The delete
control character
In computing and telecommunication, a control Character (computing), character or non-printing character (NPC) is a code point (a number) in a character encoding, character set, that does not represent a written symbol. They are used as in-band ...
(also called DEL or rubout) is the last character in the
ASCII
ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because of ...
repertoire, with the code
127. It is supposed to do nothing and was designed to erase incorrect characters on
paper tape
Five- and eight-hole punched paper tape
Paper tape reader on the Harwell computer with a small piece of five-hole tape connected in a circle – creating a physical program loop
Punched tape or perforated paper tape is a form of data storage ...
. It is denoted as in
caret notation
Caret notation is a notation for control characters in ASCII. The notation assigns to control-code 1, sequentially through the alphabet to assigned to control-code 26 (0x1A). For the control-codes outside of the range 1–26, the ...
and is in
Unicode
Unicode, formally The Unicode Standard,The formal version reference is is an information technology Technical standard, standard for the consistent character encoding, encoding, representation, and handling of Character (computing), text expre ...
.
Terminal emulators may produce DEL when key or or are typed.
History
This code was originally used to mark deleted characters on
punched tape
Five- and eight-hole punched paper tape
Paper tape reader on the Harwell computer with a small piece of five-hole tape connected in a circle – creating a physical program loop
Punched tape or perforated paper tape is a form of data storage ...
, since any character could be changed to all ones by punching holes everywhere. If a character was punched erroneously, punching out all seven bits caused this position to be ignored or deleted. In
hexadecimal
In mathematics and computing, the hexadecimal (also base-16 or simply hex) numeral system is a positional numeral system that represents numbers using a radix (base) of 16. Unlike the decimal system representing numbers using 10 symbols, hexa ...
, this is 7F to rub out 7 bits (
FF to rubout 8 bits was used for 8-bit codes). This character could also be used as padding to slow down printing after newlines, though the all-zero
NUL was more often used.
The
Teletype Model 33
The Teletype Model 33 is an electromechanical teleprinter designed for light-duty office use. It is less rugged and cost less than earlier Teletype machines. The Teletype Corporation introduced the Model 33 as a commercial product in 1963 after ...
provided a key labelled to punch this character (after the user backed up the tape using another button), and did not provide a key that produced the
Backspace character
Backspace () is the keyboard key that originally pushed the typewriter carriage one position backwards and in modern computer systems moves the display cursor one position backwards,"Backwards" means to the left for left-to-right languages. delete ...
(BS). Therefore, a number of less-expensive computer systems that used Teletypes used this key (and thus the Delete code) to ignore the previous mis-typed character. Video terminals designed to replace the teletype then had to place a key that produced this code where Backspace would be expected, in particular in products from
Digital Equipment Corporation
Digital Equipment Corporation (DEC ), using the trademark Digital, was a major American company in the computer industry from the 1960s to the 1990s. The company was co-founded by Ken Olsen and Harlan Anderson in 1957. Olsen was president unt ...
. On
VT100
The VT100 is a video terminal, introduced in August 1978 by Digital Equipment Corporation (DEC). It was one of the first terminals to support ANSI escape codes for cursor control and other tasks, and added a number of extended codes for special f ...
compatible terminals, this is the character generated by the key labeled . On later terminals, such as the
VT510
The VT520 is an ANSI standard computer terminal introduced by Digital Equipment Corporation (DEC) in 1993 and 1994. The VT520 is a multi-session monochrome text-only terminal with a built-in 14" monitor. The VT510 was a single-session version, whi ...
, the key is labeled (called backarrow in the manual) and by default sent DEL, but could be set up to send BS.
Other terminals designed for systems that did not have a history of using Teletypes would usually make a key at this position send BS, leading to much confusion. Unix, in particular, had an annoying problem in that it could only be programmed to erase the previous character for ''one'' of these (not both), thus requiring the user to reconfigure the terminal driver for each brand of terminal. Depending on the type of terminal the designer used, software would sometimes make the shortcuts or do something, even though these sent the same code as BS and DEL, assuming the backspace key was sending the other code.
A key marked that sends BS is by far the most common on modern terminals and emulators. To make sure they don't delete backwards, the key marked "Delete" on many terminals does not send DEL and instead sends an
escape sequence
In computer science, an escape sequence is a combination of characters that has a meaning other than the literal characters contained therein; it is marked by one or more preceding (and possibly terminating) characters.
Examples
* In C and man ...
such as
^
__Current_use_
.
__Current_use_
Unix-like">3~
.
__Current_use_
Unix-like_operating_systems_can_still_use_it_as_the_stty.html" ;"title="Unix-like.html" ;"title="3~.
Current use
Unix-like">3~.
Current use
Unix-like operating systems can still use it as the stty"> character, i.e., to delete the previous character in the line mode. The terminal driver still cannot be programmed to take both this and Backspace: one must be chosen. However, most modern programs bypass this and use libraries such as readline which accepts both codes. Most Unix terminal emulator
A terminal emulator, or terminal application, is a computer program that emulates a video terminal within some other display architecture. Though typically synonymous with a shell or text terminal, the term ''terminal'' covers all remote termin ...
s can be configured to send either Delete or Backspace when the backspace key is pressed.
DOS
DOS is shorthand for the MS-DOS and IBM PC DOS family of operating systems.
DOS may also refer to:
Computing
* Data over signalling (DoS), multiplexing data onto a signalling channel
* Denial-of-service attack (DoS), an attack on a communicat ...
/Windows
Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for serv ...
never used this character in any way. The BIOS keyboard driver produced Backspace when the backspace key was typed and NUL with scan code 0x53 when the delete key was typed. In Windows the delete key maps to VK_DELETE (0x2E). EGA/VGA fonts, as fonts used by Win32 console
Windows Console is the infrastructure for console applications in Microsoft Windows. An instance of a Windows Console has a screen buffer and an input buffer. It allows console apps to run inside a window or in hardware text mode (so as to oc ...
, usually have the "house" symbol ⌂ at 127 (0x7F) code point, see Code page 437 for details. However, its legacy can be seen in parts of the Windows operating system: as an example, in Microsoft Notepad
Windows Notepad is a simple text editor for Windows; it creates and edits plain text documents. First released in 1983 to commercialize the computer mouse in MS-DOS, Notepad has been part of every version of Windows ever since.
History
In May ...
used to insert the delete character until it was changed in 2018 to make it delete the previous word.
See also
* Eight Ones EO, or Eight Ones, is an 8-bit EBCDIC character code represented as all ones (binary 1111 1111, hexadecimal FF). It is used for synchronisation purposes, such as a time and media filler.
When translated from the EBCDIC character set to code ...
* Backspace
Backspace () is the keyboard key that originally pushed the typewriter carriage one position backwards and in modern computer systems moves the display cursor one position backwards,"Backwards" means to the left for left-to-right languages. delete ...
References
{{reflist
Control characters
Text user interface
History of computing