What is VSync count in Unity3D?

Question

What is the theoretical concept of VSync, and how does it affect rendering?

Answer 1

Monitors refresh pixels in various ways, but they're not all updated at the same time. Old screens for example, used to refresh the pixels one line at a time, top to bottom.

The problem occurred if it was halfway down the screen when it got the new image and simply continued with that. You then had the top half of the screen using the previous frame, while the bottom half of the screen was using the new frame. VSync prevents this by making sure updates are made between refreshes, not during.

This isn't really a problem any longer with modern screens.

If you'd like to read up on VSync here's some helpful wikipedia articles: http://en.wikipedia.org/wiki/Vertical_synchronization and http://en.wikipedia.org/wiki/Screen_tearing