For some years now, AMD has stopped short of bringing out a true high-range graphics chip, choosing instead to take its best chip and place two of them on the same card. Given that the 7990 follows in this line – essentially bolting two 7970 Tahiti chips onto the one card – it's perhaps surprising that we haven't seen this launch long before now. After all, we reviewed the 7970 well over a year ago now. The main surprise though is that this is no mere half-baked attempt at doubling resources. See Group test: what's the best graphics card?
Previous dual-GPU cards have tended to throttle back on the specifications. Essentially, you get two GPUs in one, but you get them clocked to slightly slower speeds and cut down in processing features here and there. But the 7990 not only doesn't drop the specifications – it actively increases them. See also: Nvidia GeForce GTX 670 review.
The core clock of 950MHz is 25MHz higher than that of a 7970, for example. In addition, the AMD Radeon HD 7990 comes with a boost clock, so it can push the total speed up to 1GHz. The memory clock of 1500MHz (6GHz DDR effective) is substantially faster than the 1375MHz (5.5GHz DDR) of the 7970. See all PC Components and Upgrades reviews.
These figures are very competitive with nVidia’s GeForce GTX Titan too, the latter coming with an effectively equivalent memory clock of 1502MHz (6008MHz DDR effective), but a vastly inferior core clock of 876MHz.
The dual-GPU GTX 690 matches the Titan's memory clock, but generally trails the 7990 on core-clock speed by around 35MHz.
In addition to the 7990's impressive clock speeds, many of the other specifications are doubled by having two GPUs. So you get two lots of 2048 stream processors, as well as double the 128 texture units and 32 raster operations of the 7970.
In all cases, these eclipse the Titan's figures of 2688 stream processors, and 224 texture units and 48 raster operations.
The GTX 690 matches the 7990 on texture units and raster operations, but falls behind on stream processors, packing two lots of 1536.
The AMD Radeon HD 7990, 7970 and Titan all have 384-bit memory interfaces. The 7990, though, has two of them. This essentially gives the 7990 a memory bandwidth of 2 x 288 GB/s, in comparison with the 288.4 GB/s of the Titan, and the 264 GB/s of the straight 7970.
It fares very well on texture-fill rates too, coming up with a maximum of 2 x 128 GT/s, as opposed to 196.2 GT/s on the Titan, and 118.4 GT/s on the 7970. It's a little hard to say exactly how these figures play out in the real world, as dual GPUs don't really offer double the actual performance of their single GPU counterparts. Nonetheless, the 7990 has some fantastic figures on paper, even stretching to its two helps of 3GB of memory.
Given that it's a dual-GPU card, you wouldn't expect the 7990 to be low on power consumption. But seeing that a single 7970 has a TDP of 250 watt, and that the 7990 doesn't hold back on its clock speeds, it's very impressive that this card has a given TDP of just 375 watt. So the extra GPU effectively only draws half as much power again.
Of course, this in no way compares to the nVidia Titan's ‘mere’ 250 watt TDP; or even to the GTX 690's 300-watt figure.
In testing we were hitting figures of just over 303-306 watt on the 7990 itself, while a Titan was down in the region of 214-218 watt. The GTX 690 sat somewhere between the two, on around 261-263 watt.
Sound levels are good too. The 7990 isn't quite as quiet as the Titan, but the AMD's rather immense (and not unattractive) three-fan design is only marginally louder, adding a couple of decibels to the room levels in our tests.
The card demands two eight-pin power connectors, so be sure that you have suitable connectors on your motherboard.
AMD Radeon HD 7990: Performance
The 7990 takes the single-card performance crown from the dual-GPU nVidia GTX 690. But only just.
In practice, we're talking about two or three frames here and there. That makes it a few frames faster again than the GeForce Titan. In Crysis 2, the 7990 hit 78.3 and 55.0fps at resolutions of 1920 x 1200 and 2560 x 1600, as opposed to the 690's figures of 75.8 and 53.1fps.
The Titan is quite close at 1920 x 1200, but falls far behind at our top 2560 x 1600 resolution setting, with 45.3fps.
In Stalker: Call of Pripyat, the 7990 manages 139.9 and 103.8fps, again narrowly beating the 690's 137.3 and 101.6fps.
The nVidia Titan is even further behind here, trailing on 121.7 and 91.0fps. Battleforge sees another tight victory for the AMD 7990, posting figures of 114.8 and 83.7fps, against the nVidia GTX 690's 113.2fps and 82.3fps.