AMD CrossFire (also known as CrossFireX) is a brand name for the multi-GPU technology by Advanced Micro Devices, originally developed by ATI Technologies. The technology allows up to four GPUs to be used in a single computer to improve graphics performance.
The CrossFire brand name was retired by AMD in September 2017, however the company continues to develop and support the technology for DirectX 11 applications. For DirectX 12 applications, AMD has the mGPU (also known as multi-GPU) branding, with the difference being that software developers must create mGPU compatible profiles for their applications where before AMD created the profiles for DirectX 11 applications.
CrossFire was first made available to the public on September 27, 2005. The system required a CrossFire-compliant motherboard with a pair of ATI RadeonPCI Express (PCIe) graphics cards. Radeon x800s, x850s, x1800s and x1900s came in a regular edition, and a “CrossFire Edition” which has “master” capability built into the hardware. “Master” capability is a term used for 5 extra image compositing chips, which combine the output of both cards. One had to buy a Master card, and pair it with a regular card from the same series. The Master card shipped with a proprietary DVI Y-dongle, which plugged into the primary DVI ports on both cards, and into the monitor cable. This dongle serves as the main link between both cards, sending incomplete images between them, and complete images to the monitor. Low-end Radeon x1300 and x1600 cards have no “CrossFire Edition” but are enabled via software, with communication forwarded via the standard PCI Express slots on the motherboard. ATI currently has not created the infrastructure to allow FireGL cards to be set up in a CrossFire configuration. The “slave” graphics card needed to be from the same family as the “master”.
An example of a limitation in regard to a Master-card configuration would be the first-generation CrossFire implementation in the Radeon X850 XT Master Card. Because it used a compositing chip from Silicon Image (SiI 163B TMDS), the maximum resolution on an X850 CrossFire setup was limited to 1600×1200 at 60 Hz, or 1920×1440 at 52 Hz. This was considered a problem for CRT owners wishing to use CrossFire to play games at high resolutions, or owners of Widescreen LCD monitors. As many people found a 60 Hz refresh rate with a CRT to strain one’s eyes, the practical resolution limit became 1280×1024, which did not push CrossFire enough to justify the cost. The next generation of CrossFire, as employed by the X1800 Master cards, used two sets of compositing chips and a custom double density dual-link DVI Y-dongle to double the bandwidth between cards, raising the maximum resolution and refresh rate to far higher levels.