V-SYNC is a technique available on most modern graphics cards. It ensures that each frame update is displayed at the same time, or vertically in sync with the screen's refresh cycle.
What about FPS?
FPS is an acronym for "frames per second" - it is the rate at which consecutive rendered frames are displayed on your screen.
Setting VSYNC ON ensures that no more than one frame can be sent to your monitor every 16 milliseconds, but only if the graphics hardware cannot keep up with your current frame rate. When FPS drops below 60, this may result in stuttering or jerks occurring in the display of new frames.
This happens because there are too many unique frames queued up, and they are being played back at a much lower rate than they were created in - thus creating uneven pacing between them (like playing an old 8-bit game at low speed).
To reduce the impact of this phenomenon you should try to maintain a steady high frame rate. This is where VSYNC ON can help - since it caps your FPS to a maximum of 60, you will never have more than one unique frame being shown at the same time - the tears and uneven pacing between frames should be eliminated.
In some cases, however, turning on VSYNC may cause additional problems due to laggy response from the display device (see next section). In those cases, you might want to try disabling it instead.
How does V-SYNC work?
Now, let us imagine a different scenario where your game is running at 60 FPS with V-SYNC enabled. This time the graphics card has to prepare a new frame every 16 milliseconds in order to send it for display. But what if the next frame isn't ready yet?
With V-SYNC enabled this means that two subsequent frames may be displayed within 16 milliseconds of each other, meaning that there is an 8-millisecond gap between them instead of 1 second. In other words, each frame is only displayed for 8 milliseconds before being replaced by the next one.
Frames will start to appear choppy and animation will become very stuttery as you lose more than half of the usual number of frames which should have been displayed during those lost milliseconds.
The majority of games do not have V-SYNC enabled because they are the ones that still rely on double buffering. This means that each frame is actually prepared twice, once to be displayed and once for saving in memory which can be used if there is a shortage of frames ready for display (and thus too long gaps between them).
If you use V-SYNC then this second copy never gets displayed; it is only meant for temporary storage until the next frame becomes available.
What happens without V-SYNC?
With no vertical sync option enabled your graphics card will keep producing new frames as fast as possible, even if they aren't really needed. It's like delivering more presents than requested by your friends; although it does not cost you any extra money, it is not really useful either.
With V-SYNC disabled your game will benefit from the double buffering technique which ensures that each frame is displayed for at least 16 milliseconds before being replaced. This way the gaps between frames are much shorter which produces a perceptibly smoother animation at no additional cost on your graphics card's performance.
There are some very rare cases where tearing can actually be seen as an advantage because it creates a more fluid movement in high motion scenes, even if tearing normally manifests itself as small defects during rapid object moving across the screen. It should also be mentioned here that tearing usually occurs when you have V-SYNC enabled along with Vertical refresh/resync set to "on".
Setting this option to Off will usually prevent the appearance of tearing, although keeping it enabled may sometimes create a smoother animation where objects appear partly at one refresh cycle and partly at the next one. This is normal behavior as long as your FPS never drops below your screen's refresh rate. In this case, you should also make sure that triple buffering is turned on as well which can help reduce tearing further as well as increase performance if it happens to be enabled.
Playability
V-SYNC has benefits when playing games on PC monitors, but can negatively affect the playability of some games when used with regular LCD TVs.
As an example, let us imagine two different scenarios: First, your game runs constantly at 50 FPS (Frames Per Second), with V-SYNC enabled this means the graphics card tries to push out 50 new frames each second to be drawn by the monitor/television.
Each frame is then displayed for 16 milliseconds before being replaced by the next one. This ensures that there is never more than a 1-second difference between each of the frames, producing an even animated scene.
The second scenario is that your game only runs at 30 FPS, but this time with V-SYNC disabled. In this case, the graphics card tries to push out 33 new frames each second to be drawn by the monitor/television. This means there's a difference of 16 milliseconds between each frame when compared with the previous simulation, producing an "unsmooth" animated scene where objects and characters appear to stutter and jerk around between frames (this is known as micro stuttering).
It can be compared best with film; we know that films are not produced in real-time and normally consist of 24 or 25 different images each second but our brain adjusts the frames to make a smooth moving picture. V-SYNC helps ensure this is the case when playing video games, but it can have undesired effects when using a television instead of a PC monitor.
What is adaptive V-SYNC?
Adaptive V-SYNC is a method that allows your video card to use either V-SYNC or triple buffering based on its own performance during gameplay.
When enabled, it helps reduce tearing by ensuring that the refresh rate of your monitor/television will be matched with the updating speed of new frames pushed out by the graphics card. If this option is turned on triple buffering may also be used to minimize stuttering and jerking between frames if needed.
If you are experiencing micro stuttering while playing games with adaptive V-SYNC enabled, try changing your vertical sync settings from "on" to "off". If that does not help then you should strongly consider turning off adaptive V-sync as well since it may make games unplayable due to the previously mentioned micro stuttering.
V-SYNC from different graphic card brands
NVIDIA GeForce graphics cards
These include NVIDIA's Kepler, Maxwell, and Fermi architectures. Adaptive synchronization technology is supported by all of them, but it should be mentioned here that the performance hit from enabling this option can vary depending on your model of graphics card - a GTX 660 for example will not necessarily run as smoothly as a GTX 760 or 970. You may want to experiment with both G-SYNC and adaptive V-SYNC options enabled to see which has the most positive effect on your particular system.
AMD/ATI Radeon graphics cards
This brand uses different techniques depending on the generation of video cards being used: Fusion APUs (2011 models onwards) Work correctly with V-SYNC enabled by default and have no option to enable or disable this feature. V-SYNC is only supported when switching to exclusive fullscreen mode, but not borderless windowed/fullscreen modes. Older GCN 1.1 graphics cards (Graphics Core Next) Require the "LCD Overdrive" control panel feature to be turned on before V-SYNC can function correctly.
This can however reduce the sharpness of textures slightly in some games, so it is recommended that you leave this option off if you plan to use adaptive V-SYNCs also. GCN 1.2+ graphics cards (Graphics Core Next 2 & 3) Optionally require an external program called RadeonPro to configure your synchronization options for these models - see below for links and more information regarding this software.
AMD graphics cards only offer a triple buffering option on some of their video cards, and it works in a slightly different way to V-SYNC on Nvidia's models - instead of trying to synchronize your monitor/television with the output from your graphics card, this option forces data previously rendered by the GPU into system memory (RAM) before sending that increased amount of information to be drawn onto your display.
This can produce similar results to adaptive V-sync but is not recommended unless you experience severe stuttering when using vertical sync (V-SYNC). If you do decide to try triple buffering make sure that you also disable "Enable Vertical Sync" under the 3D settings page in Catalyst Control Center for AMD Radeon graphics cards.
Note: If you have an AMD video card that supports the use of Adaptive V-SYNC or triple buffering then it can be enabled from within Catalyst Control Center (CCC) by going to "My Digital Flat Panels" > "High Definition Content" > "HDMI Properties" and selecting one of these options from the drop-down menu.
You can also enable this option while playing a game by using RadeonPro, a program that is available for free on Steam. It works with all GCN 1.1+ graphics cards and allows synchronization options to be adjusted freely if required, but should only be used if CCC does not offer this feature for your hardware model.
Intel graphic cards
These are the only brand of graphics cards that currently do not support Adaptive V-SYNC. The use of triple buffering is also not supported, so the only way to avoid tearing on Intel's video cards is to adjust your vertical sync setting in-game - if this option is available.
If you have an Intel Iris Pro Graphics model then switching "Vertical Sync" to "Mostly Off" will allow you to use adaptive V-SYNC without experiencing any screen tearing.
Conclusion
The two main disadvantages of vertical sync that have been listed here are a loss of performance and a reduction in stuttering, with the former being more prevalent on systems with lower-powered graphics cards.
Overall however the benefits from using V-SYNC tend to outweigh these issues, especially when paired with higher quality models of monitor or television which can screen tear much more noticeably - especially during gaming. Vertical Sync should only be disabled if you really require an increase in performance at all costs - where stability is not an issue for example."