Extended code utilization
Some character sets, including ASCII and EBCDIC, have the built-in capability to redefine characters through the utilization of Shift Out (SO) and Shift In (SI) characters. The Shift Out character, in effect, denotes that all characters following that character unit a Shift In (SI) character is encountered have new meanings represented by a new character set you have defined. Figure 2.6 illustrates the use of an extended code to implement run length compression. Note that the compressed data format now requires five characters. In comparison, the use of an existing character in the character set for the special compression-indicating character only required three characters. Thus, an extended code for run length compression would only be beneficial when a string of repeating characters exceeded five.