IBM PC keyboard

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Memorial to a keyboard in Yekaterinburg, Russia

The IBM PC keyboard and its derivative computer keyboards are standardized. However, during the 20 years of the PC architecture being constantly updated, several types of keyboards have been developed.

1 Keyboard layouts
2 Standard key meanings
3 Connectors
4 See Also
5 External links

[edit] Keyboard layouts

The following list gives a concise overview of the PC keyboard as it has changed over the years, the changes often being made at the launch of new PC versions. For each layout, some of the most significant updates are mentioned.

83-key PC/XT keyboard layout – original left hand side function key (F key) columns with 10 keys F1 through F10; electronically not compatible with the later keyboard types.
84-key PC/AT keyboard layout – the "84th key" being <SysRq> i.e. System Request; numerical block now clearly separated from main keyboard; also added indicator LEDs for Caps/Scroll/Num lock.
101-key "Enhanced" keyboard layout – additional navigation and control keys; 12 F keys in row along top, grouped F1-4, F5-8, and F9-12.
102-key "Enhanced" keyboard layout – (additional key to the right of the left Shift key for European layouts)
106-key "Enhanced" keyboard layout – 5 more keys added for input in Asian languages.
104-key "Windows" keyboard layout – Windows(x2) and Menu key added.
105-key as above, but for European layouts.
109-key as above, but for Asian layouts.
107-key "Enhanced" keyboard layout – Power management keys were added.

So-called "multimedia keyboards" may offer additional buttons to the 104 or 107 "standard" keys, often providing volume control, media player buttons, and miscellaneous user-configurable shortcuts, e.g. to email clients, web browsers, etc.

[edit] Standard key meanings

The PC keyboard with its various keys has a long history of evolution reaching back to teletypewriters. In addition to the 'old' standard keys, the PC keyboard has accumulated several special keys over the years. Some of the additions have been inspired by the opportunity or requirement for improving user productivity with general office application software, while other slightly more general keyboard additions have become the factory standards after being introduced by certain operating system or GUI software vendors such as Microsoft.

See also: modifier key

[edit] From mechanical typewriters

Shift selects the upper character, or select upper case of letters. The Shift key in typewriters was attached to a lever that moved the character types so that the uppercase characters could be printed in the paper. Unlike mechanical typewriters, PC keyboards do not capitalize all letters properly when both shift keys are engaged simultaneously.
Caps Lock selects upper case, or if shift is pressed, lower case of letters. In mechanical typewriters, it worked like the Shift key, but also used a lock to keep the Shift key depressed. The lock was released by pressing the Shift key.
Enter wraps to the next line or activates the default or selected option. ASCII keyboards were labeled CR or Return. Typewriters used a lever that would return the cylinder with the paper to the start of the line.

[edit] From Teletype keyboards

Ctrl shifts the value of letters and numbers from the ASCII graphics range, down into the ASCII control characters. For example, CTRL-S is XOFF (stops many programs as they print to screen) CTRL-Q is XON (resume printing stopped by CTRL-S).
Esc produces an ASCII escape character. It may be used to exit menus or modes.
Tab produces an ASCII Tab character. Moves to the next tab stop.
~ is the tilde, an accent backspaced and printed over other letters for non-English languages. Nowadays the key does not produce a backspaceable character and is used for 'not' or 'circa'.
` is a grave accent or backtick, also formerly backspaced over letters to write non-English languages; on some systems it is used as an opening quote. The single quote ' is normally used for an acute accent.
^ is a circumflex, another accent for non-English languages. Also used to indicate exponentiation where superscript is not available.
* is an asterisk, used to indicate a note, or multiplication.
_ is an underscore, backspaced and overprinted to add emphasis.
| is a vertical bar, originally used as a typographic separator for optical character recognition. Many character sets break it in the middle so it cannot be confused with the numeral "1" or the letter "l". This character is often known as a pipe.

[edit] Invented for the PC

The Windows key is a quick way to open the Start menu in Windows' standard Explorer shell, and can usually be configured to behave similarly in other graphical user interfaces, for Windows and other operating systems.
The menu key brings up a context menu, similar to right-clicking.
Function keys are the numbered keys, use varies by program, but F1 is often "help."
Arrow keys move on the screen. When shifted, they select items.
Home moves to the start of text, usually the left side of the screen.
End moves to the end of text, usually the right-most edge of the current line.
PgUp and PgDn move through the document by pages.
Delete deletes the character before the screen position, or the selected items.
Insert toggles between "insertion" and "overwrite" mode.
Print screen originally printed a text image of the screen; nowadays often takes a screenshot. In combination with Alt, it produces a different keycode, SysRq.
Num lock toggles between states for the numeric keypad. When off, it acts as arrow and navigational keys. When on, it is a 10-key pad similar to a standard calculator. Preferences vary so much that a favorite default for this key can often be configured in the BIOS configuration. Its continued existence on keyboards that separate out the arrow keys has mostly historical reasons.
Scroll lock is little-used. On modern software, typing text usually causes earlier text to scroll off the top of the screen or window. Some old programs could disable this and restart at the top of the window when scroll lock was pressed. The advantage is that the entire screen full of text does not shift, making it easier to read. It was also used to lock the cursor on its line and scroll the work area under it. On spreadsheets such as Microsoft Excel, it locks the cell pointer on the current cell, allowing the user to use the arrow keys to move the view window around without moving the cell pointer.
Pause pauses either output or processing. In combination with Control, it produces a different keycode, for Break. Ctrl-Break traditionally stopped programs in DOS. Ctrl-Break is also used to halt execution of the debugger in some programming environments such as Microsoft Visual Studio. In combination with the Windows key, it brings up the System Properties window in Microsoft Windows environments.
Alt shifts the letters and numbers into the range above hex 0x80 where the international characters and special characters exist in the PC's standard character set. Alt plus a number typed on the numeric pad produces special characters, see Windows Alt keycodes.
AltGr works like the Ctrl+Alt key combination, often used to print special characters like the backslash on non-english keyboards. (On the original IBM AT Enhanced keyboard the right Alt key has green letters).
Fn may be present on compact keyboards such as those built into laptop computers. When depressed in combination with other keys, it either enables the user to access key functions that do not have dedicated keys on the compact keyboard (such as the numeric block), or it controls hardware functions such as switching between the built-in screen and an external display, changing screen brightness, or changing speaker volume. These alternate meanings are usually indicated with text or symbols of a different color printed on the key, with the 'Fn' key text having that same color.

[edit] Connectors

There are three types of connector used to connect a PC keyboard to the main system unit. All three are mechanically different from each other, but the first two are electrically identical (except for XT keyboards, which used a connector mechanically identical to the later AT connector, but not electrically compatible with it). The three connector types are listed below in chronological order: