Nvidia has developed the G-SYNC module, built to fit inside a display and work with the hardware and software in most of GeForce GTX GPUs.
With V-SYNC off you can have fast input response time, but images are seriously corrupted by tearing. Or, you can use V-SYNC on, but then games get laggy, and any time the GPU’s FPS falls below the refresh rate of the monitor, animation stutters badly.
With G-SYNC, the monitor begins a refresh cycle right after each frame is completely rendered on the GPU. Since the GPU renders with variable time, the refresh of the monitor now has no fixed rate.