Evolving standards based on limited platforms
The representation of character data in modern computer systems can be fairly complicated, depending on the needs of your globalized application. One of the reasons for this complexity is that the methods for handling this data have evolved from early methods that served less complicated environments and hardware platforms.
In fact, many early decisions about how to encode characters on a system were guided by the functional requirements of specific devices, such as the early Telex (TTY) terminals and punch card technologies. For example, the Delete character (with an ASCII value of x'7F') was required in order to punch out all of the holes in a column of a punch card to signify that the column should be ignored. The storage capacities of these early computing systems placed additional limitations on system and application designers.
- The ASCII (American Standard Code for Information Interchange) character set uses 7-bit units, with a trivial encoding designed for 7-bit bytes. It is the most important character set in use today, despite its limitation to very few characters, because its design is the foundation for most modern character sets. ASCII provides only 128 numeric values, and 33 of those are reserved for special functions.
- The EBCDIC (Extended Binary-Coded Decimal Interchange Code) character set and a number of associated character sets, designed by IBM for its mainframes, uses 8-bit bytes. It was developed at a similar time as ASCII, and shares the same set of base characters and has other similar properties. Unlike ASCII, the Latin letters are not combined in two blocks for upper- and lower-case. Instead, the letters are arranged so that their hexadecimal values have second digits of 1 through 9.