ATI Radeon HD 4870 X2: Specifications and Innovations
Conceptually, ATI’s new attempt to create the world’s fastest graphics card differs but slightly from the Radeon HD 3870 X2. It just employs new-generation RV770 cores instead of RV670 and GDDR5 memory instead of GDDR3. It has the following specifications (in comparison with its opponent and predecessor):
You can see that both dual-RV770 cards are equipped with 2 gigabytes of onboard memory, which is more than the Radeon HD 3870 X2 had. For technical reasons, applications can make use of only 1 gigabyte of this memory, as you know. So, these cards are equal to the GeForce GTX 280 in this respect or even slightly better considering the more efficient memory management of ATI’s solutions. The Radeon HD 4800 X2 cards are going to show their best in new-generation games and/or at extreme resolutions (above 1920x1200 pixels). We will check this supposition out in our tests soon. The senior model has a total memory bandwidth of over 200GBps. The junior model’s 128GBps bandwidth is lower than that of the GeForce GTX 280, but quite high anyway.
The sheer amount of the new cards’ computing resources is astounding as they have as many as 1600 ALUs. ATI claims the senior model of the new series can perform at 2.4 teraflops which is an industry record. The Radeon HD 4870 X2 are going to be only about half that fast at double-precision computations, but this is far faster than what the GeForce GTX 280 can do anyway. As concerns texture mapping and rasterization/antialiasing, the Radeon HD 4800 X2 are equal to Nvidia’s flagship solution, but the latter’s texture processors are less effective in practice and we can expect the new cards to be better from this aspect, too.
The above-mentioned innovations are interesting, yet not really innovative. The cards are just equipped with more resources than before. But there are some truly new features about the new Radeon HD 4800 X2. First, it is the interface type. The previous generation of ATI’s dual-processor cards supported PCI Express 1.1 whereas the new series is endowed with PCI Express 2.0 thanks to a second-generation PCI Express switch. The communication channel between the two GPUs is thus twice as wider as before (5GBps rather than 2.5GBps in each direction) which is important since many rendering techniques employed in modern games require data transfers between the GPUs in a multi-GPU subsystem.
The Radeon HD 4800 X2 also have something the Radeon HD 3870 X2 had not. We mean an additional data-transfer channel called Sideport. This is a direct link between the two GPUs that provide an additional bandwidth of 5GBps in each direction. Thus, the total theoretical bandwidth of the internal interfaces of the Radeon HD 4800 X2 cards is as high as 21.8GBps which eliminates any possibility of a bottleneck and improves the overall scalability of CrossFireX technology. This additional data-transfer channel can hardly be called for in modern games, though. This must be the reason why the Sideport interface is currently disabled on the software level.
At the moment of its announcement the new graphics card series includes two models of Radeon HD 4800 X2 differing in clock rates and memory type. They come at a recommended price of $549 for the senior model and $399 for the junior model. We’ve got a sample of the senior version of the card equipped with GDDR5 memory. It is the more interesting of the two because the Radeon HD 4870 X2 is the solution that must beat Nvidia’s GeForce GTX 280. ATI’s fans pin their hopes on it. Our sample is manufactured by Tul Corporation, the supplier of graphics cards under the PowerColor brand. Let’s check out the packaging and accessories of this product first.