3D Vision Surround In Depth
The concept of “surround” anything is new to Nvidia. In the past, SLI was limited to a single display, so you could have as many as four GPUs in a single PC, but only one monitor served as the output device for all of that horsepower.
Then AMD launched its Radeon HD 5800-series, and by all accounts caught Nvidia flat-footed. For the desktop productivity types, Eyefinity represented a way to expand desktop real estate to three displays from one graphics card. Fans of widescreen 3D gaming saw Eyefinity as an answer to years of wishing. A reference Radeon HD 5870 could viably game across three screens—a situation that improved drastically once AMD enabled CrossFire in Eyefinity mode.
Nvidia’s GF100 GPU employs two display pipelines, so it’s limited to a pair of monitor outputs right out of the gate. Thus, the company makes it possible to support triple-monitor setups through the use of two graphics cards in SLI, giving you a total of four outputs with which to work.
Now, you can use three conventional 60 Hz LCDs like the Dell U2410s on my desk right now, facilitating Surround 2D mode. Or, you can use 120 Hz 3D Vision-compatible displays and projectors to enable 3D Vision Surround—the evolutionary follow-up to 3D Vision, which we reviewed more than a year ago.
How Two Cards Render To Three Displays
Nvidia employs Alternate Frame Rendering (AFR), whether its cards are rendering to one display or three.
In single-display mode, GPU 1 renders the odd-numbered frames, while GPU 2 renders the even-numbered frames. The PCI Express bus and SLI link connector are responsible for getting the result from GPU 2 back to the board where the lone display is connected, yielding a single output.
The inner-workings are similar in Surround 2D mode: GPU 1 renders odd-numbered frames, while GPU 2 renders even-numbered frames. The difference, of course, is that a single frame across three LCDs is much larger—5760x1080, for instance, instead of 1920x1080. Nvidia remains fairly elusive when asked how the engine then outputs to displays attached to two cards, but again, it relates to PCI Express-based transfers and the SLI connector.
Of course, enabling stereoscopic output literally doubles the workload, since each frame now has to be rendered twice (once for each eye). In this case, the first GPU renders odd-numbered frames for the right and left eye, while GPU 2 renders the even-numbered frames for the right and left eye. According to Nvidia, in this way, each GPU is fully saturated at all times.
3D Vision Surround also overrides your v-sync settings, shooting for a constant 120 Hz so that each eye gets 60 frames per second. As a result, the highest frame rate you’ll get in 3D mode is 60 FPS. There is some overhead associated with Nvidia’s AFR technique, and you’ll see evidence of that in our benchmark results that hover around 52 FPS. That’s still plenty playable, though.
