What is VSync?

[vkadurin]

I know that it limits the FPS produced by the GPU (or something like that) to the refresh rate of your monitor? What i want to know is how it actually works. 

[Hyydrah]

Here's a helpful article: http://hardforum.com/showthread.php?t=928593

[Raj8396]

Ok it deos limit the fps but not in the way you are thinking.

Some Terminology you will need to know

There are two buffers(place where frames are stored) back buffer is where the frame gpu draws is stored and frame buffer is where the monitor takes frames from.

How moniter displays a frame

So every frame is copied from back buffer to frame buffer in order to give the frame to monitor.

How tearing occurs

The problem of tearing occurs when the monitor refreshes and there is half or two-third (or any kind of unfinished frame) in the frame buffer.

How VSync works

What vsync does is create a rule that new frames can only be copied to the frame buffer right after the monitor refreshes so now there is always a complete frame in the frame buffer so there will be no tearing.

Disadvantage

But when you slow down the gpu by this method it can only run at a fps which is a factor of the refresh rate of the monitor (60Hz monitor you can run at 60,30,20,15,12,etc). So you will not see tearing now but when the fps of your game goes below the refresh rate when you are in a intense situation there drop would be very big from 60 it will go directly to 30fps then to 20. that is the disadvantage of vsync.

Solution

What nvidia has done with there 600series is adaptive vsync it turns the vsync off when you go below the refresh rate and turns it on when you go above it, so its the best of both worlds

i hope you understood :) if you want more detailed explaination go here http://goo.gl/h8UDS