ATI CrossFire

ATI CrossFire

CrossFire (also CrossFire X after release of the "Spider" desktop platform on November 19, 2007) is a brand name for ATI Technologies' multi-GPU solution, which competes with Scalable Link Interface (SLI) from NVIDIA. The technology allows up to four graphics cards to be used in a single computer to improve graphics performance. Although only recently announced for consumer level hardware, similar technology known as AMR has been used for some time in professional grade cards for flight simulators and similar applications available from Evans & Sutherland, ATI had also previously released a similar dual RAGE 128 consumer card called the Fury MAXX.



CrossFire was first made available to the public on September 27, 2005. [cite web|url=|title=Slashdot]

The system required a CrossFire-compliant motherboard with a pair of ATI Radeon PCI 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. [ [ Tech Report] article on CrossFire] One had to buy a Master card, and pair it with a regular card from the same series. The Master card would have shipped with a proprietary DVI Y-dongle, which would plug into the primary DVI ports from 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 ones eyes, the practical resolution limit became 1280×1024, which did not push CrossFire enough to justify the cost. [ [ HardOCP] article on CrossFire] 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.

econd-generation (Software CrossFire)

When used with ATI's "CrossFire Xpress 3200" motherboard chipset, the 'master' card is no longer required for every "CrossFire Ready" card (with the exception of the Radeon X1900 series). With the CrossFire Xpress 3200, two normal cards can be run in a Crossfire setup, using the PCI-E bus for communications. This is similar to X1300 CrossFire, which also uses PCI Express, except that the Xpress 3200 had been built for low-latency and high-speed communication between graphics cards. [ [ Anandtech] article on the Xpress 3200] While performance was impacted, this move was viewed as an overall improvement in market strategy, due to the fact that Crossfire Master cards were expensive, in very high demand, and largely unavailable at the retail level.

Although the CrossFire Xpress 3200 chipset is indeed capable of CrossFire through the PCI-e bus for every Radeon series below the X1900s, the driver accommodations for this CrossFire method has not yet materialized for the X1800 series. ATI has said that future revisions of the Catalyst driver suite will contain what is required for X1800 dongleless CrossFire, but has not yet mentioned a specific date.

Current generation (CrossFire X)

With the release of the Radeon X1950 Pro (RV570 GPU), ATI has completely revised CrossFire's connection infrastructure to further eliminate the need for past Y-dongle/Master card and slave card configurations for CrossFire to operate. ATI's CrossFire connector is now a ribbon-like connector attached to the top of each graphics adapter, similar to nVidia's SLi bridges, but different in physical and logical natures.cite web|url=|title=AnandTech] As such, Master Cards no longer exist, and are not required for maximum performance. Two dongles can be used per card; these were put to full use with the release of CrossFire X. Radeon HD 2900 and HD 3000 series cards use the same ribbon connectors, but the HD 3800 series of cards only require one ribbon connector, to facilitate CrossFire X. [ [ bit-tech review of the HD 3870] , retrieved January 25, 2008] Unlike older series of Radeon cards, different HD 3800 series cards can be combined in CrossFire, each with separate clock control.

Since the release of the codenamed "Spider" desktop platform from AMD on November 19, 2007, the CrossFire setup has been updated with support for a maximum of four video cards with the 790FX chipset; the CrossFire branding was then changed to "ATI CrossFire X". The setup, according to internal testing by AMD, will bring at least 3.2x performance increase in several games and applications which required massive graphics capabilities of the computer system, the setup is targeted to the enthusiast market. A later development include a dual GPU solution that was released in early 2008, the "ATI Radeon HD 3870 X2", featuring only one CrossFire connector for dual card, four GPU scalability.

Comparisons to NVIDIA SLI


* ATI has opened the Crossfire architecture to Intel, allowing CrossFire to be enabled on certain Intel chipsets which boast two 16x PCI-E slots. SLI, however, requires a motherboard which is SLI certified (usually based on nForce chipset, such as the nForce 590 SLI, nForce 680i SLI, and nForce 790i which are often prone to problems and Nvidia is slow to offer fixes and sometimes opts to design a new chipset rather than try and fix the existing one).
* On the codenamed "Spider" platform, utilizing CrossFireX with AMD 790FX chipset and Radeon HD 3800 series video cards, the user can use multiple displays and maintain CrossFire functionality while SLI and previous generation CrossFire setups are limited to one display only.cite web|url=|title=TechReport]


* If an OpenGL game does not have a Crossfire profile, the Catalyst AI system will set the rendering mode to Scissor by default, with no way to change it to a more suitable or faster mode, such as AFR. However SLI allows the rendering mode to be set for each application manually, even for games which do not have an existing profile. It should be noted that setting Catalyst AI to 'Advanced' allows manual mode setting for Direct 3D games, but not OpenGL games, to AFR.
* The first generation CrossFire implementations (the Radeon X800 to X1900 series) require an external y-cable/dongle to operate in CrossFire mode due to the PCI-e bus not being able to provide enough bandwidth to run CrossFire without losing a significant amount of performance.

ee also

* Scalable Link Interface
* Comparison of ATI chipsets
* Comparison of AMD chipsets


External links

* [ ATI's CrossFire official site]
* [ ATI CrossFireX Technology Information Site]
* ['s CrossFire preview]
* [ Slashdot coverage on the release of the system]
* [ SLI vs. CrossFire]

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