XML: Key Traps
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ASCII codes represent text in computers, telecommunications equipment, and other devices. Most modern character-encoding schemes are based on ASCII, although they support many additional characters. Its first commercial use was as a seven-bit teleprinter code promoted by Bell data services. The first edition of the standard was published in  underwent a major revision during  and experienced its most recent update during For example, lowercase j would become binary and decimal ASCII includes definitions for characters: The X3 committee made other changes, including other new characters the brace and vertical bar characters renaming some control characters SOM became start of header SOH and moving or removing others RU was removed.
They proposed a 9-track standard for magnetic tape, and attempted to deal with some punched card formats. Like other character encodings, ASCII specifies a correspondence between digital bit patterns and character symbols i. This allows digital devices to communicate with each other and to process, store, and communicate character-oriented information such as written language.
Before ASCII was developed, the encodings in use included 26 alphabeticcharacters, 10 numerical digits, and from 11 to 25 special graphic symbols. The committee debated the possibility of a shift function like in ITA2which would allow more than 64 codes to be represented by a six-bit code. In a shifted code, some character codes determine choices between options for the following character codes.
It allows compact encoding, but is less reliable for data transmission, as an error in transmitting the shift code typically makes a long part of the transmission unreadable. The committee considered an eight-bit code, since eight bits octets would allow two four-bit patterns to efficiently encode two digits with binary-coded decimal. However, it would require all data transmission to send eight bits when seven could suffice. The committee voted to use a seven-bit code to minimize costs associated with data transmission.
Since perforated tape at the time could record eight bits in one position, it also allowed for a parity bit for error checking if desired. The code itself was patterned so that most control codes were together and all graphic codes were together, for ease of identification.
The committee decided it was important to support arrow ascii table binary and decimal for z character alphabets, and chose to pattern ASCII so it could be reduced easily to a usable character set of graphic codes, : Lowercase letters were therefore not interleaved with uppercase. To keep options available for lowercase letters and other graphics, the special and numeric codes were arranged before arrow ascii table binary and decimal for z letters, and the letter A was placed in position 41 hex to match the draft of the corresponding British standard.
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.
This discrepancy from typewriters led to bit-paired keyboards, notably the Teletype Model 33, which used the left-shifted arrow ascii table binary and decimal for z corresponding to ASCII, not to traditional mechanical typewriters. These were positioned to maximize the Hamming distance between their bit patterns.
ASCII reserves the first 32 codes numbers 0—31 decimal for control characters: RFC refers to control characters that do not include carriage return, line feed orwhite space as non-whitespace control characters.
Other schemes, such as markup languages, address page and document layout and formatting. Paper tape was a very popular medium for long-term program storage until the s, less costly and in some ways less fragile than magnetic tape. The Model 33 was also notable for taking the description of Control-G BEL, meaning audibly alert the operator literally, as the unit contained an actual bell which it rang when it received a BEL character.
Since the original standard did not give detailed interpretation for most control codes, interpretations of this code varied. The original Teletype meaning, and the intent of the arrow ascii table binary and decimal for z, was to make it an ignored character, the same as NUL all zeroes. This was useful specifically for paper tape, because punching the all-ones bit pattern on top of an existing mark would obliterate it. Many more of the control codes have been given meanings quite different from their original ones.
Over time this meaning has been co-opted and has eventually been changed. Arrow ascii table binary and decimal for z ESC sent from the terminal is most often used as an out-of-band character used to terminate an operation, as in the TECO and vi text editors. In graphical user interface GUI and windowing systems, ESC generally causes an application to abort its current operation or to exit terminate altogether. The best example of this is the newline problem on various operating systems.
The entire carriage had to be pushed returned to the right in order to position the left margin of the paper for the next line. Unfortunately, requiring two characters to mark arrow ascii table binary and decimal for z end of a line introduces unnecessary complexity and questions as to how to interpret each character when encountered alone. To simplify matters plain text data streams, including files, on Multics  used line feed LF alone as a line terminator.
Unix and Unix-like systems, and Amiga systems, adopted this convention from Multics. The end-of-text code ETXalso known as Control-C, was inappropriate for a variety of reasons, while using Z as the control code to end a file is analogous to it ending the alphabet and serves as a very convenient mnemonic aid. A historically common and still prevalent convention uses the ETX code convention to interrupt and halt a program via an input data stream, usually from a keyboard.
Other representations might be used by specialist equipment, for example ISO graphics or hexadecimal numbers. Codes 20 hex to 7E hexknown as the printable characters, represent letters, digits, punctuation marks, and a few miscellaneous symbols. There are 95 printable characters in total. Since the space character is considered an invisible graphic rather than a control character : Bob Bemer introduced features such as the escape sequence.
On March 11,U. I have also approved recommendations of the Secretary of Commerce 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,must have the capability to use the Standard Code for Information Interchange and the formats prescribed by the magnetic tape and paper tape standards arrow ascii table binary and decimal for z these media are used. As computer technology spread throughout the world, different standards bodies and corporations developed many variations of ASCII to facilitate the expression of non-English languages that used Roman-based alphabets.
From early in its development,  ASCII was intended to be just one of several national variants of an international character code standard. For example, Canada had its own version that supported French characters. 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.
C trigraphs were created to solve this problem for ANSI C, although their late introduction and inconsistent implementation in compilers limited their use. Eventually, as 8- and bit and later bit computers began to replace and 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 arrow ascii table binary and decimal for z character definitions after the first i.
Most early home computer systems developed their own 8-bit character sets containing line-drawing and game glyphs, and often filled arrow ascii table binary and decimal for z some or all of the control characters from 0 to 31 arrow ascii table binary and decimal for z more graphics.
The IBM PC defined code pagewhich replaced the control characters with graphic symbols such as smiley faces, and mapped additional graphic characters to the upper positions.
The Macintosh defined Mac OS Roman and Postscript also defined a set, both of these contained both international letters and typographic punctuation marks instead of graphics, more like modern character sets.
A popular further extension designed by Microsoft,Windows often mislabeled as ISOadded the typographic punctuation marks needed for traditional text printing. This article is about the character encoding.