ASCIIextended

ASCIIextended is a term used in computing to describe the family of 8-bit encodings that extend the 7-bit ASCII character set. Since ASCII defines only 128 characters, many systems added an 8th bit to encode an additional 128 characters, creating a variety of “extended ASCII” schemes. There is no single standard called ASCIIextended; instead, numerous code pages and character sets emerged, each mapping the upper 128 values differently.

Common examples include the ISO/IEC 8859 family (such as Latin-1, Latin-2, and their successors), Windows-1252, and various IBM PC code pages (like 437 and 850) as well as Mac OS Roman. In practice, “extended ASCII” is often used informally to refer to any 8-bit encoding that uses the first 128 code points for ASCII and the remaining 128 for additional symbols, letters, or graphic characters. This diversity means that text encoded in one extended ASCII scheme may display incorrectly if interpreted under another scheme.

Modern software generally prefers Unicode, which unifies characters from virtually all writing systems. Unicode encodings such as UTF-8 preserve ASCII compatibility for the 0–127 range but encode other characters without relying on a fixed 128-entry extension scheme. The legacy use of extended ASCII can lead to compatibility problems in data exchange, file formats, and software localization if code pages are misaligned. Consequently, many systems migrate to Unicode while still occasionally encountering the historical notion of ASCIIextended in documentation and discussions of older software.