Review: AMD Radeon HD 7970

It has been roughly 18 months since AMD launched its last family of graphics processing units (GPUs) but we now finally have some hot new silicon from the California-based semiconductor company.

Codenamed Southern Islands (replacing last season’s Northern Islands family) the series initially consists of the Radeon HD 7970 and 7950 high-end cards, as well as the mid-range 7770 and 7750, all of which we’ve had the honour of testing in our labs this month. These will be followed by a mid-range HD 7800 and entry-level HD 7500 and 7600 series of cards, as well an enthusiast level HD 7990 (codenamed New Zealand, true story bro).

Our focus here however is squarely on the HD 7970, AMD’s current flagship GPU. Under the hood it has 2,048 stream processing units running at 925MHz built on a 28nm manufacturing process, and 3GB of GDDR5 memory running at 1375MHz (5.5GHz effective) over a 384-bit bus. Compared to the older HD 6970 which it replaces, the 7970 boasts over 33% more raw processing power (almost 3.8TFLOPS), 50% more memory bandwidth (264GB/s) and 50% more GDDR5 memory.

Physically the card measures 275mm long (including shroud), requires one 8 pin and one 6 pin PCI-E power connector (estimated power draw is 220W), has a 75mm blower fan with an aluminium heatsink sitting on a vapour chamber cooler, supports 3-way Crossfire and includes an HDMI, DVI and two mini-DisplayPort outputs. Retail units should also ship with HDMI-to-DVI and DisplayPort-to-DVI adapters, meaning one card can support up to three DVI monitors straight out of the box.

As with any launch of a new family of GPUs, there’s a whole swag of new functionality introduced as well. First and foremost, judging by the size of the sticker placed on the retail boxes at least, is the PCI Express 3.0 specification. If you have both a motherboard and video card which support PCI-E 3.0 then theoretically your video card can transfer up to twice as much data per second to and from the CPU and the rest of your system as the previous PCI-E 2.0 and 2.1 specifications.

I say theoretically because very few games even come close to saturating current PCI-E bandwidth capabilities, let alone require more bandwidth. It provides a level of future-proofing that may comfort some people however, and this isn’t to mention the potential benefits to general purpose computing on graphics processing units (GPGPU ) which we’ll look at shortly.

One possibly more tangible benefit to consumers is AMD’s new Zero Core Power technology. This feature creates two idle modes where there used to be only one. Firstly “regular idle” – the state where, for example, your computer is displaying your desktop and not sending any processing tasks to the GPU. This consumes about 15W of power.

This is a nice reduction in itself from the roughly 25W idle power usage of AMD’s previous generation of GPU. Secondly however is the new Zero Core Power mode, “long idle”, which is the state where the GPU is not even displaying an image at all – e.g. if you have your screen saver settings set to switch your monitor off but keep your PC running after a certain amount of inactivity.

In this mode, the GPU consumes a measly 3W, a figure so low that the card doesn’t even need to keep the fan spinning to keep cool. Same goes for unused Crossfire cards – if you have three cards hooked up but you are not doing any heavy GPU processing or gaming, then the fans on the two unused cards shut down – this will be a godsend for some noise-conscious gamers.

Moving on, the HD 7970 also introduces FastHDMI, an AMD technology which can push up to 4,000 x 2,000-pixel resolutions over an HDMI connection, as well as 120fps (60Hz per eye) full 1080P stereoscopic 3D image signals.

Also on the topic of displays: with a multi-monitor setup and AMD’s Catalyst 12.2 drivers you get Eyefinity 2.0, which has the ability to set custom desktop resolutions and relocate your Windows taskbar to any screen you want. On top of this the HD 7970 gives you Discrete Digital Multi-point Audio (DDMA); a fancy name for the ability to send different audio streams to separate monitors, useful for video-conferencing with multiple people.

Now, coming back to GPGPU – a big part of Southern Islands is what AMD calls Graphics Core Next (GCN). Essentially, GCN is the architecture which AMD built from the ground up starting with the HD 7000 series of video cards, to bring its GPGPU performance up to par with rival Nvidia.

GPGPU is a whole novel in itself, suffice to say however that things like digital image, audio and video processing (and k-NN nearest neighbour algorithms if you’re a real propellerhead) now have the potential to perform just as well on AMD hardware as they do on Nvidia hardware, once developers write software that can utilise the new architecture at least. The built-in H.264 Video Codec Engine is supposed to be on par with or better than Intel’s Quick Sync encoder as well.

Now for the all-important gaming metrics. To test the HD 7970 we put it up against the rest of the 7900 and 7700 series cards, as well as Nvidia’s closest competitor the GTX 580, plus an HD 6850 from AMD’s last generation of GPU. The test suite is a mix of old and new game titles, real life gaming scenarios and synthetic benchmarks.

As you can see from the results, the HD 7970 comes out about 20% better than Nvidia’s fastest single-GPU card, the GTX 580, in all test excepts for Trackmania Nations Forever, in which the Nvidia card absolutely dominates. This seems to have skewed the average FPS a little in the GTX 580’s favour however the HD 7970 still comes out on top overall. You pay for this privilege though, with the high ‘Dollar per FPS’ rating across the entire line-up.

What is not shown in the statistics is the noise and heat which the HD 7970 pumps out, neither of which is insignificant. No worse than the GTX 580, to be fair, so I feel this is endemic to high-end cards.

I also managed to have a quick go at overclocking the HD 7970 – core speed happily went from 925MHz to 1125MHz (the highest I could set it using the Catalyst Control Center) and memory speed was safe at 1500MHz (6GHz effective). With these settings the HD 7970 returned a 12% higher 3dMark11 Performance score – not bad for a free performance boost with minimal tinkering.

Overall, while we’re not totally blown away by this new card, the Radeon HD 7970 from AMD certainly doesn’t embarrass itself. It’s clearly the new king of the ring of single-GPU video cards. It brings an interesting bag of new tricks with it, too.