AMD Radeon HD 7970: 28nm Tahiti GPU Review - HotHardware

AMD Radeon HD 7970: 28nm Tahiti GPU Review

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As we’ve mentioned, at the heart of AMD’s Radeon HD 7900 series graphics cards lies a totally new GPU codenamed Tahiti, which is based on a new architecture dubbed Graphics Core Next.

According to AMD, GCN was three years in the making and is designed to be scalable in ways AMD couldn't achieve before. The architecture is tuned for high graphics and compute performance and optimized for parallel and heterogeneous computing applications.


AMD Tahiti GPU w/ Graphics Core Next (GCN) Architecture

The cores in Tahiti have been completely redesigned from scratch. In its full configuration, the GPU features 2048 Stream Processors, arranged in 32 compute units, each with 64 vector units (4 x 16), and a 384-bit wide GDDR5 memory controller. The GPU has dual geometry engines and 8 render back ends than can process 32 color ROPs and 128 Z/Stencil ROPs per clock. The geometry engines and render back ends are also up to 50% more efficient than AMD’s older architectures. There is 768KB of read/write L2 cache, and L1 caches have been doubled over the previous generation as well. Not only is there more cache, but the caches have more bandwidth as well. In fact, AMD claims 2TB/s of bandwidth across all 32 caches on the chip, when operating at 925MHz.

The Tahiti GPU is manufactured using TSMC’s advanced 28nm process node and is comprised of a whopping 4.3 billion transistors, more than double the 2.1B transistors of the Cayman GPU used in the Radeon HD 6900 series. Dies size for the chip is 365mm2.

Graphics Core Next features a new instruction set, that’s not VLIW like previous generations and is more flexible and easier to program. The primary graphics pipeline and two compute pipelines can work independently of each other. Each compute unit can also execute instructions from multiple kernels simultaneously. The architecture is designed for increased instruction per clock per mm2 and is designed for high utilization, high throughput, and multi-tasking.


Radeon HD 6970 vs. 7970 Specification Comparison

As implemented on the Radeon HD 7970, the Tahiti GPU is clocked at 925MHz and offers up to 3.79TFLOPS of compute performance. There are 128 texture units (up from 96 in the Radeon HD 6900 series), which off a peak texture fillrate of 118.4GT/s and 32 ROPs; peak pixel fillrate is up slightly from the 6970 to 39.6GP/s.

Radeon HD 7970 boards will also feature 3GB of GDDR memory running at 1,375MHz, for an effective data rate of 5.5Gbps. The memory is attached to the GPU via a 384-bit wide memory bus, resulting in peak memory bandwidth of a 264GB/s, which is a huge leap over the 6970’s 176GB/s peak. Although the memory is clocked at a similar rate, the wider bus on the 7970 affords much more bandwidth. Board power is similar between the Radeon HD 7970 and 6970 at a peak of 250W.

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Wow thats crazy. MY 6950 still does the job right. I will just wait for the 8000 series.

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Dammnn...that's more than twice as powerful as my 3800. I need an upgrade. So bad.

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Great review Dave and Marco!!!!!!!!!!!!

I am stoked about this one. HH at it's finest here!!!

Can't wait to see what Nvidia will bring to the table in response.

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Good review. I knew 28nm would bring considerable improvements; I just have to wonder if it's able to gain a respectable overclock while still keeping the acoustics in check; oh if AMD let you have the card for longer!

Aside from that, this card looks nice. Actually makes my 6950 look meger in comparison; I can't help to imagine what NVIDIA's answer to AMD would be (probably more powerful but I doubt that NVIDIA would be able to release anything mindblowing on time after the Fermi debachery) but it just shows that the wait for 28nm is worth it just by looking at the charts alone. Just imagine the potential that can be had with this card and just imagine it further if someone were to put a third party cooler on it.

I'm not jumping on the bandwagon just yet; I actually plan to wait until Ivy Bridge is released and then buy the components one by one.

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who ever decided the word enthusiast would to the average person supersede hardcore isn't thinking with the ol noggin. sounds like a bird watcher. marketing ftw?

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Huh? Actually, I think it was coined in the press more than anything.

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How can Battlefield 3 not be included in the benchmarks? :/

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Because benchmarking the game can be pretty unreliable. You can use FRAPS but it's one of the tougher games to get consistent results with.

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The fact that you're test bed only pulled 375 watts at full load while providing that kind of performance is outstanding!

Could this system get by with a quality 500w PSU? If so, the need for monster kilowatt psus will virtually disappear (unless running multiple gpus).

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That's really what i'm curious about too - I've been holding out for these cards, have a 5850 that has served me well but is starting to really show its' age with the latest batch of games. Going dual-gpu card isn't an option for me and i'm limited to my current PSU.

Besides that, i think i may have been optimistic about this unveiling. As awesome as it is, I Was really hoping that this card would have nearly DOUBLE the performance of the 6950's... maybe with optimization and higher memory games such a beast will start to show its' utility.

Now i have to wait two more years for the 200 dollar version to come out hehe.

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