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What is V-Sync (vertical sync)?

In one sentence: Making a game hand new pictures to the screen only between redraws, which stops tearing but can add judder and a little delay.

A little more

V-Sync (vertical sync) makes the game wait for the screen. A finished frame is only swapped in between refreshes, so every refresh shows one whole frame and there is no tearing. If the game is faster than the screen, it waits; if it is slower, the screen shows the previous frame again for one more refresh.

That repeat is what makes a 50 fps game on a 60 Hz screen judder: most frames are shown for one refresh and some for two. Waiting also adds a little input lag, more if frames pile up in a queue. Capping the frame rate at a number that divides the refresh rate (30 or 60 on a 60 Hz screen), or turning on VRR, gives even steps instead.

See it in action

  1. BonusWhy does a game judder when it can't keep up?A screen is a flip book with a thumb that turns the page on a steady beat, and the game is an artist drawing the pages.9 min · interactive

Do it for real

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Related words

  • Screen tearing A line across the picture where the top shows one frame and the bottom the next, because the screen swapped pictures halfway through drawing.
  • VRR (variable refresh rate) When the screen waits for each new picture from the game and redraws right then, instead of on a fixed beat, so there is no tearing or stutter.
  • Input lag The delay between pressing a button and seeing the result on screen, made of the controller, the connection, the game's frames and the screen added together.

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