They don’t have zero latency. It’s a misconception.
The industry standard way to measure screen lag is from the middle of the screen. Let’s say you have a 60Hz display and hit the mouse button to shoot the very moment it’s about to draw the next frame, and the game manages to process the data before the draw starts. The beam would start to draw, and when it gets to the middle of the screen, we take our measurement. That will take 1 / 60 / 2 = 8.3ms.
Some CRTs could do 90Hz, or even higher, but those were really expensive (edit: while keeping a high resolution, anyway). Modern LCDs can do better than any of them, but it took a long time to get there.
They don’t have zero latency. It’s a misconception.
The industry standard way to measure screen lag is from the middle of the screen. Let’s say you have a 60Hz display and hit the mouse button to shoot the very moment it’s about to draw the next frame, and the game manages to process the data before the draw starts. The beam would start to draw, and when it gets to the middle of the screen, we take our measurement. That will take 1 / 60 / 2 = 8.3ms.
Some CRTs could do 90Hz, or even higher, but those were really expensive (edit: while keeping a high resolution, anyway). Modern LCDs can do better than any of them, but it took a long time to get there.