Enter FreeSync And G-Sync
Although a variable refresh-rate standard had long existed for the mobile market (mostly for power-saving benefits), Nvidia was the first to realize the potential of introducing variable refresh rates to desktop gaming-oriented LCDs. The company's solution launched as a proprietary "closed" system dubbed G-Sync. AMD followed suit by announcing "FreeSync," which hinged on an optional standard by VESA under the name "Adaptive-Sync".
The main difference between FreeSync and Adaptive-Sync is that Adaptive-Sync is, strictly speaking, just a DisplayPort protocol addition, whereas FreeSync involves the whole render chain (GPU, DisplayPort protocol and display). It would be correct to say that Adaptive-Sync is a component of FreeSync, or that FreeSync builds and expands upon Adaptive-Sync.
Both AMD's FreeSync and Nvidia's G-Sync operate by manipulating some features of the DisplayPort stream to enable a variable Vblank interval that, in turn, results in a variable refresh rate.
One key difference between FreeSync and G-Sync is that Nvidia actually went through the process of designing a custom LCD scaler (based on an expensive component called a field-programmable gate array or FPGA), whereas AMD entered into agreements with leading scaler manufacturers to support FreeSync in their future products. This difference is very important. The broad implication is that Nvidia will have tighter control of G-Sync's operation, but needs to price its solution higher than AMD's. Because of the components involved, G-Sync displays cost, and will likely continue to cost, $150 to $200 more than their AMD counterparts.
Because of the way FreeSync was established, AMD has little control over how display manufacturers implement the technology. This led to initial quality control issues, such as the flicker many users reported when using the DisplayPort cable and firmware provided with Acer's XG270HU. Apparently, these issues were fixed by the latest display firmware.
To help mitigate problems like that, AMD said it established a QC process to determine how displays become eligible for the FreeSync brand/logo. Unfortunately, AMD declined to disclose what quality standards will be used to establish a "pass" for display manufacturers. You'll have to take AMD's word that future FreeSync-branded monitors will not demonstrate flickering or artifacts, but you'll still need to take up any issues with the display manufacturer.
To be fair, we should note that G-Sync is not entirely flicker-free either. The most annoying limitation right now with both FreeSync and G-Sync is the flickering in menu and loading screens. Try playing Pillars of Eternity with either technology enabled. It's not fun. Hopefully, future driver updates mitigate the artifacts for both vendors.
We covered Nvidia's G-Sync technology extensively in an earlier article: G-Sync Technology Preview: Quite Literally A Game Changer. Today, we'll go over FreeSync in detail and highlight how it differs from G-Sync.
If you'd like to see a proper blind test of the two technologies, I'd also encourage you to read our testing event, AMD FreeSync Versus Nvidia G-Sync: Readers Choose.