Backspace

File:Backspace.jpg

A backspace key

Backspace (Template:Keypress, Template:Keypress) is the keyboard key that in typewriters originally pushed the carriage one position backwards. In modern computer systems, it typically moves the display cursor one position backwards,Template:Efn deletes the character at that position, and shifts back any text afterTemplate:Efn that position by one character.

Nomenclature

File:Blickensderfer model 7, 1909.jpg

An early typewriter with a backspacer[sic] key. (Blickensderfer Model 7)

Although the term "backspace" is the traditional name of the key which steps the carriage back and/orTemplate:Efn deletes the previous character, the actual key may be labeled in a variety of waysTemplate:Mdashfor example delete, erase,Template:Efn or with a left pointing arrow. Some very early typewriters labeled this key the backspacer key. A dedicated symbol for "backspace" exists as Template:Unichar but its use as a keyboard label is not universal.

File:Hemingway Corona number 3 typewriter.jpg

Corona #3 typewriter. Note the oddly positioned backspace key, located off the keyboard, towards the back of the machine, on the right.

Backspace is distinct from the delete key, which in a teletypewriter would punch out all the holes in punched paper tape to strike out a character, and in modern computers deletes text at or following the cursor position. Also, the delete key often works as a generic command to remove an object (such as an image inside a document, or a file in a file manager), while backspace usually does not. Full-size Mac keyboards have two keys labeled delete; a key that functions as a backspace key, and a key that functions as a delete key. Smaller Mac keyboards, such as laptop keyboards, have only a key that functions as a backspace key. Full-size PC keyboards have a backspace key (in the main section) and two delete keys (in the extended area).

Combining characters

With some typewriters,Template:Efn a typist would, for example, type a lowercase letter A with acute accent (á) by typing a lowercase letter A, backspace, and then the acute accent key. This technique (also known as overstrike) is the basis for such spacing modifiers in computer character sets such as the ASCII caret (^, for the circumflex accent). Backspace composition no longer works with typical modern digital displays or typesetting systems.Template:Efn It has to some degree been replaced with the combining diacritical marks mechanism of Unicode, though such characters do not work well with many computer fonts, and precomposed characters continue to be used. (Some software like TeX or Microsoft Windows use the opposite method to apply a diacritical mark, namely typing the accent first, and then the base letter to be accented.)

Use in computing

Common use

In modern systems, the backspace key is often mapped to the delete character (127₁₀, 7f₁₆, DEL in ASCII), although the backspace key's function of deleting the character before the cursor remains. In computers, backspace can also delete a preceding newline character, something generally inapplicable to typewriters.

IBM PC keyboard (Windows, ANSI US layout)
Esc		F1	F2	F3	F4		F5	F6	F7	F8		F9	F10	F11	F12		PrtScn/ SysRq	Scroll Lock	Pause/ Break
																	Insert	Home	PgUp		Num Lock	∕	∗	−
																	Delete	End	PgDn		7	8	9	+
																					4	5	6
																		↑			1	2	3	Enter
																	←	↓	→		0    Ins		.  Del

^H

Template:See Pressing the backspace key on a computer terminal would generate code 08₁₀, the ASCII control code BS (Backspace), which would delete the preceding character. That control code could also be accessed by pressing Template:Keypress+Template:Keypress, as H is the eighth letter of the Latin alphabet. Terminals which did not have the backspace code mapped to the function of moving the cursor backwards and deleting the preceding character would display the symbols ^H (caret, H) when the backspace key was pressed. Even if a terminal did interpret backspace by deleting the preceding character, the system receiving the text might not. Then, the sender's screen would show a message without the supposedly deleted text, while that text, and the deletion codes, would be visible to the recipient. This sequence is still used humorously for epanorthosis by computer literates, denoting the deletion of a pretended blunder, much like a strikethrough; in this case, however, the ^H symbol is faked by typing a regular '^' followed by typing a regular 'H'.

Example:

Be nice to this fool^H^H^H^Hgentleman; he's visiting from corporate HQ.