Keyboard

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" (in most EBCDIC codepages, vertical bar and divided vertical bar are separate characters). This character is often known as a "pipe" or a "fencepost.