The current generation AMD GPU series collectivelly known as "Southern Islands" were released over a year ago, with the beginning of its rollout in January 2012. Sixteen months later, the Radeon HD 7000 series is still very much relevant, as AMD continues to release new models under the same GPU family.

The Radeon HD 7790 released last month it’s a product most gamers have the potential to enjoy considering its $150 price tag. The HD 7790 took the chip count for the series to 10 distinct 28nm GPUs. Today AMD has a wide range of prices covered starting at $100 with the Radeon HD 7750 up to $450 with the 7970 GHz Edition.


Those able and wanting to spend in excess of $450 on a single graphics card need to look in Nvidia’s direction at either the GeForce GTX 690 or the mighty GTX Titan, both extravagant $1000 options. Alternatively, if you can support multiple graphics cards, which let's be honest most gaming systems can, then a pair of Radeon HD 7970 GHz Edition graphics cards should work nicely (well, kind of).

Still AMD feels they need to offer an ultra-expensive graphics card as well and therefore today they are releasing the Radeon HD 7990. Although it's been over a year since they launched the Radeon HD 7970, we are just getting an official dual-GPU version, in truth they have been around for some time.


Products such as the PowerColor Devil 13 HD 7990 6GB, HIS Radeon HD 7970 6GB IceQ X2 and Asus ROG Ares II have been doing the rounds for quite a while now. So while the release of an official Radeon HD 7990 might not be radically new, it does mean a few things. For one, pricing will be unified, as will the specifications and features. Most importantly availability and actual driver support, making it much easier for cashed up gamers to get their hands on one.

The Radeon HD 7990 is very similar to the 6990 and the 5970 before it (ohh, and the 4870 X2 before that) in the sense that it's basically a pair of flagship GPUs from its respective generation stuck to the same extra long PCB.

In the case of the Radeon HD 7990 it takes a pair of 7970 GPUs with overclocked cores (from 925MHz to 1000MHz), while boosting the GDDR5 memory from 1375MHz to 1500MHz. These clock speeds happen to match the 7970 GHz Edition, though the 7990 doesn’t feature a Boost clock, so we feel the GPUs are better compared to the standard 7970.

Radeon HD 7990 in Detail

Here are some figures that AMD is throwing around to describe the Radeon HD 7990: 8.6 billion transistors, 4096 stream processors, 8.2 TFLOPS computer power, 6GB GDDR5 and 576GB/s memory bandwidth.

But, of course, as a dual-GPU graphics card those figures are not nearly as impressive as they might otherwise be if we were talking about a single GPU solution. 8.2 TFLOPS of computer power is nothing to be sneezed at either, so we will be keen to see how the 7990 handles itself shortly.

The Radeon HD 7990 is a monstrous graphics card measuring 30cm long (12 in), making it 3cm longer than the 7970 GHz Edition.

The GPU core is clocked at 1000MHz, 8% higher than the HD 7970, while the memory is clocked 9% higher at 1500MHz (6.0GHz DDR). Pairing that frequency with a 384-bit memory bus gives the HD 7990 a theoretical bandwidth of 288GB/s per GPU, for a whopping 576GB/s total.


Like the Radeon HD 7970 which comes loaded with a generous 3GB memory buffer, the 7990 allocates 3GB to each GPU for a total card capacity of 6GB.

We've found that when using multi-monitor setups at extreme resolutions, the larger buffer of AMD cards provide a significant advantage over Nvidia's, which are limited to 2GB for the most part. That said, the new GeForce GTX Titan does boast a 6GB memory buffer for a single GPU.

The core configuration, or as we should say “cores”, of the Radeon HD 7990 are the same as the single GPU 7970 versions. It carries 2048 SPUs, 128 TAUs and 32 ROPs on each GPU, so in a sense you can double those figures.


Connecting the two graphics processors is the PEX bridge from PLX Technologies, which is the same method employed by all previous AMD dual-GPU graphics cards. However, the HD 7990 gets the latest 3.0 PEX8747 bridge which boasts 48 PCI Express 3.0 lanes for 96GB/s of inter-GPU bandwidth.

Cooling the "Malta" GPU are two massive aluminum vapor chamber heatsinks, each with 62 fins and four heatpipes. The vapor chamber design was first implemented by the Radeon HD 5970 and has since been adopted by numerous high-end AMD and Nvidia graphics cards. Heat is dispersed by a trio of 75x20mm axial fans that pull air in from inside the case and push it out the back.


The HD 7990’s fan operates quietly for the most part, but despite the card's impressive idle consumption of just 15 watts, it still chugs up to 375 watts under load, so the fan does kick up a little during heavy gaming sessions.

The heatsink and fan are enclosed in a custom housing that conceals the entire graphics card, a common practice for AMD flagship products and one we tend to like. Nvidia has also done this in the past, though this is a design method that is typically reserved for only the most high-end products.

To feed the card enough power, AMD includes dual 8-pin PCI Express connectors — the same setup you'll find on the HD 6990.


Naturally, the HD 7990 supports QuadFire (Crossfire) and so there is a connector for bridging with another card. The only other connectors are on the I/O panel. Our AMD reference sample has a dual DL-DVI connector and four mini-DisplayPort 1.2 sockets which allows support for five simultaneous monitors right out of the box.

Benchmarks: Battlefield 3, Crysis 3

The Radeon HD 7990 is the fastest graphics card we have tested in Battlefield 3 at 2560x1600 as it just managed to outpace the GeForce GTX 690, beating it by a 4% margin. The 7990 was also faster than the 7970 GHz Edition Crossfire configuration which was surprising. When compared to the GeForce GTX Titan the 7990 was 39% faster, while it crushed the GTX 680 by a 96% margin and the 7970 by a 101% margin.

Despite beating the GeForce GTX 690 by a 4% margin in our frames per second testing, the Radeon HD 7990 was actually 30% slower when it came to frame time performance. Frame time performance is a weakness of Crossfire technology (at least for the moment) and this is where the 7990 is going to struggle.

Although the Radeon HD 7990 was able to average 37.1fps in Crysis 3 at 2560x1600, making it 57% faster than the 7970 while also matching the 7970 GHz Edition cards, it was 10% slower than the GeForce GTX 690.

Frame time performance in Crysis 3 does not appear to be a problem for Crossfire technology, as the Radeon HD 7990 took just 31.6ms between frames at 2560x1600. That said, it was now 20% slower than the GeForce GTX 690, but 47% faster than the GTX 680.

Benchmarks: DiRT 3, Far Cry 3

The Radeon HD 7990 spat out 140fps at 2560x1600 in DiRT 3, allowing it to match the performance of the 7970 GHz Edition Crossfire cards. This then meant that the 7990 was 17% faster than the GeForce GTX 690 and 50% faster than the GTX Titan.

The DiRT 3 frame time performance of the Radeon HD 7990 wasn’t bad either and although the GeForce GTX 690 did sneak ahead there wasn’t much in it. The 7990 was just 3% slower than the GTX 690, while it was 11% faster than the GTX Titan and 4% faster than the 7970 GHz Edition Crossfire cards.

The Radeon HD 7990 average 60.3fps in Far Cry 3 at 2560x1600 to narrowly beat the GeForce GTX 690 by a 1% margin. Surprisingly this meant that the 7990 was 5% slower than the 7970 GHz Edition Crossfire cards. Still it was 27% faster than the GeForce GTX Titan, 91% faster than the GTX 680 and 73% faster than the Radeon HD 7970.

The Crossfire frame time performance is very poor in Far Cry 3 and here the Radeon HD 7990 took an average of 43.2ms between frames, which is slower than a single Radeon HD 7950 or GeForce GTX 670 graphics card. As a result the Radeon HD 7990 was 44% slower than the GTX 690, 42% slower than the GTX Titan and 20% slower than the GTX 680.


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Steven Walton is a writer at TechSpot. TechSpot is a computer technology publication serving PC enthusiasts, gamers and IT pros since 1998.