ASCII
MIME / IANA | us-ascii |
---|---|
Alias(es) | ISO-IR-006,[1] ANSI_X3.4-1968, ANSI_X3.4-1986, ISO_646.irv:1991, ISO646-US, us, IBM367, cp367[2] |
Language(s) | English (made for; does not support all loanwords), Malay, Rotokas, Interlingua, Ido, and X-SAMPA |
Classification | ISO/IEC 646 series |
Extensions |
|
Preceded by | ISO/IEC 10646 (Unicode) |
ASCII (/ˈæskiː/ ⓘ ASS-kee),[3]: 6 an acronym for 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 technical limitations of computer systems at the time it was invented, ASCII has just 128 code points, of which only 95 are printable characters, which severely limited its scope. Modern computer systems have evolved to use Unicode, which has millions of code points, but the first 128 of these are the same as the ASCII set.
The Internet Assigned Numbers Authority (IANA) prefers the name US-ASCII for this character encoding.[2]
ASCII is one of the
Overview
ASCII was developed in part from telegraph code. Its first commercial use was in the Teletype Model 33 and the Teletype Model 35 as a seven-bit teleprinter code promoted by Bell data services.[when?] Work on the ASCII standard began in May 1961, with the first meeting of the American Standards Association's (ASA) (now the American National Standards Institute or ANSI) X3.2 subcommittee. The first edition of the standard was published in 1963,[5][6] underwent a major revision during 1967,[7][8] and experienced its most recent update during 1986.[9] Compared to earlier telegraph codes, the proposed Bell code and ASCII were both ordered for more convenient sorting (i.e., alphabetization) of lists and added features for devices other than teleprinters.[9]
The use of ASCII format for Network Interchange was described in 1969.[10] That document was formally elevated to an Internet Standard in 2015.[11]
Originally based on the (modern)
For example, lowercase i would be represented in the ASCII encoding by binary 1101001 = hexadecimal 69 (i is the ninth letter) = decimal 105.
Despite being an American standard, ASCII does not have a code point for the
History
The American Standard Code for Information Interchange (ASCII) was developed under the auspices of a committee of the American Standards Association (ASA), called the X3 committee, by its X3.2 (later X3L2) subcommittee, and later by that subcommittee's X3.2.4 working group (now
With the other special characters and control codes filled in, ASCII was published as ASA X3.4-1963,
The X3 committee made other changes, including other new characters (the
Revisions of the ASCII standard:
- ASA X3.4-1963[3][6][20][22]
- ASA X3.4-1965 (approved, but not published, nevertheless used by
- USAS X3.4-1967[3][7][22]
- USAS X3.4-1968[3][21][22]
- ANSI X3.4-1977[22]
- ANSI X3.4-1986[9][22]
- ANSI X3.4-1986 (R1992)
- ANSI X3.4-1986 (R1997)
- ANSI INCITS 4-1986 (R2002)[24]
- ANSI INCITS 4-1986 (R2007)[25]
- (ANSI) INCITS 4-1986[R2012][26]
- (ANSI) INCITS 4-1986[R2017][27]
In the X3.15 standard, the X3 committee also addressed how ASCII should be transmitted (
Design considerations
Bit width
The X3.2 subcommittee designed ASCII based on the earlier teleprinter encoding systems. Like other
ITA2 was in turn based on Baudot code, the 5-bit telegraph code Émile Baudot invented in 1870 and patented in 1874.[30]
The committee debated the possibility of a
The committee considered an eight-bit code, since eight bits (
Internal organization
The code itself was patterned so that most control codes were together and all graphic codes were together, for ease of identification. The first two so-called ASCII sticks
Many of the non-alphanumeric characters were positioned to correspond to their shifted position on typewriters; an important subtlety is that these were based on mechanical typewriters, not electric typewriters.23456789-
were "#$%_&'()
– early typewriters omitted 0 and 1, using O (capital letter o) and l (lowercase letter L) instead, but 1!
and 0)
pairs became standard once 0 and 1 became common. Thus, in ASCII !"#$%
were placed in the second stick,[a][15] positions 1–5, corresponding to the digits 1–5 in the adjacent stick.[a][15] The parentheses could not correspond to 9 and 0, however, because the place corresponding to 0 was taken by the space character. This was accommodated by removing _
(underscore) from 6 and shifting the remaining characters, which corresponded to many European typewriters that placed the parentheses with 8 and 9. This discrepancy from typewriters led to bit-paired keyboards, notably the Teletype Model 33
Electric typewriters, notably the
/?
pair also dates to the No. 2, and the ,< .>
pairs were used on some keyboards (others, including the No. 2, did not shift ,
(comma) or .
(full stop) so they could be used in uppercase without unshifting). However, ASCII split the ;:
pair (dating to No. 2), and rearranged mathematical symbols (varied conventions, commonly -* =+
) to :* ;+ -=
.
Some then-common typewriter characters were not included, notably ½ ¼ ¢
, while ^ ` ~
were included as diacritics for international use, and < >
for mathematical use, together with the simple line characters \ |
(in addition to common /
). The @ symbol was not used in continental Europe and the committee expected it would be replaced by an accented À in the French variation, so the @ was placed in position 40hex, right before the letter A.[3]: 243
The control codes felt essential for data transmission were the start of message (SOM), end of address (EOA), end of message (EOM), end of transmission (EOT), "who are you?" (WRU), "are you?" (RU), a reserved device control (DC0), synchronous idle (SYNC), and acknowledge (ACK). These were positioned to maximize the Hamming distance between their bit patterns.[3]: 243–245
Character order
ASCII-code order is also called ASCIIbetical order.
- All uppercase come before lowercase letters; for example, "Z" precedes "a"
- Digits and many punctuation marks come before letters
An intermediate order converts uppercase letters to lowercase before comparing ASCII values.
Character set
0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | A | B | C | D | E | F | |
0x | NUL | SOH
|
STX
|
ETX | EOT | ENQ | ACK
|
BEL | BS | HT
|
LF
|
VT
|
FF
|
CR | SO
|
SI
|
1x | DLE
|
DC1
|
DC2
|
DC3
|
DC4
|
NAK
|
SYN
|
ETB
|
CAN | EM
|
SUB | ESC | FS
|
GS
|
RS
|
US
|
2x | SP
|
!
|
"
|
# | $
|
%
|
&
|
'
|
(
|
)
|
*
|
+
|
,
|
-
|
. | / |
3x | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | : | ; | < | =
|
> | ?
|
4x | @
|
A | B | C | D | E | F | G | H | I | J | K | L | M | N | O |
5x | P | Q | R | S | T | U | V | W | X | Y | Z | [
|
\ | ]
|
^
|
_ |
6x | `
|
a | b | c | d | e | f | g | h | i | j | k | l | m | n | o |
7x | p | q | r | s | t | u | v | w | x | y | z | {
|
| | }
|
~
|
DEL |
Changed or added in 1963 version
Changed in both 1963 version and 1965 draft
|
Character groups
Control characters
ASCII reserves the first 32
For example, character 0x0A represents the "line feed" function (which causes a printer to advance its paper), and character 8 represents "
The original ASCII standard used only short descriptive phrases for each control character. The ambiguity this caused was sometimes intentional, for example where a character would be used slightly differently on a terminal link than on a data stream, and sometimes accidental, for example the standard is unclear about the meaning of "delete".
Probably the most influential single device affecting the interpretation of these characters was the Teletype Model 33 ASR, which was a printing terminal with an available paper tape reader/punch option. Paper tape was a very popular medium for long-term program storage until the 1980s, less costly and in some ways less fragile than magnetic tape. In particular, the Teletype Model 33 machine assignments for codes 17 (control-Q, DC1, also known as XON), 19 (control-S, DC3, also known as XOFF), and 127 (delete) became de facto standards. The Model 33 was also notable for taking the description of control-G (code 7, BEL, meaning audibly alert the operator) literally, as the unit contained an actual bell which it rang when it received a BEL character. Because the keytop for the O key also showed a left-arrow symbol (from ASCII-1963, which had this character instead of underscore), a noncompliant use of code 15 (control-O, shift in) interpreted as "delete previous character" was also adopted by many early timesharing systems but eventually became neglected.
When a Teletype 33 ASR equipped with the automatic paper tape reader received a control-S (XOFF, an abbreviation for transmit off), it caused the tape reader to stop; receiving control-Q (XON, transmit on) caused the tape reader to resume. This so-called flow control technique became adopted by several early computer operating systems as a "handshaking" signal warning a sender to stop transmission because of impending buffer overflow; it persists to this day in many systems as a manual output control technique. On some systems, control-S retains its meaning, but control-Q is replaced by a second control-S to resume output.
The 33 ASR also could be configured to employ control-R (DC2) and control-T (DC4) to start and stop the tape punch; on some units equipped with this function, the corresponding control character lettering on the keycap above the letter was TAPE and TAPE respectively.[35]
Delete vs backspace
The Teletype could not move its typehead backwards, so it did not have a key on its keyboard to send a BS (backspace). Instead, there was a key marked RUB OUT that sent code 127 (DEL). The purpose of this key was to erase mistakes in a manually-input paper tape: the operator had to push a button on the tape punch to back it up, then type the rubout, which punched all holes and replaced the mistake with a character that was intended to be ignored.[36] Teletypes were commonly used with the less-expensive computers from Digital Equipment Corporation (DEC); these systems had to use what keys were available, and thus the DEL character was assigned to erase the previous character.[37][38] Because of this, DEC video terminals (by default) sent the DEL character for the key marked "Backspace" while the separate key marked "Delete" sent an escape sequence; many other competing terminals sent a BS character for the backspace key.
The early Unix tty drivers, unlike some modern implementations, allowed only one character to be set to erase the previous character in canonical input processing (where a very simple line editor is available); this could be set to BS or DEL, but not both, resulting in recurring situations of ambiguity where users had to decide depending on what terminal they were using (shells that allow line editing, such as ksh, bash, and zsh, understand both). The assumption that no key sent a BS character allowed Ctrl+H to be used for other purposes, such as the "help" prefix command in GNU Emacs.[39]
Escape
Many more of the control characters have been assigned meanings quite different from their original ones. The "escape" character (ESC, code 27), for example, was intended originally to allow sending of other control characters as literals instead of invoking their meaning, an "escape sequence". This is the same meaning of "escape" encountered in URL encodings, C language strings, and other systems where certain characters have a reserved meaning. Over time this interpretation has been co-opted and has eventually been changed.
In modern usage, an ESC sent to the terminal usually indicates the start of a command sequence, which can be used to address the cursor, scroll a region, set/query various terminal properties, and more. They are usually in the form of a so-called "
In contrast, an ESC read from the terminal is most often used as an
End of line
The inherent ambiguity of many control characters, combined with their historical usage, created problems when transferring "plain text" files between systems. The best example of this is the newline problem on various operating systems. Teletype machines required that a line of text be terminated with both "carriage return" (which moves the printhead to the beginning of the line) and "line feed" (which advances the paper one line without moving the printhead). The name "carriage return" comes from the fact that on a manual typewriter the carriage holding the paper moves while the typebars that strike the ribbon remain stationary. The entire carriage had to be pushed (returned) to the right in order to position the paper for the next line.
DEC operating systems (OS/8, RT-11, RSX-11, RSTS, TOPS-10, etc.) used both characters to mark the end of a line so that the console device (originally Teletype machines) would work. By the time so-called "glass TTYs" (later called CRTs or "dumb terminals") came along, the convention was so well established that backward compatibility necessitated continuing to follow it. When Gary Kildall created CP/M, he was inspired by some of the command line interface conventions used in DEC's RT-11 operating system.
Until the introduction of PC DOS in 1981,
Requiring two characters to mark the end of a line introduces unnecessary complexity and ambiguity as to how to interpret each character when encountered by itself. To simplify matters,
Computers attached to the
End of file/stream
The PDP-6 monitor,
The Unix terminal driver uses the end-of-transmission character (EOT), also known as control-D, to indicate the end of a data stream.
In the
Control code chart
Binary |
Oct | Dec | Hex | Abbreviation | Unicode Control Pictures[b] | Caret notation[c] | C escape sequence[d] | Name (1967) | ||
---|---|---|---|---|---|---|---|---|---|---|
1963 | 1965 | 1967 | ||||||||
000 0000 | 000 | 0 | 00 | NULL | NUL | ␀ | ^@ | \0 [e] | Null | |
000 0001 | 001 | 1 | 01 | SOM | SOH | ␁ | ^A | Start of Heading
| ||
000 0010 | 002 | 2 | 02 | EOA | STX | ␂ | ^B | Start of Text
| ||
000 0011 | 003 | 3 | 03 | EOM | ETX | ␃ | ^C | End of Text | ||
000 0100 | 004 | 4 | 04 | EOT | ␄ | ^D | End of Transmission | |||
000 0101 | 005 | 5 | 05 | WRU | ENQ | ␅ | ^E | Enquiry | ||
000 0110 | 006 | 6 | 06 | RU | ACK | ␆ | ^F | Acknowledgement
| ||
000 0111 | 007 | 7 | 07 | BELL | BEL | ␇ | ^G | \a | Bell | |
000 1000 | 010 | 8 | 08 | FE0 | BS | ␈ | ^H | \b | Backspace[f][g] | |
000 1001 | 011 | 9 | 09 | HT/SK | HT | ␉ | ^I | \t | Horizontal Tab[h]
| |
000 1010 | 012 | 10 | 0A | LF | ␊ | ^J | \n | Line Feed
| ||
000 1011 | 013 | 11 | 0B | VTAB | VT | ␋ | ^K | \v | Vertical Tab
| |
000 1100 | 014 | 12 | 0C | FF | ␌ | ^L | \f | Form Feed
| ||
000 1101 | 015 | 13 | 0D | CR | ␍ | ^M | \r | Carriage Return[i]
| ||
000 1110 | 016 | 14 | 0E | SO | ␎ | ^N | Shift Out
| |||
000 1111 | 017 | 15 | 0F | SI | ␏ | ^O | Shift In
| |||
001 0000 | 020 | 16 | 10 | DC0 | DLE | ␐ | ^P | Data Link Escape
| ||
001 0001 | 021 | 17 | 11 | DC1 | ␑ | ^Q | XON )
| |||
001 0010 | 022 | 18 | 12 | DC2 | ␒ | ^R | Device Control 2
| |||
001 0011 | 023 | 19 | 13 | DC3 | ␓ | ^S | XOFF )
| |||
001 0100 | 024 | 20 | 14 | DC4 | ␔ | ^T | Device Control 4
| |||
001 0101 | 025 | 21 | 15 | ERR | NAK | ␕ | ^U | Negative Acknowledgement
| ||
001 0110 | 026 | 22 | 16 | SYNC | SYN | ␖ | ^V | Synchronous Idle
| ||
001 0111 | 027 | 23 | 17 | LEM | ETB | ␗ | ^W | End of Transmission Block | ||
001 1000 | 030 | 24 | 18 | S0 | CAN | ␘ | ^X | Cancel | ||
001 1001 | 031 | 25 | 19 | S1 | EM | ␙ | ^Y | End of Medium
| ||
001 1010 | 032 | 26 | 1A | S2 | SS | SUB | ␚ | ^Z | Substitute | |
001 1011 | 033 | 27 | 1B | S3 | ESC | ␛ | ^[ | \e[j] | Escape[k] | |
001 1100 | 034 | 28 | 1C | S4 | FS | ␜ | ^\ | File Separator
| ||
001 1101 | 035 | 29 | 1D | S5 | GS | ␝ | ^] | Group Separator
| ||
001 1110 | 036 | 30 | 1E | S6 | RS | ␞ | ^^[l] | Record Separator
| ||
001 1111 | 037 | 31 | 1F | S7 | US | ␟ | ^_ | Unit Separator
| ||
111 1111 | 177 | 127 | 7F | DEL | ␡ | ^? | Delete[m][g] |
Other representations might be used by specialist equipment, for example ISO 2047 graphics or hexadecimal numbers.
Printable characters
Codes 20hex to 7Ehex, known as the printable characters, represent letters, digits,
Code 20hex, the "space" character, denotes the space between words, as produced by the space bar of a keyboard. Since the space character is considered an invisible graphic (rather than a control character)[3]: 223 [10] it is listed in the table below instead of in the previous section.
Code 7Fhex corresponds to the non-printable "delete" (DEL) control character and is therefore omitted from this chart; it is covered in the previous section's chart. Earlier versions of ASCII used the up arrow instead of the
Binary |
Oct | Dec | Hex | Glyph | ||
---|---|---|---|---|---|---|
1963 | 1965 | 1967 | ||||
010 0000 | 040 | 32 | 20 | space | ||
010 0001 | 041 | 33 | 21 | ! | ||
010 0010 | 042 | 34 | 22 | " | ||
010 0011 | 043 | 35 | 23 | # | ||
010 0100 | 044 | 36 | 24 | $ | ||
010 0101 | 045 | 37 | 25 | % | ||
010 0110 | 046 | 38 | 26 | & | ||
010 0111 | 047 | 39 | 27 | ' | ||
010 1000 | 050 | 40 | 28 | (
| ||
010 1001 | 051 | 41 | 29 | )
| ||
010 1010 | 052 | 42 | 2A | * | ||
010 1011 | 053 | 43 | 2B | +
| ||
010 1100 | 054 | 44 | 2C | , | ||
010 1101 | 055 | 45 | 2D | - | ||
010 1110 | 056 | 46 | 2E | . | ||
010 1111 | 057 | 47 | 2F | / | ||
011 0000 | 060 | 48 | 30 | 0
| ||
011 0001 | 061 | 49 | 31 | 1
| ||
011 0010 | 062 | 50 | 32 | 2
| ||
011 0011 | 063 | 51 | 33 | 3
| ||
011 0100 | 064 | 52 | 34 | 4
| ||
011 0101 | 065 | 53 | 35 | 5
| ||
011 0110 | 066 | 54 | 36 | 6
| ||
011 0111 | 067 | 55 | 37 | 7
| ||
011 1000 | 070 | 56 | 38 | 8
| ||
011 1001 | 071 | 57 | 39 | 9
| ||
011 1010 | 072 | 58 | 3A | : | ||
011 1011 | 073 | 59 | 3B | ; | ||
011 1100 | 074 | 60 | 3C | < | ||
011 1101 | 075 | 61 | 3D | = | ||
011 1110 | 076 | 62 | 3E | > | ||
011 1111 | 077 | 63 | 3F | ? | ||
100 0000 | 100 | 64 | 40 | @ | ` |
@ |
100 0001 | 101 | 65 | 41 | A | ||
100 0010 | 102 | 66 | 42 | B | ||
100 0011 | 103 | 67 | 43 | C | ||
100 0100 | 104 | 68 | 44 | D | ||
100 0101 | 105 | 69 | 45 | E | ||
100 0110 | 106 | 70 | 46 | F | ||
100 0111 | 107 | 71 | 47 | G | ||
100 1000 | 110 | 72 | 48 | H | ||
100 1001 | 111 | 73 | 49 | I | ||
100 1010 | 112 | 74 | 4A | J | ||
100 1011 | 113 | 75 | 4B | K | ||
100 1100 | 114 | 76 | 4C | L | ||
100 1101 | 115 | 77 | 4D | M | ||
100 1110 | 116 | 78 | 4E | N | ||
100 1111 | 117 | 79 | 4F | O | ||
101 0000 | 120 | 80 | 50 | P | ||
101 0001 | 121 | 81 | 51 | Q | ||
101 0010 | 122 | 82 | 52 | R | ||
101 0011 | 123 | 83 | 53 | S | ||
101 0100 | 124 | 84 | 54 | T | ||
101 0101 | 125 | 85 | 55 | U | ||
101 0110 | 126 | 86 | 56 | V | ||
101 0111 | 127 | 87 | 57 | W | ||
101 1000 | 130 | 88 | 58 | X | ||
101 1001 | 131 | 89 | 59 | Y | ||
101 1010 | 132 | 90 | 5A | Z | ||
101 1011 | 133 | 91 | 5B | [
| ||
101 1100 | 134 | 92 | 5C | \ | ~ | \ |
101 1101 | 135 | 93 | 5D | ]
| ||
101 1110 | 136 | 94 | 5E | ↑ |
^
| |
101 1111 | 137 | 95 | 5F | ← |
_ | |
110 0000 | 140 | 96 | 60 | @ | `
| |
110 0001 | 141 | 97 | 61 | a | ||
110 0010 | 142 | 98 | 62 | b | ||
110 0011 | 143 | 99 | 63 | c | ||
110 0100 | 144 | 100 | 64 | d | ||
110 0101 | 145 | 101 | 65 | e | ||
110 0110 | 146 | 102 | 66 | f | ||
110 0111 | 147 | 103 | 67 | g | ||
110 1000 | 150 | 104 | 68 | h | ||
110 1001 | 151 | 105 | 69 | i | ||
110 1010 | 152 | 106 | 6A | j | ||
110 1011 | 153 | 107 | 6B | k | ||
110 1100 | 154 | 108 | 6C | l | ||
110 1101 | 155 | 109 | 6D | m | ||
110 1110 | 156 | 110 | 6E | n | ||
110 1111 | 157 | 111 | 6F | o | ||
111 0000 | 160 | 112 | 70 | p | ||
111 0001 | 161 | 113 | 71 | q | ||
111 0010 | 162 | 114 | 72 | r | ||
111 0011 | 163 | 115 | 73 | s | ||
111 0100 | 164 | 116 | 74 | t | ||
111 0101 | 165 | 117 | 75 | u | ||
111 0110 | 166 | 118 | 76 | v | ||
111 0111 | 167 | 119 | 77 | w | ||
111 1000 | 170 | 120 | 78 | x | ||
111 1001 | 171 | 121 | 79 | y | ||
111 1010 | 172 | 122 | 7A | z | ||
111 1011 | 173 | 123 | 7B | {
| ||
111 1100 | 174 | 124 | 7C | ACK |
¬ |
| |
111 1101 | 175 | 125 | 7D | }
| ||
111 1110 | 176 | 126 | 7E | ESC | | | ~ |
Usage
ASCII was first used commercially during 1963 as a seven-bit teleprinter code for
On March 11, 1968, US President
I have also approved recommendations of the
Secretary of Commerce [Luther H. Hodges] regarding standards for recording the Standard Code for Information Interchange on magnetic tapes and paper tapes when they are used in computer operations. All computers and related equipment configurations brought into the Federal Government inventory on and after July 1, 1969, must have the capability to use the Standard Code for Information Interchange and the formats prescribed by the magnetic tape and paper tape standards when these media are used.
ASCII was the most common character encoding on the
Variants and derivations
As computer technology spread throughout the world, different
7-bit codes
From early in its development,[58] ASCII was intended to be just one of several national variants of an international character code standard.
Other international standards bodies have ratified character encodings such as
Many other countries developed variants of ASCII to include non-English letters (e.g.
It would share most characters in common, but assign other locally useful characters to several code points reserved for "national use". However, the four years that elapsed between the publication of ASCII-1963 and ISO's first acceptance of an international recommendation during 1967[59] caused ASCII's choices for the national use characters to seem to be de facto standards for the world, causing confusion and incompatibility once other countries did begin to make their own assignments to these code points.
ISO/IEC 646, like ASCII, is a 7-bit character set. It does not make any additional codes available, so the same code points encoded different characters in different countries. Escape codes were defined to indicate which national variant applied to a piece of text, but they were rarely used, so it was often impossible to know what variant to work with and, therefore, which character a code represented, and in general, text-processing systems could cope with only one variant anyway.
Because the bracket and brace characters of ASCII were assigned to "national use" code points that were used for accented letters in other national variants of ISO/IEC 646, a German, French, or Swedish, etc. programmer using their national variant of ISO/IEC 646, rather than ASCII, had to write, and thus read, something such as
ä aÄiÜ = 'Ön'; ü
instead of
{ a[i] = '\n'; }
In Japan and Korea, still as of the 2020s,[update] a variation of ASCII is used, in which the
In Europe, teletext character sets, which are variants of ASCII, are used for broadcast TV subtitles, defined by World System Teletext and broadcast using the DVB-TXT standard for embedding teletext into DVB transmissions.[60] In the case that the subtitles were initially authored for teletext and converted, the derived subtitle formats are constrained to the same character sets.
8-bit codes
Eventually, as 8-, 16-, and 32-bit (and later 64-bit) computers began to replace 12-, 18-, and 36-bit computers as the norm, it became common to use an 8-bit byte to store each character in memory, providing an opportunity for extended, 8-bit relatives of ASCII. In most cases these developed as true extensions of ASCII, leaving the original character-mapping intact, but adding additional character definitions after the first 128 (i.e., 7-bit) characters.
For some countries, 8-bit extensions of ASCII were developed that included support for characters used in local languages; for example,
Even for markets where it was not necessary to add many characters to support additional languages, manufacturers of early home computer systems often developed their own 8-bit extensions of ASCII to include additional characters, such as
.Most ASCII extensions are based on ASCII-1967 (the current standard), but some extensions are instead based on the earlier ASCII-1963. For example, PETSCII, which was developed by Commodore International for their 8-bit systems, is based on ASCII-1963. Likewise, many Sharp MZ character sets are based on ASCII-1963.
IBM defined
The
Unicode
ASCII was incorporated into the Unicode (1991) character set as the first 128 symbols, so the 7-bit ASCII characters have the same numeric codes in both sets. This allows UTF-8 to be backward compatible with 7-bit ASCII, as a UTF-8 file containing only ASCII characters is identical to an ASCII file containing the same sequence of characters. Even more importantly, forward compatibility is ensured as software that recognizes only 7-bit ASCII characters as special and does not alter bytes with the highest bit set (as is often done to support 8-bit ASCII extensions such as ISO-8859-1) will preserve UTF-8 data unchanged.[63]
See also
- 3568 ASCII – an asteroid named after the character encoding
- Alt codes– Method for entering characters into a computer
- ASCII 8– ASCII code 08, "BS" or Backspace
- ASCII art – Computer art form using text characters
- ASCII Ribbon Campaign– Campaign for plain text (only) emails
- Basic Latin (Unicode block) – ASCII as a subset of Unicode
- Extended ASCII – Nickname for 8-bit ASCII-derived character sets
- HTML decimal character rendering
- Jargon File – a glossary of computer programmer slang which includes a list of common slang names for ASCII characters
- List of computer character sets
- List of Unicode characters
Notes
- ^ most-significant bits.[15]Depending on the horizontal or vertical representation of the character map, sticks can correspond with either table rows or columns.
- ^ The Unicode characters from the "Control Pictures" area U+2400 to U+2421 reserved for representing control characters when it is necessary to print or display them rather than have them perform their intended function. Some browsers may not display these properly.
- ^ Caret notation is often used to represent control characters on a terminal. On most text terminals, holding down the Ctrl key while typing the second character will type the control character. Sometimes the shift key is not needed, for instance
^@
may be typable with just Ctrl+2 or Ctrl+Space. - ^ Character escape sequences in C programming language and many other languages influenced by it, such as Java and Perl (though not all implementations necessarily support all escape sequences).
- ^ Entering any Single-Byte character is supported by escaping its octal value. However, because of the role of NULL in C-strings, this case see particular use.
- ^ The Backspace character can also be entered by pressing the ← Backspace key on some systems.
- ^ a b The ambiguity of Backspace is due to early terminals designed assuming the main use of the keyboard would be to manually punch paper tape while not connected to a computer. To delete the previous character, one had to back up the paper tape punch, which for mechanical and simplicity reasons was a button on the punch itself and not the keyboard, then type the rubout character. They therefore placed a key producing rubout at the location used on typewriters for backspace. When systems used these terminals and provided command-line editing, they had to use the "rubout" code to perform a backspace, and often did not interpret the backspace character (they might echo "^H" for backspace). Other terminals not designed for paper tape made the key at this location produce Backspace, and systems designed for these used that character to back up. Since the delete code often produced a backspace effect, this also forced terminal manufacturers to make any Delete key produce something other than the Delete character.
- Tab charactercan also be entered by pressing the Tab ↹ key on most systems.
- Carriage Returncharacter can also be entered by pressing the ↵ Enter or Return key on most systems.
- GCC.
- ^ The Escape character can also be entered by pressing the Esc key on some systems.
- caretkeys).
- ^ The Delete character can sometimes be entered by pressing the ← Backspace key on some systems.
- ^ Printed out, the characters are:
!"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~
References
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In addition, it defines codes for 33 nonprinting, mostly obsolete control characters that affect how the text is processed.
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The transmitted code use International Telegraph Alphabet No. 2 (ITA-2) which was introduced by CCITT in 1924.
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Using a "new-line" function (combined carriage-return and line-feed) is simpler for both man and machine than requiring both functions for starting a new line; the American National Standard X3.4-1968 permits the line-feed code to carry the new-line meaning.
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There was the change from 1961 ASCII to 1968 ASCII. Some computer languages used characters in 1961 ASCII such as up arrow and left arrow. These characters disappeared from 1968 ASCII. We worked with Fred Mocking, who by now was in Sales at Teletype, on a type cylinder that would compromise the changing characters so that the meanings of 1961 ASCII were not totally lost. The underscore character was made rather wedge-shaped so it could also serve as a left arrow.
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Further reading
- S2CID 9591147.
- Bemer, Robert William (2003-05-23). "The Babel of Codes Prior to ASCII: The 1960 Survey of Coded Character Sets: The Reasons for ASCII". Archived from the originalon 2013-10-17. Retrieved 2016-05-09, from:
- S2CID 21403172.
- Smith, H. J.; Williams, F. A. (December 1960). "Survey of punched card codes". .
- "American National Standard Code for Information Interchange | ANSI X3.4-1977" (PDF). National Institute for Standards. 1977. Archived (PDF) from the original on 2022-10-09. (facsimile, not machine readable)
- Robinson, G. S.; Cargill, C. (1996). "History and impact of computer standards". doi:10.1109/2.539725.
- Mullendore, Ralph Elvin (1964) [1963]. Ptak, John F. (ed.). "On the Early Development of ASCII – The History of ASCII". JF Ptak Science Books (published March 2012). Archived from the original on 2016-05-26. Retrieved 2016-05-26.
External links
- "C0 Controls and Basic Latin – Range: 0000–007F" (PDF). The Unicode Standard 8.0. Unicode, Inc. 2015 [1991]. Archived(PDF) from the original on 2016-05-26. Retrieved 2016-05-26.