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International Language Environments Guide

Unicode Overview

The Unicode Standard is the universal character encoding standard used for representation of text for computer processing. It is fully compatible with the international standards ISO/IEC 10646-1:2000 and ISO/IEC 10646–2:2001, and contains all the same characters and encoding points as ISO/IEC 10646. The Unicode Standard provides additional information about the characters and their use. Any implementation that conforms to Unicode also conforms to ISO/IEC 10646.

The Unicode Standard provides a consistent way of encoding multilingual plain text and facilitates exchanging international text files. Computer users who deal with multilingual text, business people, linguists, researchers, scientists, and others find that the Unicode Standard greatly simplifies their work. Mathematicians and technicians, who regularly use mathematical symbols and other technical characters, also find the Unicode Standard valuable.

The maximum possible number of code points Unicode can support is 1,114,112 through seventeen 16-bit planes. Each plane can support 65,536 different code points.

Among the more than one million code points that Unicode can support, version 3.1 currently defines 94,140 characters at plane 0, 1, 2, and 14. Planes 15 and 16 are for private use, also known as user-defined characters. Planes 15 and 16 together can support total 131,068 user-defined characters.

Unicode can be encoded using any of the following character encoding schemes:

UTF-8 is a variable-length encoding form of Unicode that preserves ASCII character code values transparently. This form is used as file code in Solaris Unicode locales.

UTF-16 is a 16-bit encoding form of Unicode. In UTF-16, characters up to 65,535 are encoded as single 16-bit values. Characters mapped above 65,535 to 1,114,111 are encoded as pairs of 16-bit values (surrogates).

UTF-32 is a fixed-length, 21-bit encoding form of Unicode usually represented in a 32-bit container or data type. This form is used as the process code (wide-character code) in Solaris Unicode locales.

For more details on the Unicode Standard and ISO/IEC 10646 and their various representative forms, refer to: