NVIDIA GeForce 7950 GX2
The 7950 GX2 isn't exactly a secret, given NVIDIA's wheezing, asthmatic attempt to bring the whole Quad SLI concept to market. The technology uses engineered GeForce boards that layer a pair of PCBs, each with its own GPU and memory system for a single-board SLI setup, which, when paired with another, gets you your Quad.The first iteration of those boards were big and beefy and available via system integrators only. And it turns out that it's not quite ready for the primetime, other publications reporting on instability, game incompatibility and integration issues (among a myriad of complaints) with the first systems that made their way out for review. We wonder how many Quad SLI systems Dell -- initiators of the technology with NVIDIA -- have sold to date.
The GeForce 7950 GX2 is that same half of a Quad SLI setup, but for the time being it's being sold and supported in single board configuration mode only, with its own 'regular' two-GPU SLI implementation -- a config that's been maturing since its inception in November '04.
That there's a pair of G71 GPUs on each GX2 means the board has some interesting on-paper performance properties, when combined with SLI. Rather than make the tedious tabular comparison between 7950 GX2, 7900 GTX and Radeon X1900 XTX that you'll undoubtedly see elsewhere, we'll simply say that it's SLI of a full G71 configuration with 500/600 clocks (VS clock domain the same as the PS one) and 512MiB attached.
That's really all you need to know, and understanding of those clocks and that memory configuration will have you placing it somewhere between 7900 GT (450/660, with 470 VS clock and only 256MiB) and 7900 GTX (650/800, with 700 VS clock and 512MiB) in SLI, on paper at least.
Where does the SLI differ?
Good question, glad you asked.Where the GX2's SLI implementation claims to deviate from the norm is in its support for non-NVIDIA platforms. It's supposed to work on anything with a PCI Express x16 slot (PEG16X), with NVIDIA currently providing updated lists of mainboards its tested it on, from Intel's i955X and i975X reference boards, to ATI Radeon Xpress 3200 boards that take AMD processors. Yes, it purports to work in SLI mode on 'Crossfire' mainboards. It's the driver in the main that regulates the restriction, but there is board-level support for it to work correctly, too.
The GX2 uses PCI Express switching hardware that's a discrete physical hardware device as far as the system is concerned, and which appears to the operating system as a device requiring driver support. Depending on the PCI Express host controller that that GX2 is connected to via the bus, it might not be 'visible' on the far side of the controller and therefore be configurable and supported by that mainboard platform.
More on that and the compatibility later.
So it's single-board SLI that apparently works anywhere it fits (with some caveats), with a clock and memory config that places it (for just a single layer of the board) in between NVIDIA's two other main G71-sporting SKUs. SLI is therefore where it gets its performance and IQ advantages via those other single board products, in theory.
We know how the 7950 GX2's main competitors stack up to each other, so let's look at the board itself, shall we?
