Vsync is the short version of Vertical Synchronization. Vsync basically refers to an execution option of a video card. This option helps prevent a video card from shifting its display memory till the ongoing refresh cycle on the monitor is completed. Application of vsync matches the executing engine to the monitor’s extreme refresh rate. This happens where the frame rate being generated is much more than a monitor’s refresh rate. This process is effective in throttling the extreme frames produced each second on the graphics card. Vertical sync is therefore responsible for harmonizing video output of a graphics card with the monitor’s refresh rate. Vsync is often needed when a CRT monitor experiences physical limitations. This type of monitor needs to consistently light up the phosphors found on the screen numerous times each second to sustain an image. It can only manage to do so several times each second depending on the rate of electron gun movement in the monitor.
Every time the screen is redrawn entirely, there is movement of electron gun within the monitor. This movement starts at the bottom of a screen to its left side as it prepares to repaint lines in the screen starting from the top left to the bottom and back for another refresh. The period within which electron gun movement happens towards the screen top for a refresh is known as vertical blanking interval. When vsync is enabled, it allows communication to the graphics card resulting to synchronization of actions within the monitor. This implies that a graphics card only swaps the frame buffer then sends a new frame to a CRT monitor as soon as it is set to repaint another new screen which is during the vertical blanking interval. The monitor and the graphics need not to be synchronized and still function well even when the vsync is disabled. However, a disabled vsync can lead to a phenomenon known as tearing in period. This occurs when a graphics card and a CRT monitor are out of sync because both are operating without any concern of each other’s boundaries.