The ATI Radeon HD 3870 X2
At first glance, the Radeon HD 3870 X2 looks much like AMD’s previous high-end GPU offerings. The card features ATI’s signature red PCB with an up-close-and-personal look into Ruby’s eyes emblazoned on the fan shroud. Flip the card over, however, and it becomes abundantly clear that the Radeon HD 3870 X2 has a lot going on under its cooler.
As we’ve already mentioned, the Radeon HD 3870 X2 is powered by a pair of RV670 GPUs, the same chips used on the Radeon HD 3870 and 3850. The two GPUs are linked together on the PCB through a PCI Express fan-out switch from PLX. That switch takes the 16 PCI express lanes coming from the PEG slot and distributes them to both of the GPUs. We should note, however, that although the RV670 GPU has a native PCI Express 2.0 interface, the on-board switch is PCI Express 1.1 compliant only. Also note that the 3870 X2 has only a single CrossFire edge connector along the top of its PCB. It has only one because the other connection is already utilized on the PCB. Although the Radeon HD 3870 X2 is equipped with a CrossFire connector, at this time drivers are not available that will allow end users to link two of these cards together for quad-GPU CrossFireX. Those drivers are coming though.
Each of the GPUs on the Radeon HD 3870 X2 has its own 512MB frame buffer, for a total of 1GB of on-board memory. As you can see, the entire assembly is quite large and results in a 10.5” PCB – a little longer than a standard ATX motherboard. The cooler used on the card is much like previous offerings, but there are some noteworthy elements to the design. Each of the GPUs gets its own all copper heatsink, but the surrounding heatplate and heatsinks for the switch and RAM is made of aluminum. AMD went with a hybrid aluminum and copper cooler to keep the card’s weight down, but it is still quite heavy.
Like the other members of the Radeon HD 3800 series, AMD’s reference ATI Radeon HD 3870 X2 has a pair of dual-link DVI outputs, and an HD video output. One of the DVI outputs can be converted to an HDMI output with audio using an included adapter. Because the Radeon HD 3870 X2 has dual GPUs though, it is capable of supporting four DVI outputs.
If you look at the breakdown above, the Radeon HD 3870 X2 isn’t simply two Radeon HD 3870s fused together on a single PCB. The GPUs on the Radeon HD 3870 X2 will be clocked at a minimum of 825MHz, up from the standard 3870’s 775MHz. The X2’s frame buffer memory will be clocked lower, however, 1.8GHz vs. 2.25GHz. What this means is that in applications that are limited by shader performance and fillrate, the X2 should be faster than a pair of Radeon HD 3870 cards running in CrossFire mode. Conversely, in applications that are memory bandwidth bound, the dual-card CrossFire configuration should be somewhat faster.