Fn, short for function, is a modifier key on many keyboards, especially on laptops, used in a compact layout to combine keys which are usually kept separate. It is typically found on laptops due to their keyboard size restrictions. It is also found on many full-sized "multimedia" keyboards as the F-Lock key. It is mainly for the purpose of changing display or audio settings quickly, such as brightness, contrast, or volume, and is held down in conjunction with the appropriate key to change the settings.
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, a box, or different color (usually blue but sometimes orange).
Fn is a modifier key, and works like other modifiers keys, such as Ctrl, Shift and AltGr. For a standard modifier key, the microcontroller inside the keyboard sends a scancode for the modifier itself, which is then interpreted by the operating system and combined with other simultaneous key-presses. The Fn key is a form of meta-modifier key, in that it causes the operating system to see altered scancodes when other keys on the keyboard are pressed. This allows the keyboard to directly emulate a full-sized keyboard, so the operating system can use standard keymaps designed for a full-sized keyboard. However, because the operating system has no notion of the Fn key, the key can not normally be remapped in software, unlike all other standard keyboard keys.
While it is most common for the Fn key processing to happen directly in the keyboard micro-controller, offering no knowledge to the main computer of whether the Fn key was pressed, some manufacturers, like Lenovo, perform this mapping in BIOS running on the main CPU, allowing remapping the Fn key by modifying the BIOS interrupt handler; and Apple, in which the Fn key is mappable and serves other uses too, as triggering the Dictation function by pressing the Fn key twice.
In addition to being mapped to standard keyboard keys like Scroll Lock and Num Lock, the Fn key combinations may also be mapped to control system interfaces to change the LCD brightness, VGA output, or speaker volume on most laptop computers.
Fn and Control key placement
There is not yet an agreed-upon standard for the placement of the Fn key. It is usually placed adjacent to the left Control key, shrinking and displacing it in the process. The control key is most frequently associated with handy modifier keystrokes such as cut-and-paste, or application shortcuts such as control-s to save. The wide control key on a full size IBM PC keyboard layout allows users to become accustomed to using either the left or right side of the key for these shortcuts. In turn, shrinking and displacing it either to the left or the right causes considerable user-annoyance for a set of users.
Further aggravating the situation is the fact that the Fn key is a hardware meta-key which is not remappable through operating system level keyboard remapping tools, However Lenovo ThinkPad systems do allow remapping in the BIOS. One solution, which side-steps the fn and control placement issue, is remapping Caps-Lock as Control. This places Control in an easier to access location to the left of A-key and above the left-shift-key, a location that is favored by some Vim and Emacs users and was used on Unix workstations.
- Most manufacturers today have shrunk and displaced the control key to the lower-left corner of the keyboard, placing Fn to its right. This includes most laptops from HP, Dell, Samsung, and Lenovo Ideapads.
- Lenovo Thinkpads place the Fn key in the lower left, displacing control to the right. However, unlike most other manufacturers, the control key remains an oversize key. Keyboards have been a strong source of loyalty for the brand due to both feel and layout, especially among highly technical users, and Thinkpad keyboards are highly regarded as some of the best laptop keyboards. However, their Fn key placement is sometimes a sticking point for users of other brands.
- Apple Laptops place Fn in the lower-left and shrink control to the right. However, Apple's OS X is somewhat less sensitive to control key shrinking, as it uses the Command-key for many common modifiers, making text-copy the PC keyboard equivalent of Windows-C instead of Ctrl-C.
Control Key Preference Factors
Paramount seems to be whether the user keeps their palm stationary on a wrist rest or not. Other factors include the control key's size, displacement, and position relative to the left-shift key.
A touch typist who prefers to keep their palm resting on a fixed position has difficulty reaching a lower-left control, whereas they can reach a right-displaced control without palm movement. Executing a control-and-shift operation with a right-displaced-control involves curling the little finger slightly underneath the ring-finger. Control key combinations involving the upper-left of the keyboard, including the keys (1, Q, W, 2) require either moving the hand, or using the right-control key with the opposite hand.
A user who hovers their hands and/or moves them laterally may prefer the lower-left control, as combined with movement of the palm, it offers a more open access to the leftmost keys. It also allows control-and-shift operations to be performed without curling the little finger underneath. Some workarounds include using little-finger-shift and ring-finger-control or thumb-control presses. Such change to the point of origin does reduce the useful radius of the first four fingers across the keyboard, yet may be more ergonomic for the hand.
On a fullsize keyboard, some users access the lower-left Control key using the side of their palm, a technique which is not generally possible on shallow throw laptop keyboards with wrist rests.
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