AMD Radeon HD 7870 2GB and HD 7850 2GB Pitcairn Review
Completing the Family
When we went to Austin, Texas to sit with AMD and learn about the Radeon HD 7900 series of cards for the first time, an interesting thing happened. While the official meeting was about the performance of the Radeon HD 7970 and HD 7950, when things started to settle several AMD employees couldn't help but discuss Cape Verde (7700-series) and Pitcairn (7800-series) GPUs. In particular, the HD 7800 cards were generating a lot of excitement internally as a spiritual follow up to the wildly successful HD 5800 and HD 5700 series of cards in terms of price and performance characteristics.
So while the Radeon HD 7970 and HD 7950 are being labeled as the world's fastest GPUs, and the Radeon HD 7700 is the fastest GPU for everyone, the HD 7800s are where many of our readers will look when upgrading their machines while staying within a budget.
Be sure to check out our video review posted here and then continue on to our full, written review for all the benchmarks and analysis!!!
AMD Pitcairn - the Radeon HD 7800 series GPU
To complete the family of Radeon HD 7000 series of GPUs (still pending the dual-GPU Radeon HD 7990), the Pitcairn GPU brings the same Graphics Core Next architecture we first saw in the HD 7900 into the $250-350 price rage. If you haven't read about the changes and updates in AMD's latest graphics architecture you should really stop by the first couple of pages of our HD 7970 review to get the necessary back story before moving on. Don't worry, I'll wait for you finish...
As I mentioned above, AMD really is hoping to duplicate the success of the Radeon HD 5800/5700 cards with the HD 7800 series. According to the Steam Hardware Survey from January the AMD Radeon HD 5800 series of cards make up 27% of the total DX11-capable hardware on users systems. That is pretty significant and simply put AMD as a company needs a runaway success like that once again.
The Pitcairn GPU that is the base for the HD 7870 and HD 7850 graphics cards is cut down from the Tahiti GPU and includes 20 Compute Units, 1280 stream processors, a 256-bit memory bus and quite a bit more. That is roughly 65% of the theoretical horsepower of the HD 7970 card found on the HD 7870 for about 65% of the cost.
Unlike the HD 7700 cards, the HD 7800s will keep the dual geometry engines, rasterizers and asynchronous compute engines. By keeping a nearly full-size 256-bit memory bus the HD 7800s should see much less memory performance penalty as well (5.5 Gbps versus 4.8 Gbps).
In our image above you can see a comparison of the three Southern Islands GPUs starting with the Tahiti (largest), going down to Pitcairn (middle) and completed with Cape Verde (smallest). Pitcairn has 2.8 billion transistors and is of course built on the same 28nm process technology that brings tremendous power benefits but apparently a lot of production and inventory questions as well. The die size as reported by AMD is 212 mm2.
AMD is definitely trying to capture that large audience that bought into the Radeon HD 5800 cards - these types of comparisons will be showing up EVERYWHERE and try to illustrate the architecture and performance differences you would see by moving from Evergreen to Southern Islands.
There is a software change that will come with the HD 7800 release: MLAA 2.0. This update will be available with the Catalyst 12.3 beta driver and then all drivers after that. The good news is that this performance and quality improvement will be backwards compatible with all the 7000-series and 6000-series cards from AMD.
The Radeon HD 7870 GHz Edition (pictured) above will retail for somewhere around $350 and will use the full Pitcairn GPU with 1280 stream processors. As the suffix to the card indicates the reference clock of this part is 1000 MHz with a memory clock of 1200 MHz running on a full 2GB of frame buffer. The typical board power for the HD 7870 is only 175 watts though we will see that it can easily prove itself more power efficient than anything NVIDIA currently has on the market.
Even though the reference clock is 1 GHz, AMD wants everyone to know that these cards should be able to overclock even higher with very little additional effort. The graph above shows the Radeon HD 7870 running at 1200 MHz core clock and 1375 MHz memory clock.
Here are the base specs for the Radeon HD 7850, planned to be sold at $250 or so, that includes 16 Compute Units and 1024 stream processors. The clock speeds are quite a bit lower at 860 MHz core though it does keep the same 1200 MHz memory clock with the same 2GB frame buffer. Typical power usage drops to around 130 watts here.
I really feel that the 2GB frame buffer on cards as low as $249 is a big differentiating feature between the Radeon HD 7800/7900 cards and current lineup of NVIDIA GeForce offerings. The high end GTX 580 only has 1.5GB of memory unless you purchase a special edition model and with cards like the GTX 560 Ti only getting 1GB, there are some interesting issues that crop up in games like Battlefield 3.
In a similar fashion to the overclocking capability of the HD 7870, AMD was touting the overclocking capability of the HD 7850 as well, hitting as high as 975 MHz core. In my testing we actually saw the HD 7850 hit as high as 1050 MHz!
Here we have the detailed table of specifications on these two new cards so you see them side by side. While the Radeon HD 7870 will have 80 texture units the HD 7850 will drop to 64 of them; both cards have 32 ROPs though for render backend performance.
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