Screen tearing is a phenomenon in video where a newly rendered frame overlaps a previously rendered frame, creating a torn look as two parts of an object (such as a wall) don't line up. This occurs when the output device sends frames out of sync with the display's refresh rate.
Screen tearing can occur on all display types but is most common with video games and videos decoded and shown by computers, as heavy processing can limit synchronization capabilities. It is less common with other mediums such as DVD players and TVs since the frames are not dynamically generated as they are with computers, but are preset. The frame rate given to the display device is therefore more constant and reliable.
Prevention
Screen tearing can be prevented by altering the device outputting the video or the device displaying it.
V-sync
Vertical synchronization is an option often found on computers. The use of V-sync can prevent screen tearing by only allowing a new frame to be sent after the previous frame has been displayed (i.e. during the vertical blanking interval). This prevents any frames from overlapping which is how screen tearing occurs. Enabling vertical synchronization can result in a lower overall frame rate because of the delay applied to the display of new frames.
Beam tracing
Some graphics systems support beam tracing - copying a back buffer to the front buffer just after the front buffer address has been scanned and displayed on screen. This technique can increase the amount of time available for processing each frame but requires that back buffers are copied and not flipped.
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