IBM PC keyboard
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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. The English-language ones all utilise the QWERTY key scheme.
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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 left of the <Enter> key)
- 104-key "Windows" keyboard layout – Windows and Menu key added
- 107-key "Enhanced" keyboard layout – Wake, Sleep, and Power keys added (for power management)
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.
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/requirement for improving user productivity with general office application software, while other slightly more general keyboard additions have become de facto standards after being introduced by certain operating system/GUI software vendors such as Microsoft.
See also: modifier key
From Teletype keyboards
- Shift- select the upper character, or select upper case of letters
- Caps Lock- Selected upper case, or if shift is pressed, lower case of letters.
- Ctrl- shift 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 the print to screen) CTRL-Q is XON (resume printing stopped by CTRL-S).
- Esc- makes an ASCII ESC character. Older software uses it to exit menus or modes.
- Tab- an ASCII Tab character. Moves to the next tab stop.
- ~- Called a tilde, is an accent, backspaced and printed over other letters for non-English languages.
- `- a grave accent, is also backspaced over letters to write non-English languages. The single quote ' is normally used for an acute accent.
- ^ is a caret, another accent for non-English languages.
- * is an asterisk, used to indicate a note, or multiplication.
- _ is an underline, backspaced and overprinted to add emphasis.
- | is a 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".
- There are two types of quotes because typographers in English alternate between them when quotes are nested.
Invented for the PC
- Control-Alt-Delete- restarts the PC. This is intentionally difficult to type accidentally. It was added to the PC to make testing easier. A reset sequence from keyboards was first invented as a cost-saving measure to avoid a reset button on computers (notably on the Apple II and DEC PDP-11).
- Enter- ASCII keyboards had CR or "carriage return"; Enter traditionally means "do it." It usually indicates the end of some text, or that a selection should operate.
- Windows- a quick way to open an overall "Start" menu in Windows (but can usually be configured to do the same thing in Linux). Win-m minimizes everything. Win-r opens the run window. Win-e launches the windows explorer.
- Context menu key - same as right clicking an item with the mouse pointer arrow
- Function keys- the numbered keys, use varies by program, but F1 is often "help."
- Arrow keys- move on the screen. When shifted, they select items.
- Home- move to the start of text, usually the left side of the screen.
- Shift-Home- Varies: modern systems usually move to the start of text, selecting on the way. Many older programs move to the beginning of the document or paragraph.
- End- move to the end of text, usually the right-most edge of the current line.
- Shift-End- Varies: modern systems usually move the end of the line, selecting as they go. Many older programs moved to the end of the paragraph of document.
- page-up, page-down move through the document by pages.
- del delete the character before the screen position, or the selected items.
- ins toggle between "insertion" and "overwrite" mode.
- Shifted tab usually goes backward one tab stop.
- Print screen- originally printed a text image of the screen.
- Ctrl-print screen now customarily places a graphic image of the screen in the cut and paste buffer.
- Num lock- when off, the numeric keypad becomes arrow keys. When on, it is a 10-key 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- 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.
- Pause/Break- CTRL-BREAK traditionally stopped programs.
- Alt- shift 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.
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). The three connector types are listed below in descending chronological order:
- 5-pin DIN (DIN 41524) "AT" connector
- 6-pin "Mini-DIN" (DIN 45322) "PS/2" connector
- 4-pin USB connector
External links
- Standard keyboard layouts (http://www.pcguide.com/ref/kb/layout/std.htm) – From The PC Guide website
- IBM.com keyboard page (http://www-306.ibm.com/software/globalization/topics/keyboards/physical.jsp)