Vertical synchronization (v-sync, vbl-sync) refers generally to the synchronization of frame changes with the vertical blanking interval. Since CRTs were nearly the only common video display technology prior to the widespread adoption of LCDs, the frame buffers in computer graphics hardware are designed to match the CRT characteristic of drawing images from the top down a line at a time by replacing the data of the previous frame in the buffer with that of the next frame in a similar fashion. When the display requests current contents of the frame buffer before the current frame is done being written on top of the previous one, the frame buffer gives it the current mishmash of both frames, producing a page tearing artifact partway down the image.

Vertical synchronization eliminates this by timing frame buffer fills to coincide with the display's data requests, thus ensuring that only whole frames are seen on-screen.

Computer games and other advanced programs often allow vertical synchronization as an option, but it is sometimes disabled because it often has the effect of hampering performance on slower hardware (and/or in programs that were not adequately designed for v-synced operation) to the point where frame rates drop below that of the display hardware.