AMD launches Radeon 7790: Meet the Xbox 720′s GPU
Today, AMD is launching the new Radeon 7790, a midrange GPU aimed at the $149 market segment. According to AMD, it’s taking this step because a price gap has opened between the HD 7770 at $110 and the HD 7850, which starts ast $179. The 7790 is based on an a new Graphics Core Next (GCN)-class core, codenamed Bonaire. Bonaire is built on the same 28nm process technology as AMD’s other GCN parts and it uses the same architecture. It’s also almost certainly the same GPU as what’s in the Xbox Durango. Before we hit that, let’s cover what’s new in the card in general, and why it’s a far more attractive option than the HD 7770. If we ignore the rebadges, AMD’s HD 7000 product family is based on three GPU designs — Tahiti (HD 7900), Pitcairn (HD 7800) and Cape Verde (HD 7700). The Cape Verde core is the smallest, with a max of 640 stream processors, a 128-bit memory interface, and a single primitive pipeline (maximum process rate of one primitive per clock). This cut-down design didn’t work very well; the HD 7770 was generally panned at launch, particularly in comparison to the HD 6850 . The HD 7790 should fix that problem. Tahiti, Pitcairn, and Bonaire use the top configuration, the HD 7770 uses the bottom. The Radeon 7790 combines the greater geometry power of Tahiti and Pitcairn with the smaller memory bus on Cape Verde. The end result looks like this: Performance benchmarks indicate that the Radeon 7790 is 20-40% faster than the HD 7770 and much better competition for the Nvidia GTX 650. AMD has made much of the fact that the 7790 supports SLI configurations and up to six displays (actual number of supported displays will depend on which connection options board vendors support). AMD has also improved its overclocking technology (PowerTune); the system introduced on Bonaire is programmed with eight potential states, rather than the four that previous HD 7000 cards offered. AMD expects that we’ll see 1GB and 2GB options but the company is leading with 1GB cards. How much this will matter to modern games is an open question — especially when the GPU uses a 128-bit memory bus. The card’s 96GB/s of memory bandwidth is impressive for a bus that small — the GDDR5 on the first round of cards is clocked at 6GHz and up — but it’s a bit pinched compared to the HD 7850. Those are the basics of the HD 7790 as a PC solution, so let’s switch gears and talk about the next generation Xbox.
First, there’s the question of why Bonaire exists in the first place. The gap AMD points to between the HD 7700 and HD 7800 families is real enough, but that’s the sort of hole that AMD would typically plug by scaling the HD 7800 down. Given the delays, financial problems, and layoffs AMD has suffered in the past 18 months, it’s ludicrous to think the company would invest in building a new GCN implementation just to hit a particular price point in a slightly more efficient manner. It’s no coincidence that Bonaire answers some of the questions we had after the Xbox Durango GPU leak early last month. According to VGLeaks’ data, Durango’s front end was capable of issuing up to two primitives per clock like Tahiti and Pitcairn, but the memory bandwidth figures pointed to a 128-bit bus. Now we have Bonaire — a 128-bit GPU that merges those two capabilities in a single part. Spinning a new GCN part for Microsoft allows for a smaller die, lower manufacturing costs, and explains why AMD CEO Rory Read calls AMD’s console SoC’s “semi-custom” designs. It makes no sense for AMD to build and launch another GCN part just to hit a market target — but it makes a lot of sense for a cash-strapped company to design a new GPU that can target multiple markets simultaneously. That said, the hypothesized Durango GPU isn’t a perfect match for the HD 7790. Durango has 12 CUs for a total of 768 cores instead of the 14 CUs (896 cores) that the HD 7790 has. Clock speeds are also lower, at an estimated 800MHz. The 102GB of bandwidth between Durango’s GPU and its 32MB ESRAM cache is a clean fit if we assume a 1600MHz cache clock and a 128-bit bus. Overall performance data on the 7790 is quite good, but price-wise, this card could clash with the HD 7850. At $149, 2GB cards based on Pitcairn are available for ~$180, and they offer significantly improved memory bandwidth as well as a modest increase in fill rate compared to the 7770/7790. The 7790 should compete nicely against Nvidia’s current Kepler lineup in that segment, though Team Green won’t leave this space empty for long if it needs to hit back. It would be nice to see a wider memory interface, but the HD 7790 delivers 20-40% more performance than the HD 7970 for a 35% increase in price ($110 as compared to $149). It’s a much better card than AMD’s previous offering in this space, and it should compare much more favorably to previous GPUs like the HD 6850. This is a better-balanced GPU, period. http://www.extremetech.com/gaming/151367-amd-launches-radeon-7790-meet-the-xbox-720s-gpu http://www.extremetech.com/gaming/151367-amd-launches-radeon-7790-meet-the-xbox-720s-gpu/2
AMD’s current stack
Examining the evidence
The Radeon 7790 anchor’s AMD’s low end
