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ASCII (Themerican Standard Code for I personallynformation Wenterchange), usually pronounced , (ASK-ee) is a character set and a character encoding based on the Roman alphabet as used within modern English (see English alphabet). ASCII codes represent text in computers, in more communications equipment, and inside control gear that operate by having text. Virtually all typically, today, character encryption has an ASCII-prefer base. ASCII defines a below printable characters, bestowed on this text around numerical sequentially of their ASCII value:
!"#$%&'()*+,-./ 0123456789:;<=>? @ABCDEFGHIJKLMNO PQRSTUVWXYZ[\]^_ `abcdefghijklmno pqrstuvwxyz~
Overview Like other character representation computer codes, ASCII specifies a correspondence between digital bit patterns and the symbols/glyphs of a written language, thus allowing digital devices to communicate with each other and to process, store, and communicate character-oriented information. The ASCII character encoding ASCII is, strictly, a seven-bit code, meaning that it uses the bit patterns representable with seven binary digits (a range of 0 to 127 decimal) to represent character information. At the time ASCII was introduced, many computers dealt with eight-bit groups (bytes or, more specifically, octets) as the smallest unit of information; the eighth bit was commonly used as a parity bit for error checking on communication lines or other device-specific functions. Machines which did not use parity typically set the eighth bit to zero, though some systems such as Prime machines running PRIMOS set the eighth bit of ASCII characters to one. ASCII does not specify any way to include information about the conceptual structure or appearance of a piece of text. That requires other standards, such as those specifying markup languages. Conceptual structure can be included using XML and appearance can be specified by using HTML for relatively simple things, SGML for more complex things, or PostScript, Display PostScript, TeX, or XSL-FO for advanced layout and font control.
History Historically, ASCII developed from telegraphic codes and first entered commercial use as a 7-bit teleprinter code promoted by Bell data services. The Bell System had previously planned to use a 6-bit code (derived from Fieldata) that added punctuation and lower-case letters to the earlier 5-bit Baudot teleprinter-code, but became persuaded instead to join the ASA subcommittee that had started to develop ASCII. Baudot helped in the automation of sending and receiving of telegraphic messages, and took many features from Morse code; however, unlike Morse code, Baudot used constant-length codes. Compared to earlier telegraph codes, the proposed Bell code and ASCII both underwent re-ordering for more convenient sorting (especially alphabetization) of lists, and added features for devices other than teleprinters. Bob Bemer introduced features such as the 'escape sequence'. The American Standards Association (ASA, later to become ANSI) first published ASCII as a standard in 1963. ASCII-1963 lacked the lowercase letters, and had an up-arrow (↑) instead of the caret (^) and a left-arrow (←) instead of the underscore (_). The 1967 version added the lowercase letters, changed the names of a few control characters and moved the two controls ACK and ESC from the lowercase letters area into the control codes area. Many variations of ASCII exist, but its present, most widely-used form uses the ANSI X3.4-1986 definition, also standardized as ECMA-6, ISO/IEC 646:1991 International Reference Version, ITU-T Recommendation T.50 (09/92), and Request for Comments RFC 20. ASCII has become embedded in its probable replacement, Unicode, as the 'lowest' 128 characters. Some observers consider ASCII the most "successful" software standard ever promulgated.
ASCII control characters ASCII reserves the first 32 codes (numbers 0–31 decimal) for control characters: codes originally intended not to carry character information, but rather to control devices (such as printers) that make use of ASCII. For example, character 10 represents the "line feed" function (which causes a printer to advance its paper), and character 27 represents the "escape" key often found in the top left corner of common keyboards. Code 127 (all seven bits on), another special character, equates to "delete" or "rubout". Though its function resembles that of other control characters, the designers of ASCII used this pattern so that it could "erase" a section of paper tape (a popular storage medium until the 1980s) by punching all possible holes at a particular character position, thus effectively replacing any previous information. Many of the ASCII control codes serve (or served) to mark data packets, or to control a data transmission protocol (e.g. ENQuiry [effectively, "any stations out there?"], ACKnowledge, Negative AcKnowledge, Start Of Header, Start Of Text, End Of Text, etc). ESCape and SUBstitute permit a communications protocol to, for instance, mark binary data so that if it contains codes with the same pattern as a protocol character, the recipient will process the code as data. The designers of ASCII intended the separator characters ("Record Separator", etc.) for use with magnetic tape systems. Two of the device control characters, commonly interpreted as XON and XOFF, generally function as flow control characters to throttle data flow to a slow device (such as a printer) from a fast device (such as a computer) - so data does not overrun and get lost. Early users of ASCII adopted some of the control codes to represent "meta trading tools" such as end-of-line, start/end of a data element, and so on. These assignments often conflict, so part of the effort in converting data from one format to another involves making the correct meta information transformations. For example, the character(s) representing end-of-line ("newline") in text data files/streams vary from operating system to operating system. When moving files from one system to another, the conversion process must recognize these characters as end-of-line markers and handle them appropriately. Today, ASCII users use the control characters less and less—with the exception of carriage return" and/or "line feed". Modern markup languages, modern communication protocols, a move from either text-depending to graphic gear, & the death of telex, punch-cards, & paper tapes keep close at hand rendered virtually all of the ascii control character obsolete.
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!style="width: 5.5em"|Binary
!style="width: 2.5em"|Oct
!style="width: 2.5em"|Dec
!style="width: 2.5em"|Hex
!style="width: 2.5em"|Abbr
!style="width: 2.5em"|PR!style="width: 2.5em"|CS!Description
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|0000 0000
|000
|0
|00
|NUL
|␀
|^@
|style="text-align: left; margin-left: 0.2em"|Null character
|-
|0000 0001
|001
|1
|01
|SOH
|␁
|^A
|style="text-align: left; margin-left: 0.2em"|Start of Header
|-
|0000 0010
|002
|2
|02
|STX
|␂
|^B
|style="text-align: left; margin-left: 0.2em"|Start of Text
|-
|0000 0011
|003
|3
|03
|ETX
|␃
|^C
|style="text-align: left; margin-left: 0.2em"|End of Text
|-
|0000 0100
|004
|4
|04
|EOT
|␄
|^D
|style="text-align: left; margin-left: 0.2em"|End of Transmission
|-
|0000 0101
|005
|5
|05
|ENQ
|␅
|^E
|style="text-align: left; margin-left: 0.2em"|Enquiry
|-
|0000 0110
|006
|6
|06
|ACK
|␆
|^F
|style="text-align: left; margin-left: 0.2em"|Acknowledgement
|-
|0000 0111
|007
|7
|07
|BEL
|␇
|^G
|style="text-align: left; margin-left: 0.2em"|Bell
|-
|0000 1000
|010
|8
|08
|BS
|␈
|^H
|style="text-align: left; margin-left: 0.2em"|Backspace|-
|0000 1001
|011
|9
|09
|HT
|␉
|^I
|style="text-align: left; margin-left: 0.2em"|Horizontal Tab
|-
|0000 1010
|012
|10
|0A
|LF
|␊
|^J
|style="text-align: left; margin-left: 0.2em"|Line feed
|-
|0000 1011
|013
|11
|0B
|VT
|␋
|^K
|style="text-align: left; margin-left: 0.2em"|Vertical Tab
|-
|0000 1100
|014
|12
|0C
|FF
|␌
|^L
|style="text-align: left; margin-left: 0.2em"|Form feed
|-
|0000 1101
|015
|13
|0D
|CR
|␍
|^M
|style="text-align: left; margin-left: 0.2em"|Carriage return|-
|0000 1110
|016
|14
|0E
|SO
|␎
|^N
|style="text-align: left; margin-left: 0.2em"|Shift Out
|-
|0000 1111
|017
|15
|0F
|SI
|␏
|^O
|style="text-align: left; margin-left: 0.2em"|Shift In
|-
|0001 0000
|020
|16
|10
|DLE
|␐
|^P
|style="text-align: left; margin-left: 0.2em"|Data Hyperlink Escape
|-
|0001 0001
|021
|17
|11
|DC1
|␑
|^Q
|style="text-align: left; margin-left: 0.2em"|Device Control One (frequently. XON)
|-
|0001 0010
|022
|18
|12
|DC2
|␒
|^R
|style="text-align: left; margin-left: 0.2em"|Device Control 2
|-
|0001 0011
|023
|19
|13
|DC3
|␓
|^S
|style="text-align: left; margin-left: 0.2em"|Device Control Three (often. XOFF)
|-
|0001 0100
|024
|20
|14
|DC4
|␔
|^T
|style="text-align: left; margin-left: 0.2em"|Device Control 4
|-
|0001 0101
|025
|21
|15
|NAK
|␕
|^U
|style="text-align: left; margin-left: 0.2em"|Negative Acknowledgement
|-
|0001 0110
|026
|22
|16
|SYN
|␖
|^V
|style="text-align: left; margin-left: 0.2em"|Synchronous Idle
|-
|0001 0111
|027
|23
|17
|ETB
|␗
|^W
|style="text-align: left; margin-left: 0.2em"|End of Trans. Block
|-
|0001 1000
|030
|24
|18
|CAN
|␘
|^X
|style="text-align: left; margin-left: 0.2em"|Cancel
|-
|0001 1001
|031
|25
|19
|EM
|␙
|^Y
|style="text-align: left; margin-left: 0.2em"|End of Medium
|-
|0001 1010
|032
|26
|1A
|SUB
|␚
|^Z
|style="text-align: left; margin-left: 0.2em"|Substitute
|-
|0001 1011
|033
|27
|1B
|ESC
|␛
|^
ASCII printable characters Code 32, a "space" character, denotes the space between words, as produced by the large space-bar of a keyboard. Codes 33 to 126, referred to as a printable characters, represent letters, digits, punctuation marks, & two or three miscellaneous symbols. 7-bit ASCII provided seven "national" characters &, around case the conjunct devices & software program permit, could utilise overstrikes to simulate occasionally extrthe international characters: in such the scenario a backspace key may precede a grave accent (which the U.s. & British standards, but only people standards, as well call for "opening single quotation mark"), the tilde, or the breath mark (anatropous vel).
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|- valign="bottom"
!style="breadth: Quintuplet.5em"|Bin
!style="breadth: Deuce.5em"|Dec
!style="breadth: Ii.5em"|Hex
!Glyph
|-
|0100 0000
|64
|40
|@
|-
|0100 0001
|65
|41
|A
|-
|0100 0010
|66
|42
|B
|-
|0100 0011
|67
|43
|C
|-
|0100 0100
|68
|44
|D
|-
|0100 0101
|69
|45
|E
|-
|0100 0110
|70
|46
|F
|-
|0100 0111
|71
|47
|G
|-
|0100 1000
|72
|48
|H
|-
|0100 1001
|73
|49
|I
|-
|0100 1010
|74
|4A
|J
|-
|0100 1011
|75
|4B
|K
|-
|0100 1100
|76
|4C
|L
|-
|0100 1101
|77
|4D
|M
|-
|0100 1110
|78
|4E
|N
|-
|0100 1111
|79
|4F
|O
|-
|0101 0000
|80
|50
|P
|-
|0101 0001
|81
|51
|Q
|-
|0101 0010
|82
|52
|R
|-
|0101 0011
|83
|53
|S
|-
|0101 0100
|84
|54
|T
|-
|0101 0101
|85
|55
|U
|-
|0101 0110
|86
|56
|V
|-
|0101 0111
|87
|57
|W
|-
|0101 1000
|88
|58
|X
|-
|0101 1001
|89
|59
|Y
|-
|0101 1010
|90
|5A
|Z
|-
|0101 1011
|91
|5B
| Processors can convert uppercase characters to lowercase by adding 32 to their ASCII value; in binary, devices can accomplish this simply by setting the sixth-least significant bit to 1.
Aliases for ASCII RFC 1345 (published in June 1992) and the [http://www.iana.org/assignments/character-sets IANA registry of character sets] (ongoing), both recognize the following case-insensitive aliases for ASCII as suitable for use on the Internet:
Of these, only the aliases "America-ASCII" and "ASCII" have achieved widespread use. One often finds them in the optional "charset" parameter in the Content-Type header of some MIME messages, in the equivalent "meta" element of some HTML documents, and in the encoding declaration part of the prolog of some XML documents.
Variants of ASCII
As computer technology spread throughout the world, different standards bodies and corporations developed many variations of ASCII in order to facilitate the expression of non-English languages that used Roman-based alphabets. One could class some of these variations as "ASCII extensions", although some mis-apply that term to cover all variants, including those that do not preserve ASCII's character-map in the 7-bit range.
ISO 646 (1972), the first attempt to remedy the pro-English-language bias, created compatibility problems, since it remained a 7-bit character-set. It made no additional codes available, so it reassigned some in language-specific variants. It thus became impossible to know what character a code represented without knowing which variant to work with, and text-processing systems could generally cope with only one variant anyway.
Eventually, improved technology brought out-of-band means to represent the information formerly encoded in the eighth bit of each byte, freeing this bit to add another 128 additional character-codes for new assignments. For example, IBM developed 8-bit code pages, such as code page 437, which replaced the control-characters with graphic symbols such as smiley faces, and mapped additional graphic characters to the upper 128 bytes. Operating systems such as DOS supported these code-pages, and manufacturers of IBM PCs supported them in hardware.
Eight-bit standards such as ISO/IEC 8859 and MacRoman developed as true extensions of ASCII, leaving the original character-mapping intact and just adding additional values above the 7-bit range. This enabled the representation of a broader range of languages, but these standards continued to suffer from incompatibilities and limitations. Still, ISO/IEC 8859-1 and original 7-bit ASCII remain the most common character encodings in use today.
Unicode and the ISO/IEC 10646 Universal Character Set (UCS) have a much wider array of characters, and their various encoding forms have begun to supplant ISO/IEC 8859 and ASCII rapidly in many environments. While ASCII basically uses 7-bit codes, Unicode and the UCS use relatively abstract "code points": non-negative integer numbers that map, using different encoding forms and schemes, to sequences of one or more 8-bit bytes. To permit backward compatibility, Unicode and the UCS assign the first 128 code points to the same characters as ASCII. One can therefore think of ASCII as a 7-bit encoding scheme for a very small subset of Unicode and of the UCS. The popular UTF-8 encoding-form prescribes the use of one to four 8-bit code values for each code point character, and equates exactly to ASCII for the code values below 128. Other encoding forms such as UTF-16 resemble ASCII in how they represent the first 128 characters of Unicode, but tend to use 16 or 32 bits per character, so they require conversion for compatibility.
The portmanteau word ASCIIbetical has evolved to describe the collation of data in ASCII-code order rather than "standard" alphabetical order (which requires some tricky computation, and varies with language).
ASCII contains many characters not in common use (or at least not commonly spoken of) outside of the computing context; the "popularization" of these characters encouraged users to agree on standard names for them. See the pronunciation guide in the external links, below.
The abbreviation ASCIIZ or ASCIZ refers to a null-terminated ASCII string.
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Jim's ASCII Chart Page ASCII tables, ASCII charts, in a variety of forms. Also hex-to-decimal and hex-to-ASCII conversions, and other references. www.Asciitable.com ASCII table with hexadecimal and octal conversions, includes the 32 non printing characters with descriptions, and the IBM extended codes. |
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