
Originally Posted by
TweakGuides.com
VSync: Video Synchronization (VSync) is the synchronization of your graphics card and monitors' abilities to redraw an image on the screen a number of times each second, measured in Hz. Your monitor will have a maximum rating in Hz for each resolution (e.g. 1280x1024 at 85Hz). When VSync is enabled (ticked), your graphics card will synchronize with your monitor and only display whole frames - this means your maximum FPS will be capped at your monitor's maximum refresh rate at your chosen resolution, and more importantly in some areas your FPS may drop by as much as 50% if the graphics card has to wait to display a whole frame. Thus enabling VSync can have a major negative performance impact.
By disabling VSync, not only do you uncap your maximum FPS, your overall FPS will also improve as your graphics card no longer has to wait to synchronize with the monitor before display each frame. This may result in some image 'tearing' (i.e. the top and bottom portions of the screen may go slightly out of alignment), however this is totally harmless and usually not very noticeable. Note that you should check your graphics card's control panel for the VSync setting there and make sure it is set to 'Application preference' (or similar) to allow this setting to work correctly.