What is Scalable Link Interface and Crossfire

[Cup_o_Joe]

If anyone wanted to know the difference here’s your answer:

@Wikipedia article on Scalable Link Interface

The basic idea of SLI is to allow two or more graphics processing units (GPUs) to share the work load when rendering a 3D scene. Ideally, two identical graphics cards are installed in a motherboard that contains two PCI-Express x16 slots, set up in a master-slave configuration. Both cards are given the same part of the 3D scene to render, but effectively half of the work load is sent to the slave card through a connector called the SLI Bridge. As an example, the master card works on the top half of the scene while the slave card works on the bottom half. When the slave card is done, it sends its output to the master card, which combines the two images to form one and then outputs the final render to the monitor.

@Wikipedia article on Crossfire

Second-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.[4] 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.

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.[5] 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.[6] 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 to the CrossFire infrastructure include a dual GPU solution with on-board PCI-E bridge that was released in early 2008, the Radeon HD 3870 X2 and later in Radeon HD 4870 X2 graphics cards, featuring only one CrossFire connector for dual card, four GPU scalability.

Circuit using Master card ideology:

Lets say we use “master card” method. Lets say the resistance is a video card, As you can see, the circuit starts in series which means that the last three work for the first one as “slaves” meaning if the first card doesn’t work, the rest won’t either because the current (API) for the last three (in parallel) came from the first resistance (video card) which was part of a series circuit.

Parallel circuit without using Master card ideology:

In a parallel circuit, the resistances (in this case video cards) are working together on the same circuit (in this case the PCIE bus and the API like Crossfire) but are entirely independent also. The circuit continues regardless of if it is enabled or not.

Pretty much SLI, the first card is master regardless if you want everything to work independently. Crossfire on the other hand all the cards work interdependent of each other which is better for multiscreen setups.

[Level]

Interesting thread, I’ll read it when I have more time to go over it throughly.

Which is better?

[Cup_o_Joe]

the API, Crossfire because it is completely parallel, not one is in charge but all of them work together unlike SLI which the 2nd 3rd and 4th would be working for the first for better rendering of the 2 or 4 displays. It’s sort of like Christmas lights. In parallel you can see which light isn’t on. In series, if one light goes out, the entire circuit stops which is how SLI API starts with the first card aka master.

Crossfire is compatible with any card from that generation of crossfire capable video cards. Because it’s in Parallel, each card can be used to display while all of the cards work together on each screen like in the Wikipedia SLI description which means crossfire can have up to 8 screens with the scaling, while SLI can only have up to 4 with all 4 cards enabled in the APIs. But if SLI is disabled and all of the cards are enabled, you can use all of the screens but without scaling.

[iKy]

crossfire is much more flexible , for long-term investments , nvidia is more like , buy 2-3 of the best video cards yet and hope it lasts…

[Cup_o_Joe]

Yeah, pretty much Crossfire can scale and display at the same time on each newer ATI video card when Crossfire is enabled.