Nvidia's new GeForce GTX 1080 video cards will only support two-way SLI, the company has told PC Perspective, backtracking from claims made when the card was first launched.

Initially, Nvidia's plans for creating SLI setups with its latest and greatest GeForce GTX 1080 video cards were a little peculiar. Two-way configurations were supported using a new high-speed bridge to join the two cards together. Three- and four-way configurations were promised, too, but with a twist: first, these would need to use older, slower SLI bridges, and, second, system owners would have to generate a special "enthusiast key" to unlock access to three- and four-way SLI. Without this key, the system would stick to two-way.

The plan is now simpler but, for those rich individuals hoping to build the very fastest systems imaginable, somewhat worse. Configurations with two cards working in SLI using the new bridges will continue to be supported, but the company no longer plans to extend this to three- and four-way configurations at all, and the "enthusiast key" system is being dumped.

Applications that explicitly support multiple individual GPUs—either through using DirectX 12's explicit multi-adapter capability or through using APIs such as OpenCL and CUDA for GPU-based computations—will still be able to take advantage of three or four graphics cards. But applications that rely on the display driver to handle multi-GPU configurations, which is the case for traditional SLI, will only scale up to two cards. Any additional GPUs will go unused, with one small exception: Nvidia says that a future version of its drivers will enable three- and four-way configurations in certain benchmark applications, including 3DMark. All other SLI profiles will be restricted to two GPUs.

The focus on two-way SLI makes a lot of sense. SLI remains a relatively rare configuration, used only by enthusiasts, and three- and four-way SLI are rarer still. Substantial gains from such configurations also tend to be somewhat elusive.

Moreover, the high performance graphics world is moving in a direction that puts much more control into the application and depends much less on the display driver and its SLI profiles. Both Vulkan and DirectX 12 are designed to give developers lower-level control that bypasses much of the complexity of the video driver. Explicit multi-adapter support is more flexible than any driver-based SLI and, longer term, should produce better performance. It should also be more widely usable, as it can readily take advantage of GPUs with different performance, and even from different vendors. This makes it possible to, for example, offload post-processing or physics calculations to an integrated GPU while still handling the main graphics workload on a discrete GPU.

Still, we've seen evidence that at least one or two deep-pocketed individuals has bought more than two GTX 1080s under the expectation that they'd be able to connect them together and use them in SLI mode with an enthusiast key. Nvidia probably doesn't have too many of these unsatisfied customers, but those individuals would appear to have a legitimate grievance with the company after its failure to deliver promised functionality.