The HD 7790 has nestled perfectly into its position but there will be some disappointment that it hasnít come equipped with a 2GB frame buffer. Supposedly, some board partners will be introducing 2GB SKUs but no one expects those products to perform all that much better at 1080P.

The feature set of this new card has also been significantly expanded. It comes with native support for both Crossfire and Eyefinity, two items which NVIDIA cards in this price range currently donít include.

AMD has also revealed some sad news: the venerable HD 7850 1GB is no longer being produced due to the GDDR5 memory modules it uses being discontinued. Its absence may be felt since it was a perfect gateway product for high performance at a low price point but the HD 7790 should take over much of the slack.

Another major change over previous designs in the mid to low end markets is the incorporation of memory controllers which support 6 Gbps GDDR5 modules. While the actual in-game performance increase may not be all that significant, a 10% bump in framerates certainly isnít anything to thumb your nose at either. The inclusion of these modules on a lower end card also points to how quickly the price of GDDR5 is dropping and it should only be a matter of time until it completely supplants GDDR3 throughout AMDís lineup.

One of Bonaireís main selling points is the design changes AMD has instituted in an effort to optimize power consumption while maximizing clock speeds. That mere 5W increase over a HD 7770 GHz Edition for significantly more performance doesnít come out of thin air.

Much like we detailed in the recent Richland APU Preview, AMDís new embedded on-die microcontroller is back for an encore presentation. It has the ability to accurately monitor temperatures, voltages and clock speeds along with their relation to ASIC TDP in an effort to determine a combination or factors to ensure optimal performance. These calculations and their respective clock and voltage changes are done at 10ms intervals which is a huge improvement over the previous generation designís ability to switch voltage rates at 50ms intervals.

In order to make the most out of what this controller brings to the table, AMD has instituted additional P-States within an enhanced version of PowerTune. As before, discrete DPM states dictate voltages and clock speeds based upon proximity to power limit but there are now more of them (eight versus four to be exact) so additional granularity can be inserted into the equation. The result is higher sustained engine clocks in all circumstances rather than select cases.

According to AMDís the HD 7790 wonít have any reference design and their board partners are being given freedom to experiment. But that hasnít necessarily led to a vast array of choices since (other than the reference clocked versions that is), we arenít really seeing all that much variety in clock speeds for factory overclocked editions. For the time being every one of them comes in at 1.075GHz with memory running at 6 Ghz or 6.4GHz. Sure there are plenty of different heatsink designs in the current stable but other than that, differentiation is hard to come by.

Sapphireís HD 7790 Dual-X OC is of the many examples of board partner cards and this one comes with a custom dual fan heatsink and measures about 8 ľĒ long, making it compatible with most cases on the market. It should also achieve some impressive cooling performance since Sapphire has equipped its heatsink with a large-scale aluminum fin array which is fed via a quartet of copper heatpipes. Pricing for this card should be about $159 or $10 more than the reference design which seems more than fair considering its higher clock speeds and custom design.

For the purposes of this review and in keeping with our commitment to never underclock to achieve reference speeds, in order to recreate a stock HD 7790, we flashed a reference BIOS to the Sapphire card. However, the Sapphire results have been left as-is and represent its true performance.

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