Nvidia’s new GeForce GTX 1080 graphics cards only support two-way SLI, the company told PC Perspective, drawing back on claims made when the card first launched.
Initially, Nvidia’s plans for creating SLI setups with the latest and greatest GeForce GTX 1080 graphics cards were a bit odd. Two-way configurations were supported using a new high-speed bridge to join the two cards together. Three- and four-way configurations were also promised, but with a twist: first, these would have to use older, slower SLI bridges, and second, system owners would have to generate a special “enthusiast key” to allow access to three- and four-way SLI. Without this key, the system would remain a two-way street.
The plan is simpler now, but for those wealthy individuals hoping to build the very fastest systems imaginable, slightly worse. Two-card configurations that work in SLI using the new bridges will continue to be supported, but the company no longer plans to expand to three- and four-way configurations, and the “enthusiast key” system is being dropped.
Applications that explicitly support multiple individual GPUs, either by taking advantage of DirectX 12’s explicit multi-adapter capabilities or by using APIs such as OpenCL and CUDA for GPU-based computation, 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, can only be scaled up to two cards. Any additional GPUs will remain unused, with one minor exception: Nvidia says a future version of its drivers will allow three- and four-way configurations in certain benchmark applications, including 3DMark. All other SLI profiles are limited 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. Significant benefits of such configurations are also somewhat elusive.
In addition, the high-performance graphics world is moving in a direction that puts much more control into the application and is much less dependent on the display driver and its SLI profiles. Both Vulkan and DirectX 12 are designed to give developers a lower level of control that bypasses much of the complexity of the video driver. Explicit support for multiple adapters is more flexible than any driver-based SLI and should provide better performance in the long run. It should also be more versatile, as it can easily take advantage of GPUs of different performance, and even from different vendors. This makes it possible, for example, to offload post-processing or physics calculations to an integrated GPU, while the main graphics workload is still performed on a separate GPU.
Still, we’ve seen evidence that at least one or two individuals with deep pockets bought more than two GTX 1080s expecting to 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 dissatisfied customers, but those individuals seem to have a legitimate complaint against the company after it failed to deliver the promised functionality.