G-SYNC monitors have a special chip installed in them that replaces the regular scaler.

It allows the monitor to change its refresh rate dynamically — according to GPU’s frame rates (Hz=FPS), which in turn eliminates screen tearing and stuttering as long as your FPS doesn’t exceed the monitor’s maximum refresh rate.

Unlike V-Sync, though, G-SYNC does not introduce a significant input lag penalty.

In addition, a dedicated G-SYNC module offers variable overdrive. Gaming monitors use overdrive to push their response time speed so that the pixels can change from one color to another fast enough to prevent ghosting/trailing behind fast-moving objects.

However, most monitors without G-SYNC don’t have variable overdrive, but only fixed modes; for instance: Weak, Medium and Strong. The problem here is that different refresh rates require different levels of overdrive.

Now, at 144Hz, the ‘Strong’ overdrive mode might perfectly eliminate all trailing, but it also might be too aggressive if your FPS drops to ~60FPS/Hz, which will cause inverse ghosting or pixel overshoot.

For optimal performance in this case, you would need to manually change the overdrive mode according to your FPS, which isn’t possible in video games where your frame rate fluctuates a lot.

G-SYNC’s variable overdrive can change on the fly according to your refresh rate, thus removing ghosting at high frame rates and preventing pixel overshoot at lower frame rates.