ASCII

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.