ASCII |
ASCII ( American Standard Code for Information Interchange ), generally IPA for English , (ASK-ee) is a character set and a character encoding based on the Latin alphabet as used in modern English language (see English alphabet). ASCII codes represent character (computing) in computers, in other telecommunications equipment, and in control devices that work with text. Most recent character encoding has an ASCII-like base.
ASCII defines the following printable characters, presented here in numerical order of their ASCII value:
! #$%& ()*+,-./ 0123456789:; @ABCDEFGHIJKLMNO PQRSTUVWXYZ[]^_ `abcdefghijklmno pqrstuvwxyz
# Printable Representation, the Unicode glyphs reserved for representing control characters when it is necessary to print or display them rather than have them perform their intended function. # Control key Sequence, the traditional key sequences for inputting control characters. The caret (^) represents the Control or Ctrl key that must be held down while pressing the second key in the sequence. The caret-key representation is also used by some software to represent control characters. # The Backspace character can also be entered by pressing the Backspace , Bksp , or ← key on some systems. # The Delete character can also be entered by pressing the Delete or Del key. It can also be entered by pressing the Backspace , Bksp , or ← key on some systems. # The Escape character can also be entered by pressing the Escape or Esc key on some systems. # The Carriage Return character can also be entered by pressing the Return , Ret , Enter , or ↵ key on most systems. # The ambiguity surrounding the Backspace key comes from systems that translated the DEL control character into a BS (backspace) before transmitting it. Some software was unable to process the character and would display ^H instead. ^H persists in messages today as a deliberate humorous device, e.g. there is a sucker born every minute. A less common variant of this involves the use of ^W , which in some text editors means delete previous word . The example sentence would therefore also work as there s a sucker^W potential customer born every minute .
=ASCII printable characters=
Code 32, the Space (punctuation), denotes the space between words, as produced by the large space-bar of a keyboard. Codes 33 to 126, known as the printable characters, represent letters, digits, punctuation marks, and a few miscellaneous symbols.
Seven-bit ASCII provided seven national characters and, if the combined hardware and software permit, can use overstrikes to simulate some additional international characters: in such a scenario a backspace can precede a grave accent (which the American and British standards, but only those standards, also call opening single quotation mark ), a tilde, or a breath mark (inverted vel).
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| | ]] |- |0111 1110 |126 |7E |Tilde |} |}
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 US-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 Extended ASCII , 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 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 8859-1 and original 7-bit ASCII remain the most common character encodings in use today.
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 Character string (computer science).
=See also=
==Related topics==
*ASCII art *ASCII games *Binary and text files *EBCDIC *Extended ASCII *ISCII *ISO 646 *ISO 8859 *Unicode *UTF-8 *VISCII
==Computer (family)-specific ASCII variants==
*ATASCII *PETSCII *ZX Spectrum character set
==ASCII in space==
*3568 ASCII
=External links=
=Notes and references=
# International Organization for Standardization (December 1, 1975). [http://www.itscj.ipsj.or.jp/ISO-IR/001.pdf The set of control characters for ISO 646] . Internet Assigned Numbers Authority Registry . Alternate USA version: [http://www.itscj.ipsj.or.jp/ISO-IR/006.pdf]. Accessed August 7, 2005. # Internet Assigned Numbers Authority (January 28, 2005). [http://www.iana.org/assignments/character-sets Character Sets] . Accessed August 7, 2005.|
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