Input lag

In video games, input lag is either the delay between the television or monitor receiving a signal and it being displayed on the screen (see display lag below), or the delay between pressing a button and seeing the game react.

In electronic hardware development, input lag is the delay between an electronic input signal being generated (pressing a button as above) and processed (I/O ports have been read, and memory updated to reflect the state of the input). In this field, the phenomena detailed below, are referred to as Output Lag. More formally, the terms 'Input Latency' and 'Output Latency' are also used. Due to gamers being largely unaware of the phenomenon of input lag at this low level, the terms input lag and output lag became confused over time, and the above description, where input and output lag are combined into a singular phenomenon known as input lag, has become popular.

Overall, the correct terminology is clear - A delay between a physical input occurring (e.g., I/O pin voltage change) and it being processed electronically (I/O pins read by processor and memory registers updated to reflect the state of the pins) is input lag, and a delay between an electronic output being sent (e.g., memory register set to reflect the desired state of an output) and it being processed into a physically observable phenomenon (e.g., memory register read and I/O pin voltage modified accordingly), is output lag. In short, Input Lag occurs on input devices, Output Lag occurs on output devices.

The following are descriptions based on the colloquial use of the term, as used by gamers.

The potential causes for "input lag"- according to the second definition- are described below (steps which have negligible contributions to the input lag have been omitted). Each step in the process increases "input lag", however the net result may be unnoticeable if the overall "input lag" is low enough.

For wired controllers, this lag is negligible. For wireless controllers, opinions vary as to the significance of this lag. Some people claim to notice extra lag when using a wireless controller, while other people claim that the 4-8 milliseconds of lag is negligible.

Since the game requires information on the location of other players, there is sometimes a delay as this information travels over the network. This occurs in games where the input signals are "held" for several frames (to allow time for the data to arrive at every player's console/PC) before being used to render the next frame. At 25 FPS, holding 4 frames adds 160 ms to the overall input lag. However, very few modern online games use this method. The view angle of every modern AAA shooter game is completely unaffected by network lag, for example. In addition, lag compensating code makes classification a complex issue.

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