Let’s shed some context: before G-Sync, it was often assumed by the OS/API/Driver that monitors had a fixed frequency. They vary, but 60HZ or 70Hz are quite common values. Because these values are a lowest common denominator, a higher performing frequency would basically be ignored and your monitor would be under-utilized basically. G-Sync can talk directly to the monitor and figure out what the maximum frequency is, and use it.
Normally, graphics rendering is synchronized with the display refresh so that the monitor shows one image per frame (refresh cycle). It is possible for the rendering to go faster than the screen refresh by disabling the Vertical Synchronization (V-sync, or Vertical Sync). What happens then is that while the monitor is displaying a frame, the rendering changes from underneath it, resulting in what’s called “tearing” here is an illustration:
G-Sync raises the ceiling for the maximum vertical sync speed, thus enabling faster FPS, without visible tearing. Your monitor is used at its maximum potential, while avoiding any artifacts. NVIDIA didn’t have a white paper available, but I suspect that G-Sync can also change the frequency of the screen on the fly so that it can match the monitor refresh rate with the game’s FPS. That is really key to the whole thing, since raising the refresh rate does not completely solve issues typically involved with vertical sync.
To make their point, NVIDIA has gathered the endorsement of three of the most high-profile developers in the real-time 3D rendering world: John Carmack (ID Software), Tim Sweeney (Epic Games) and Johan Andersson (DICE).
“The huge gains in GPU rendering power over the past decade have enabled developers and artists to create increasingly complex 3D scenes and worlds. But even on the highest end PC, the illusion of reality is hampered by tearing and stutter. NVIDIA G-SYNC elegantly solves this longstanding problem. Images on a G-SYNC display are stunningly stable and lifelike. G-SYNC literally makes everything look better.” (Tim Sweeney)
“NVIDIA’s G-SYNC technology is a truly innovative solution to an ancient legacy restriction with computer graphics, and it enables one to finally see perfect tear-free pictures with the absolute lowest latency possible. The resulting output really allows your mind to interpret and see it as a true continuous moving picture which looks and feels fantastic. It’s something that has to be seen to be believed!” (Johan Andersson)
“With G-SYNC, you can finally have your cake and eat it too – make every bit of the GPU power at your disposal contribute to a significantly better visual experience without the drawbacks of tear and stutter.” (John Carmack)