Overview and History of ASCII
– ASCII was developed from telegraph code.
– Its first commercial use was in the Teletype Model 33 and Model 35.
– Work on the ASCII standard began in May 1961.
– The first edition of the standard was published in 1963.
– ASCII underwent a major revision in 1967 and its most recent update in 1986.
– ASCII was developed by the American Standards Association (ASA) and later adopted by the American National Standards Institute (ANSI).
– ASCII was published as ASA X3.4-1963.
– It went through several revisions, including USAS X3.4-1967 and ANSI X3.4-1986.
– The X3 committee made changes to ASCII, including adding new characters and renaming control characters.
Design Considerations of ASCII
– ASCII was based on earlier teleprinter encoding systems.
– It specified a correspondence between digital bit patterns and character symbols.
– Before ASCII, encodings included alphabetic characters, numerical digits, and special graphic symbols.
– ASCII required at least a seven-bit code.
– The committee considered using an eight-bit code but decided on seven bits to minimize costs.
– The code was patterned so that control codes were grouped together and graphic codes were grouped together.
– The first two ASCII positions were reserved for control characters.
– The space character was placed before graphics for easier sorting.
– Lowercase letters were not interleaved with uppercase letters.
– The special and numeric codes were arranged before the letters.
Network Interchange and Limitations of ASCII
– The use of ASCII for Network Interchange was described in 1969.
– ASCII has 128 specified characters, with 95 printable characters.
– The original ASCII specification included 33 non-printing control codes.
– ASCII does not have a code point for the cent (¢) or support English terms with diacritical marks.
– ASCII also does not support proper nouns with diacritical marks.
ASCII Encoding and Binary Conversion
– ASCII values represent characters in binary.
– Binary-coded decimal simplifies conversion with ASCII.
– Non-alphanumeric characters correspond to typewriter positions.
– Some characters were shifted to accommodate European typewriters.
– Bit-paired keyboards, like the Teletype Model 33, used left-shifted layout.
– ASCII order is sometimes used for collation of data.
– Uppercase letters come before lowercase letters.
– Digits and punctuation marks come before letters.
– An intermediate order converts uppercase to lowercase before comparing.
– First 32 and last code points are reserved for control characters.
Control Characters, Line Termination, and End-of-File Indicators
– Control characters are used to control peripheral devices.
– Control codes like SOM, EOA, EOM, EOT, WRU, RU, DC0, SYNC, and ACK are essential for data transmission.
– Control characters do not represent printable characters.
– Placeholder symbols are assigned to control characters for debugging purposes.
– ASCII does not define mechanisms for text structure or appearance.
– Line termination refers to the character or sequence of characters used to mark the end of a line in a text file.
– Different operating systems and text editors have different conventions for line termination.
– The newline problem arose due to the ambiguity of control characters and differences in historical usage.
– Different operating systems and file systems used various characters or sequences to indicate the end of a file.
– Control-Z (SUB), control-C, and control-D were used as end-of-file indicators in different systems.
ASCII (/ˈæskiː/ ⓘ ASS-kee), 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 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.
 ASCII chart from MIL-STD-188-100 (1972) | |
| MIME / IANA | us-ascii |
|---|---|
| Alias(es) | ISO-IR-006, ANSI_X3.4-1968, ANSI_X3.4-1986, ISO_646.irv:1991, ISO646-US, us, IBM367, cp367 |
| Language(s) | English (made for; does not support all loanwords), Malay, Rotokas, Interlingua, Ido, and X-SAMPA |
| Classification | ISO/IEC 646 series |
| Extensions |
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| Preceded by | ITA 2, FIELDATA |
| Succeeded by | ISO/IEC 8859, ISO/IEC 10646 (Unicode) |
The Internet Assigned Numbers Authority (IANA) prefers the name US-ASCII for this character encoding.
ASCII is one of the IEEE milestones.
