Halfwidth and fullwidth forms: Difference between revisions

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{{For|the Unicode block|Halfwidth and Fullwidth Forms (Unicode block)}}

[[File:Command Prompt on Windows XP (Korean).png|thumb|349px|A command prompt ([[cmd.exe]]) with Korean localisation, showing halfwidth and fullwidth characters]]

VampireIn [[CJK characters|CJK]] (Chinese, Japanese, and Korean) computing, [[graphic character]]s are traditionally classed into '''fullwidth'''{{efn|In [[Taiwan]] and [[Hong Kong]]: [[wikt:全形|全形]]; in CJK: [[wikt:全角|全角]].}} and '''halfwidth'''{{efn|In [[Taiwan]] and [[Hong Kong]]: [[wikt:半形|半形]]; in CJK: [[wikt:半角|半角]].}} characters. Unlike [[monospaced font]]s, a halfwidth character occupies half the width of a fullwidth character, hence the name.

''[[Halfwidth and Fullwidth Forms (Unicode block)|Halfwidth and Fullwidth Forms]]'' is also the name of a [[Unicode block]] U+FF00–FFEF, provided so that older encodings containing both halfwidth and fullwidth characters can have lossless translation to and from Unicode.

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{{More citations needed section|date=April 2021}}

[[File:Alternative names of JIS X 0213.svg|thumb|Characters which appear in both [[JIS X 0201]] (single byte) and [[JIS X 0208]] / [[JIS X 0213]] (double byte) have both a halfwidth and a fullwidth form in [[Shift JIS]].|class=skin-invert]]

In the days of [[text mode]] computing, Western characters were normally laid out in a grid on the screen, often 80 columns by 24 or 25 lines. Each character was displayed as a small [[dot matrix]], often about 8 [[pixel]]s wide, and aan [[SBCS]] (single-byte character set) was generally used to encode characters of Western languages.

For aesthetic reasons and readability, it is preferable for [[Chinese characters]] to be approximately square-shaped, therefore twice as wide as these fixed-width SBCS characters. As these were typically encoded in a [[double-byte character set|DBCS]] (double-byte character set), this also meant that their width on screen in a [[duospaced font]] was proportional to their byte length. Some terminals and editing programs could not deal with double-byte characters starting at odd columns, only even ones (some could not even put double-byte and single-byte characters in the same line). So the DBCS sets generally included Roman characters and digits also, for use alongside the CJK characters in the same line.