V-Sync - Something You Don't Know

The story begins when you open FIFA 2010 and play, you see the term "FPS 80" on the top of the screen then the number jump continuously and you don't know what the matter means. That raises a problem that every gamer should know about their VGA, V-sync matter.

For short, V-sync stands for Vertical Sync or Vertical Synchronization which is primarily required because of the physical limitations of CRT monitor when synchronization of frame changes happens with the vertical blanking interval.

Every screen has its own Refresh rate which is calculated in Hertz. It is the number of times screen change in one second. If your Refresh Rate is 60Hz, you would know that in one second, your screen changes 60 times to produce the image (what you see on the screen - whatever static or dynamic image)

It is when you play game which raise the problem. For example, the Refresh rate of your screen is set as 60Hz but the number appearing in game screen is 80, the difference is 20 FPS (frame per second). That is what we call "asynchronism". At the time, we can see the aliasing effect or shadow in game play. It happens when the FPS of the game is too high, and the screen cannot refresh in time.

That leads to the born of Double-buffering. Basically, it have two buffering layer. When screen refresh, the first layer - frame buffer has the function of displaying on-screen images, the second called back buffer will load images in advance then copy the images to the first one.

However, the copy process still waste much time. If the screen refresh immediately in the process, there are still low-quality images with aliasing.

V-sync goes it own way to synchronize FPS of games so that its maximum is equal to the fresh rate of your screen. In the situation above, FPS never exceed 60, which is when you play games with smooth and nice images. V-sync stop back buffer from copying frame buffer until the screen refresh, which avoid delay or traffic jam in constant copy process.

Conversely, when the Refresh rate is 75Hz but the game is set to 50FPS, your VGA can just give 2/3 number of frames of the next image.

Concretely, in the first refresh stage, the initial image (A) is copied to the frame buffer, 2/3 of the second image (B) is brought to the back buffer. In the second refresh stage, the frame buffer still presents the previous image (A) since the 1/3 of the remain (B) is load into back buffer in order that it matches with the last 2/3 of B (loaded before) to create a perfect image B. Then the image B has to wait to the end of this second refresh for the copy to frame buffer... The third refresh goes with the same process and after the fourth, two images are displayed. That is why we can see the game run in 37.5 FPS when Refresh rate is 75Hz.

Hence, V-sync only works in games in which FPS run higher than actual refresh rate to avoid blind shadow or aliasing mode...

Also, Triple-Buffering is a new-born technique as well to fix the drawback of V-sync and Double-buffering. It rules to create a new back buffer for the last 1/3 of the image to be load into the frame buffer right after. Yet, many games don't support this function and it will reduce the performance and consume much more memory to operate.

From those comment above, gamers should pay more attention to performance options and video setting when they play games because the confliction between the hardware (VGA) and the requirements of the games can get your computer down. It is really essential to understand and carry out optimizing the video setting as well as upgrading computer configuration.

Michael Doan is working for a company that provides IT outsourcing services including application development and software outsourcing. If you want to know more about his work, visit the website software outsourcing to see how he can optimize your business.

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