Through a SidePort connection on each of these graphics processors, there is 5GB/s link in each direction between the GPUs. Additionally, through the PCI Express 2.0 bridge is another 5GB/s link each way. The SidePort capability is a new feature that wasn't previously found on the Radeon HD 3870 X2. The VisionTek X2 graphics card has 2GB of GDDR5 memory, which allows 1GB for each GPU.
The Radeon HD 4870 X2 has two dual-link DVI connectors with the third output being for the HDTV Component video. The HD 4870 X2 has an integrated 7.1 channel HDMI audio processor, if using the included HDMI adapter. This sound capability is supported on Linux through ALSA.
Up to four GPUs are supported with ATI CrossFire X meaning that two of these Radeon HD 4870 X2 graphics cards can be linked together. However, the Catalyst Linux driver at this time only supports CrossFire between two GPUs. You can still use two Radeon HD 4870 X2 graphics cards in a Linux system for supporting multiple monitors but CrossFire will not function.