Double Trouble

An AMD-produced giant

AMD's graphics department has had a lot in common with the British weather this year. A lack of new hardware announcements has left enthusiasts cold and the release of a mid-range card, Radeon HD 7790, hasn't done much to dispel the growing sense of unease at the lack of brand-new architectures.

In concert with the weather warming up nicely the last week or so, AMD is also heating up its Radeon line-up with the release of a super-high-end card called the Radeon HD 7990 6GB. Hold on a second, you might say, as offshoots from the TUL Corporation already have such cards in stores, while ASUS goes further with the ARES II dual-GPU offering.

Does AMD even need such a dual-GPU card, costing around £850, in such impecunious times? Well, yes, because NVIDIA stands tall with in-house-designed GeForce GTX 690 and TITAN cards. Why let the green team take the majority of the limelight in a niche but important sector?

A familiar recipe

Following a conventional strategy of teaming two top-tier GPUs onto one board, linking them together with a PCIe bridge, and running the whole shebang in multi-GPU mode, the office-famous Table of Doom is brought out of semi-retirement.

GPU Radeon HD 7990 (6,144MB) Radeon HD 7970 GHz (3,072MB) GeForce GTX 690 (4,096MB) GeForce GTX TITAN (6,144MB) GeForce GTX 680 (2,048MB) DX API 11.1 11.1 11.1 11.1 11.1 Process 28nm 28nm 28nm 28nm 28nm Transistors 4.3bn x 2 4.3bn 3.54bn x2 7.1bn 3.54bn Approx Die Size 352mm² x2 352mm² 294mm² x2 551mm² 294mm² Processors 2,048 x2 2,048 1,536 x2 2,688 1,536 Texture Units 128 128 128 x2 224 128 ROP Units 32 x2 32 32 x2 48 32 GPU Clock/Boost (MHz) 950 (1,000) 1,000 (1,050) 915 (1,019) 837 (876) 1,006 (1,058) Shader Clock/Boost (MHz) 950 (1,000) 1,000 (1,050) 915 (1,019) 836 (876) 1,006 (1,058) GFLOPS 7,782 (8,192) 4,096 (4,300) 5,621 4,494 3,090 Memory Clock (MHz) 6,000 6,000 6,008 6,008 6,008 Memory Bus (bits) 384 x2 384 256 x2 384 256 Max bandwidth (GB/s) 288 x2 288 192.2 x2 288.4 192.2 Power Connectors 8+8 8+6 8+8 8+6 6+6 TDP (watts) 375 250 300 250 195 GFLOPS per watt 20.75 16.38 18.74 17.98 15.84 Current price $999 $449 $999 $999 $449

Analysis

Look down the two left-hand columns and the architecture is patently the same as the fastest single-GPU Radeon's, the 7970 GHz Edition. Thermals and power consumption are the two great obstacles in replicating the frequencies of the GHz Edition in a card that houses two GPUs. AMD gets pretty close, however, with the HD 7990 running at stock 950MHz core and boosting to 1,000MHz when conditions allow - this is just 50MHz slower than the GHz. Memory speed remains identical, at an effective 6,000MHz, and the board has 3GB of non-shareable RAM allocated to each GPU.

AMD's own card compares favourably with those built by partners; its frequencies are faster than the Club3D version and a tad quicker than the PowerColor variant. Only the monstrous-looking ASUS ARES II has better specifications, we note.

Perhaps the best way to understand this card is to consider it better than two HD 7970s in CrossFire but just not quite as fast as two HD 7970 GHz Editions in the same setup. HD 7990's on-paper muscle shows it has clear superiority over the GeForce GTX 690 in all performance-related areas, and priced at the same ludicrous $999 as the two NVIDIA juggernauts, it's a card for those who scoff at the economic implications of a triple-dip recession.