Fn key

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Function (Fn) key on a typical notebook computer
Function layer legends (cyan) on an Acer notebook computer

The function key, universally labelled "Fn", is a hardware-level modifier key. The function key is read directly by the keyboard controller, and it allows a single key on the keyboard to double up as multiple keys, or to send commands to the keyboard controller directly. The operating system is never aware of the existence of the function key; for a laptop where Fn+F12 maps to print screen, the keyboard controller detects the function key and transmits a print screen keypress to the computer as if the keyboard had a physical print screen key. Programs such as AutoHotkey cannot be used to block or remap the function key as a result.

The function key is widely used on laptops to send hardware commands (e.g. screen brightness, display selection) as well as to assist with the restriction on key count on laptops. On some product lines including ThinkPads and Macintosh laptops, the function key is placed at the bottom left, with the control key moved one place to the right. Most laptops place function between control and the left (or only) Windows key for the sake of muscle memory, otherwise the user will struggle with issuing ctrl-based keyboard shortcuts. This is not a serious issue on Macintosh computers as the command key is used to issue shortcuts and the control key is rarely used outside of Terminal.

See also