Fn key can also refer to the function keys on a computer keyboard.

Fn is a modifier key on PC keyboards used in a compact layout to combine keys which are usually kept separate. It is typically found on laptops, since a full sized keyboard would be difficult to fit in a laptop chassis.

Compact layouts

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Typically, in a compact layout the main area of the keyboard (containing the letter keys) is kept in much the same layout as with a full-sized keyboard, and the numeric keypad is moved to share a group of central keys. This allows typists to enter text without having to learn a new layout. The symbol that is accessed through pressing Fn is often printed on the key in a smaller font or different colour.

This 78-key UK layout is taken from the Apple iBook. Characters in blue are accessed through the Fn key.

Technical details

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Unlike other modifier keys such as Shift or AltGr, the control processor inside the keyboard typically sends out a different keycode depending on whether the Fn key is depressed. This allows the keyboard to emulate a full sized keyboard and means that specialised keymaps do not need to be created; the operating system can use standard keymaps designed for a full sized keyboard.

Computer keys