Design and Functionality
By today, nearly all of AMD partners have released reference-design Radeon HD 7990s in eye-catching packaging and with interesting accessories (including games of the Never Settle Reloaded bundle). Ours is an OEM version, though. It was manufactured in China.
The AMD Radeon HD 7990 is a rather long graphics card. Its length is 310 mm as opposed to the GeForce GTX 690’s 280 mm and the GeForce GTX Titan’s 267 mm. But, in our opinion, the AMD card is more beautiful. Its face side is covered with a glossy black casing with three red fans:
On the reverse side, we can see back-plates opposite the GPU heatsinks. The rest of the PCB is covered with a metal plate, which serves as a heat-spreader. There are slits in the cooler casing for some air flow. The hot air is exhausted through the card’s mounting bracket.
There are five video connectors here: one dual-link DVI and four mini-DisplayPorts version 1.2.
The AMD Radeon HD 7990 features one connector for building CrossFireX configurations. You can see a small BIOS switch next to it:
At the other end of the PCB there are two 8-pin power connectors. The Radeon HD 7990 is specified to consume 375 watts in 3D applications, which is 25% and 50% higher than specified for the GeForce GTX 690 and GeForce GTX Titan, respectively. Its 2D power draw is up to 95 watts. Like ordinary Radeon HD 7970s, it only needs 3 watts of power in sleep mode.
The sophisticated PCB is populated with two GPUs, 24 memory chips, a PCIe switch chip, and a lot of power components.
The high component density might be expected since one Tahiti XT needs over 150 watts of power, so it takes some serious engineering effort to make two such chips live happily on one PCB.
The 4-phase power system of each GPU is managed by a Volterra VT1556MF controller.
Each power system also includes two phases for graphics memory and one phase for PLL. The MOSFETs below the CL1108-4-50TR-R inductor from Cooper Electronic are cooled with a separate copper heatsink with thermal pad.
A PLX PEX8747 chip is used as a PCIe switch that helps the two GPUs communicate with each other.
It supports 48 PCIe 3.0 lanes. According to the specifications, its typical power consumption is 7.3 watts. The PLX PEX8747 is not the most advanced switch offered by PLX Technology. For example, the PEX 8796 supports 96 PCIe lanes but that would be redundant for the Radeon HD 7990.
The two 28nm Tahiti XT GPUs have a die size of 365 sq. mm and incorporate about 4313 million transistors each.
The GPUs have a standard Radeon HD 7970 configuration: 2048 shader processors, 128 texture-mapping units, and 32 raster operators. They have a clock rate of 950/1000 MHz in 3D applications but it was always boosted to 1000 MHz during our tests. We can remind you that AMD’s top-end single-processor card Radeon HD 7970 GHz Edition works at 1000/1050 MHz. The clock rate of each GPU is dropped to 300 MHz in 2D mode while their voltage is lowered from 1.2 to 0.85 volts. Thanks to the ZeroCore technology, the second GPU and its accompaniments are all turned off in 2D applications.
There are 3 gigabytes of GDDR5 memory for each GPU. Populating both sides of the PCB, the H5GQ2H24AFR R0C chips are manufactured by Hynix Semiconductor.
The memory chips are rated for 6000 MHz and the card indeed uses that clock rate in 3D mode. In 2D applications the memory frequency is lowered to 600 MHz. The memory bus is 384 bits wide. We can remind you that the card has two memory sets, each exclusive to each GPU.
So, the AMD Radeon HD 7990 has the following specifications: