Halfwidth and fullwidth forms: Difference between revisions

Revision as of 14:50, 11 August 2022

Revision as of 10:37, 29 December 2022

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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 a [[SBCS]] (single-byte character set) was generally used to encode characters of Western languages.

For aesthetic reasons and readability, it is preferable for [[Han character]]s to be approximately square-shaped, thuslytherefore twice as wide as these fixed-width SBCS characters. As these were typically encoded in a [[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.

On the other hand, early Japanese computing used a single-byte code page called [[JIS X 0201]] for [[katakana]]. These would be rendered at the same width as the other single-byte characters, making them [[half-width kana]] characters rather than normally proportioned kana. Although the JIS X 0201 standard itself did not specify half-width display for katakana, this became the visually distinguishing feature in [[Shift JIS]] between the single-byte JIS X 0201 and double-byte [[JIS X 0208]] katakana. Some IBM code pages used a similar treatment for [[Hangul#Letters|Korean jamo]],<ref name="ibm933">{{cite web|url=http://demo.icu-project.org/icu-bin/convexp?conv=ibm-933|title=ICU Demonstration - Converter Explorer|website=demo.icu-project.org|access-date=7 May 2018}}</ref> based on the [[KS C 5601#1974|N-byte Hangul code]] and its [[EBCDIC]] translation.