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Test: AMD Radeon HD 7990

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Andreas Schilling

Page 1: Test: AMD Radeon HD 7990

amd-radeon-logo-2013Announced as "New Zealand" in December 2011, the Radeon HD 7990 will now be released with several months delay under the codename 'Malta'. In essence, however, it is the same card that was already planned 16 months ago. But why does AMD release the first Radeon HD 7990 for potential buyers only today? We have no answer to this, though we will definately answer the probably more urging question about its performance. But before we get into the benchmarks, let's have a closer look at the Radeon HD 7990 in its reference version.

AMD has been dallying for months with the idea to release a Radeon HD 7990, but probably had several reasons to be dissuaded from it again and again. The most important ones are likely to be technical difficulties. A few AMD partners already talked to us at the Computex 2012 regarding these issues. Most likely, AMD had trouble with PLX's PCI Express switch PEX8747. However, we couldn't really make out any problems of this kind on the NVIDIA GeForce GTX 690, nor on both the ASUS ARES II (Hardwareluxx Review) and the PowerColor HD7990 Devil 13 (Hardwareluxx Review). Only the issue of micro stuttering, very much recurrent in multi-GPU systems, seems to have been handled better by NVIDIA than by AMD.

Before we go ahead presenting the 7990 AMD Radeon HD in detail, and sending it through our usual comprehensive benchmarking suite, we will take a closer look at the architecture of the GPU and approach that AMD has in mind with this card.

AMD Radeon HD 7990 Press Information

Dual-GPU cards are not a novelty for AMD, and with almost every new GPU generation, they were able to release a model meant to go for the pole position in performance. But since NVIDIA is pursuing the same plans, the winner in this race is not always clear-cut. With the Radeon HD 7990, AMD surely took a lot of time, since NVIDIA had already introduced their dual-GPU card based on their current architecture (the GeForce GTX 690) almost a year ago.

AMD Radeon HD 7990 Press Information

However, with the Radeon HD 7990, AMD is not entering an entirely new development area for desktop pcs, but instead uses the FirePro S10000's technology in a desktop variant, with adjusted clock speeds. This is of course common practice, though in some cases, adjustments to at least the cooling solution are necessary.

AMD Radeon HD 7990 Press Information

Two times 4.3 billion transistors will be operating in the Radeon HD 7990, thus superseding the GeForce GTX 690 with its 2x 3.52 billion transistors and the GeForce GTX Titan with its 7.1 billion transistors. The Radeon HD 7990 achieves 8.2 TFLOPS in single-precision. For comparison, the GeForce GTX Titan achieves 4.5 TFLOPs, and the GeForce GTX 690 nearly hits the 6 TFLOPS-mark.

AMD Radeon HD 7990 Press Information

Each GPU has 3 GB of GDDR5 memory at its disposal, meaning that that the Radeon HD 7990 has a total of 6GB. But this cannot be directly compared with the 6 GB of the GeForce GTX Titan, since the GPU used has access to the full 6 GB. In essence, the memory usage of the Radeon HD 7990 can be compared to the Radeon HD 7970's 3GB. The simple addition of the amount of memory does not really play an important part in this matter.

AMD Radeon HD 7990 Press Information

A "Tahiti" GPU is able to control up to six displays, theoretically enabling a Radeon HD 7990 to access even significantly more displays than the advertised five. Since half of the slot panel should remain free for further use, and since AMD has decided to implement an additional dual-link DVI output, this should be more than enough for the rare Eyefinity systems with up to five displays should.

AMD Radeon HD 7990 Press Information

During the preliminary stages of publication, rumors abounded that AMD could have developed their own chip for communication between the GPU and the common PCI Express interface. Ultimately, however, AMD implemented the PLX PEX8747, well-known from numerous other dual-GPU cards.

AMD Radeon HD 7990 Press Information

The more heat is generated, the more it must be dissipated from GPUs, and from memory chips and other components. A dual-GPU card is therefore always a challenge for the design of the cooler. For the Radeon HD 7990, AMD uses the same cooler as in the professional FirePro S10000 variant. Three fans and a massive heatsink are to provide a silent cooling system for the card. We will see in the measurements section whether this was successfully implemented.

AMD Radeon HD 7990 Press Information

Zero Core Power is a technology that was introduced with the Radeon HD 7000 series, and ensures that idle power consumption is as low as possible. Nowadays, graphics cards consume only 10-15 watts when idling, with active 2D output to the display. When the display is turned off, Zero Core Power shuts off further parts of the GPU, consequently also shutting down the fan. In 2D mode, the Radeon HD 7990 is also able to disable one of the two GPUs, thus saving even more power, not to mention sparing the nerves of the user thanks to lower fan noise.

Architectural Facts

Now that we have reviewed the most important features of the Radeon HD 7990, we will focus on the technical data.

AMD Radeon HD 7990
Street Price approx. 900 euros
Homepage www.amd.com
Technical Data
GPU 2x Tahiti XT
Manufacturing Process 28 nm
Transistors 2x 4,3 Billion
GPU Clock (Base Clock) 1000 MHz
GPU Clock (Boost Clock) 1000 MHz
RAM Clock 1500 MHz
RAM Size 2x 3072 MB
RAM Interface 2x 384 Bit
RAM Bandwidth 2x 288 GB/s
DirectX Version 11.1 
Shader Units 2x 2048 (1D)
Texture Units 2x 128
ROPs 2x 32
Pixel Filling rate 2x 32 GPixel/s
SLI/CrossFire CrossFire

The Radeon HD 7990 features two Radeon HD 7970 "Tahiti XT" GPUs. However, obviously they are not "XT2 Tahiti" GPUs, such as implemented on the ASUS ARES II (Hardwareluxx Review) and the PowerColor HD7990 Devil 13 (Hardwareluxx Review). The two GPUs are being operated at a fixed clock speed of 1000 MHz. AMD seems to forego a clock speed increase using PowerTune. The 3072 MB of GDDR5 memory per GPU each operate at 1500 MHz, and are connected with a 384-bit memory interface. The memory bandwidth amounts to 288 GB/s, which identical to the Radeon HD 7970 GHz Edition bandwidth.

The use of two "Tahiti XT" GPU makes for a total of 4096 stream processors, 256 texture units and 64 ROPs. On the following page we will compare the architectural data with both the GeForce GTX 690 and GeForce GTX Titan. This way, at least on paper, it's easy to determine how well AMD is going to be positioned with the Radeon HD 7990 in the market.