Half-width Kana - Encoding

Encoding

In the JIS X 0201 specification (1969), katakana are encoded in A0–DF (hexadecimal) block – how they are displayed is not specified, and there is no separate encoding of full-width and half-width kana. In JIS X 0208, katakana, hiragana, and kanji are all encoded (and displayed as full-width characters; there are no half-width characters), though the ordering of the kana is different – see JIS X 0208#Hiragana and katakana.

In Shift JIS, which combines JIS X 0201 and JIS X 0208, these encodings (both of which can encode Latin characters and katakana) are stored separately, with JIS X 0201 all being displayed as half-width (thus the JIS X 0201 katakana are displayed as half-width kana), while JIS X 0208 are all displayed as full-width (thus the JIS X 0208 Latin characters are all displayed as full-width Latin characters). Thus in Shift JIS, Latin characters and katakana have two encodings with two separate display forms, both half-width and full-width.

In Unicode, katakana and hiragana are primarily used as normal, full-width characters (the Katakana and Hiragana blocks are displayed as full-width characters); a separate block, the Halfwidth and Fullwidth Forms block is used to store variant characters, including half-width kana and full-width Latin characters.

Thus, the katakana in JIS X 0201 and the corresponding part of derived encodings (the JIS X 0201 part of Shift JIS) are displayed as half-width, while in Unicode half-width forms are specified separately.