AMD Radeon HD 7790 Review - Sea Islands and Bonaire Make an Appearance
A New GPU with the Same DNA
When we talked with AMD recently about its leaked roadmap that insinuated that we would not see any new GPUs in 2013, they were adamant that other options would be made available to gamers but were coy about about saying when and to what degree. As it turns out, today marks the release of the Radeon HD 7790, a completely new piece of silicon under the Sea Islands designation, that uses the same GCN (Graphics Core Next) architecture as the HD 7000-series / Southern Islands GPUs with a handful of tweaks and advantages from improved clock boosting with PowerTune to faster default memory clocks.
To be clear, the Radeon HD 7790 is a completely new ASIC, not a rebranding of a currently available part, though the differences between the options are mostly in power routing and a reorganization of the GCN design found in Cape Verde and Pitcairn designs. The code name for this particular GPU is Bonaire and it is one of several upcoming updates to the HD 7000 cards.
Bonaire is built on the same 28nm TSMC process technology that all Southern Islands parts are built on and consists of 2.08 billion transistors in a 160 mm2 die. Compared to the HD 7800 (Pitcairn) GPU at 212 mm2 and HD 7700 (Cape Verde) at 120 mm2, the chip for the HD 7790 falls right in between. And while the die images above are likely not completely accurate, it definitely appears that AMD's engineers have reorganized the internals.
Bonaire is built with 14 CUs (compute units) for a total stream processor count of 896, which places it closer to the performance level of the HD 7850 (1024 SPs) than it does the HD 7770 (640 SPs). The new Sea Islands GPU includes the same dual tessellation engines of the higher end HD 7000s as well and a solid 128-bit memory bus that runs at 6.0 Gbps out the gate on the 1GB frame buffer. The new memory controller is completely reworked in Bonaire and allows for a total memory bandwidth of 96 GB/s in comparison to the 72 GB/s of the HD 7770 and peaking theoretical compute performance at 1.79 TFLOPS.
The GPU clock rate is set at 1.0 GHz, but there is more on that later.
By far the biggest change on the HD 7790 is the updated version of PowerTune that includes a more granular version of boost to allow for more steps in discrete clock speeds and GPU voltage levels. AMD promises that this version will allows for higher sustained engine clocks for more gaming performance while also being more power efficient, as well as being completely predictable.
The graphic above represents the current PowerTune with Boost found in the HD 7970 GHz Edition and the HD 7950 with Boost cards on the market today. The not-so-secret of that version of the technology was that there was truly only one additional step over the standard power management system.
Today's HD 7790 will be the first GPU to implement 8 discrete DPM states that the ASIC can switch between at a speed of 10ms. Not all of these new states lie between the "high state" and the "boost state" though in comparison to the previous graphic, leaving us some questions as to the effectiveness of this version of PowerTune in the long run. It does allow the GPU to use less power and use finer steps between the High and Boost states by not forcing the GPU to use one of only two voltage levels.
AMD did tell us that the "effective clock" will now be reported in the CCC as well as other overclocking and monitoring tools so we can actually see the clock rates change. I am going to be revisiting PowerTune and its Boost changes in the near future but the fact is that without overclocking, the HD 7790 very rarely even enters anything other than the Boost state while gaming - a fact that AMD confirmed to us during early meetings about the product.
Interestingly, AMD also changes the basics of the algorithm for boosting the clock speed, as it is now dependent on GPU load, current levels and a calculated, digital estimation of temperature. Still, AMD is confident that every buyer will get the same exact GPU performance and alterations across the entire line of HD 7790s, unlike the promises from NVIDIA of slight variances of clock speeds in tradeoff for higher "typical" clocks.
Again, more on this later - we don't yet have the right product to really test out AMD's updated technology.
Here is the comparison of the HD 7790 with the HD 7770 and HD 7750, though the HD 7850 statistics are left out. Obviously the HD 7790 is speced out better than the other HD 7700 parts, but the HD 7850 is only going to cost another $15-25 more than the new HD 7790 so it may be the more important comparison (it is included in our benchmarks).
Notice the 1.0 GHz clock rate listed here, without a designated "boost" clock. How can you have PowerTune with Boost and not list a boost clock? The truth is the GPU will basically ALWAYS be running at 1.0 GHz, the highest DPM state of the GPU. That is why I feel that the explanation of boost technology is kind of lost on this product - there is no variance in the speeds you will see during gaming.
For our testing AMD and Sapphire sent us a Dual-X overclocked model of the HD 7790, pushing the GPU clock rates up to 1.075 GHz and the memory speed from 6.0 GHz to 6.4 GHz - healthy boosts on both fronts.
The Radeon HD 7790 is fairly small card and only requires a single 6-pin ATX power connector to meet the TDP of 85 watts.
Front panels connections on the Sapphire card include a pair of DVI connections (one single, one dual link), a full size HDMI and a full size DisplayPort. This is easily one of the best output configurations we have seen on an AMD HD 7000 card and mirrors the combinations that the GTX 600s tend to use.
The back side of the board is pretty bare and it appears that Sapphire could have made this card even shorter if the needed to. Maybe we'll see some really small SFF options using this new GPU?
Finally, here is a slide of collected data on many of the partner cards releasing today or in the next week based on the HD 7790. All of them are overclocked on either the GPU or memory clock, with most of them on BOTH, so hunt around if you are looking to pick up one of these new cards.
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