The Card
In many ways the design of the Radeon HD 4870 X2 resembles that of the original 3870 X2. Compared to the single-GPU Radeon HD 4870, the X2 is a few centimeters longer, measuring at 27cm. (10.6 in).
Although this sounds a bit excessive, this happens to be the same length of the high-end Nvidia GeForce GTX 280 graphics card that uses a single GPU.
The stock cooler on the Diamond Radeon HD 4870 X2 is very large (should be the same in other cards following AMD's reference design), and given that it includes two large copper base plates, it is also very heavy.
A single 80mm blower fan is used to draw air from within the case, pushing it over the heatsinks fins where it will quickly warm up and then exit the case through the rear of the case. This is exactly the same design used in all high-end graphics cards from AMD and Nvidia for some time now.
Flipping the 4870 X2 over exposes something a little unusual for a reference Radeon graphics card, the PCB is black. Rather than going with ATI's traditional red, it seems that AMD has decided that the world's fastest graphics card deserves a more sinister-looking paint job.
There is also a black heat spreader on the rear of this graphics card, much like there was on the Radeon HD 3870 X2. This heat spreader is used to cool down the memory chips placed on the rear of the graphics card.
Removing the heatsink exposes the two GPUs, GDDR5 memory chips, and a few other critical components. In fact, with the heatsink off the Radeon HD 4870 X2 looks almost identical to the Radeon HD 3870 X2 we reviewed back in February.
The key changes involve the new GDDR5 memory, improved power circuitry, and an updated PEX bridge from PLX Technologies, which is used to link the GPUs together. All this hardware is cooled via the large heatsink that covers the majority of the 27cm long PCB.
Also worth mentioning is that the Radeon HD 4870 X2 features two additional power connectors, a 6-pin and an 8-pin connector. This is the same configuration used by the GeForce 9800 GX2, for example, so current high-end power supplies should cater for this new graphics card.
The Radeon HD 4870 GPU, of which the Radeon HD 4870 X2 carries two, uses a 55nm design just as the Radeon HD 3000 series did. This has allowed ATI to be quite aggressive with the core speed, clocking it at 750MHz.
The GDDR5 memory works at an ever more impressive frequency (1.8GHz x 2) on this particular model, while the card features a total memory capacity of 2GB. The core configuration of the Radeon HD 4870 GPU includes 800 SPUs, 40 TAUs (Texture Address Units), and 16 ROPs (Rasterization Operator Units).
Diamond is shipping their Radeon HD 4870 X2 with Hynix ICs on-board (H5GQ1H24MJR-T0C parts). These GDDR5 modules are rated for 2.0GHz operation, so we expect to be able to push them much further than stock 1.8GHz.
This is something we will investigate come time to overclock. Each GPU features its own 256-bit wide memory bus, though we are sure that board partners will not hesitate to whack a 512-bit memory bus sticker on the box.