GBK (character encoding)#Encoding

In 1993, the Unicode 1.1 standard was released, including 20,902 characters used in mainland China, Taiwan, Japan and Korea. Following this, China released {{nowrap|GB 13000.1-93}}, the Guobiao standard equivalent of Unicode 1.1.

{{anchor|1993}}The GBK character set was defined in 1993 as an extension of {{nowrap|GB 2312-80}}, while also including the characters of GB 13000.1-93 through the unused codepoints available in GB 2312. Hence GBK is backward compatible with GB 2312. GBK was defined in a normative annex to GB 13000.1-93.{{cite web |url=https://www.unicode.org/versions/Unicode15.0.0/ch18.pdf#page=28 |p=763 |title=18.2: Ideographic Description Characters |work=The Unicode Standard |version=Version 15.0.0 |year=2022 |quotation=The Ideographic Description characters are found in GBK—an extension to GB 2312-80 that added all 20,902 Unicode Version 1.1 ideographs not already in GB 2312-80. GBK is defined as a normative annex of GB 13000.1-93.}}

{{anchor|cp936}}Microsoft implemented GBK in Windows 95 and Windows NT 3.51 as Code Page 936. While GBK was never an official standard, widespread usage of Windows 95 led to GBK becoming the de facto standard. While GBK included all the Chinese characters defined in Unicode 1.1 and GB 13000.1-93, these standards used different code tables. The primary reason for its existence was simply to bridge the gap between GB 2312-80 and GB 13000.1-93.

{{anchor|GBK 1.0}}In 1995, China National Information Technology Standardization Technical Committee set down the Chinese Internal Code Extension Specification ({{lang-zh|s=汉字内码扩展规范 (GBK)|p=Hànzì Nèimǎ Kuòzhǎn Guīfàn (GBK)}}), Version 1.0, known as GBK 1.0, which is a slight extension of Codepage 936. The newly added 95 characters were not found in GB 13000.1-1993, and were provisionally assigned Unicode PUA code points.{{Cite book|url=https://archive.org/details/GB18030-2005|title=GB 18030-2005: Information Technology—Chinese coded character set|last=Standardization Administration of China (SAC)|date=2005-11-18}}{{Rp|534}}

Microsoft later added the euro sign to Code page 936 and assigned the code 0x80 to it. This is not a valid code point in GBK 1.0.

In 2000, the {{nowrap|GB 18030-2000}} standard was released, superseding yet maintaining compatibility with GBK 1.0. It increased the number of definitions of Chinese characters and extended the number of possible characters through the implementation of four-byte character spaces. The subset of GB 18030 consisting of one-byte and two-byte characters is sometimes also referred to as GBK. Mapping to Unicode has been slightly changed, though, as some characters are now defined in Unicode. In the most up-to-date form of the standard, GB 18030-2005, only 24GB 18030-2005 Standard p.9, 79 characters are still mapped to Unicode PUA (see GB 18030#PUA.)

In 2002, GBK was registered as an IANA charset; the registration uses code page 936 mapping as well as CP936/MS936 aliases, but refers to GBK 1.0 specification. {{anchor|W3C}}W3C's technical recommendation published in 2015{{cite web|title=Encoding Standard # gbk-encoder|url=https://www.w3.org/TR/encoding/#gbk-encoder|website=W3C|access-date=2016-10-02}} defines a GBK encoder as a GB 18030 encoder with a single-byte euro sign and without four-byte sequences (while W3C's GBK decoder specification has no such limitation, decodes as {{nowrap|GB 18030}}, i.e. with same range of letters as all of Unicode).

A character is encoded as 1 or 2 bytes. A byte in the range 00–7F is a single byte that means the same thing as it does in ASCII. Strictly speaking, there are 95 characters and 33 control codes in this range.

A byte with the high bit set indicates that it is the first of 2 bytes. Loosely speaking, the first byte is in the range 81–FE (that is, never 80 or FF), and the second byte is 40–A0 except 7F for some areas and A1–FE for others.

More specifically, the following ranges of bytes are defined:

In graphical form, the following figure shows the space of all 64K possible 2-byte codes. Green and yellow areas are assigned GBK codepoints, red are for user-defined characters. The uncolored areas are invalid byte combinations.

Image:GBK encoding.svg

The areas indicated in the previous section as GBK/1 and GBK/2, taken by themselves, is simply {{nowrap|GB 2312-80}} in its usual encoding, GBK/1 being the non-hanzi region and GBK/2 the hanzi region. GB 2312, or more properly the EUC-CN encoding thereof, takes a pair of bytes from the range A1–FE, like any 94² ISO-2022 character set loaded into GR. This corresponds to the lower-right quarter of the illustration above. However, GB 2312 does not assign any code points to the rows located at AA–B0 and F8–FE, even though it had staked out the territory. GBK added extensions to these rows. You can see that the two gaps were filled in with user-defined areas.

More significantly, GBK extended the range of the bytes. Having two-byte characters in the ISO-2022 GR range gives a limit of 94²=8,836 possibilities. Abandoning the ISO-2022 model of strict regions for graphics and control characters, but retaining the feature of low bytes being 1-byte characters and pairs of high bytes denoting a character, you could potentially have 128²=16,384 positions. GBK takes part of that, extending the range from A1–FE (94 choices for each byte) to 81–FE (126 choices) for the first byte and 40–FE (191 choices) for the second byte, for a total of 24,066 positions.

Microsoft's Code Page 936 is generally thought of as being GBK. However, the 95 PUA characters added in GBK 1.0 are not included in Code Page 936. Code Page 936 also has a single-byte euro sign at 0x80 which GBK 1.0 doesn't have.{{cite web |last1=Scherer |first1=Markus |title=Re: Fun with GBK & GB2312 |url=http://unicode.org/mail-arch/unicode-ml/y2002-m01/0042.html |website=Unicode Mail List Archive |access-date=4 March 2020 |date=4 January 2002}}

GBK's successor, {{nowrap|GB 18030-2000}}, uses the remaining range available to the second byte ({{code|30}}–{{code|39}}) to further expand the number of possibilities while retaining GBK as a subset.

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• [https://www.unicode.org/irg/docs/n0278-GBKv1.pdf A scan of the GBK 1.0 specification] provided by the Ideographic Research Group
• [http://icu-project.org/repos/icu/data/trunk/charset/source/gb18030/gbkuni30.txt ICU's Authoritative GBK mapping] - part of [https://ssl.icu-project.org/repos/icu/data/trunk/charset/source/gb18030/gb18030.html GB18030 data] {{Webarchive|url=https://web.archive.org/web/20161031024951/https://ssl.icu-project.org/repos/icu/data/trunk/charset/source/gb18030/gb18030.html |date=2016-10-31 }}
• [http://www.microsoft.com/globaldev/reference/dbcs/936.mspx Microsoft Reference page for GBK]
• [https://www.unicode.org/Public/MAPPINGS/VENDORS/MICSFT/WINDOWS/CP936.TXT Mapping of GBK to Unicode ] N.B.: this is Microsoft code page 936, which contains entries for 21791 double-byte code points, 96 single-byte graphic characters, and 33 control characters. This is not exactly the same as GBK which has 21886 characters.
• [http://www.khngai.com/chinese/charmap/tblgbk.php?page=0 GBK Code Table] N.B. This gbk-encoded page shows the available coding space totally populated except for 2 places, for a total of 32256 glyphs (32352 with the implied single-byte ASCII codes not illustrated), which is more than 23940 or 21886. Actual rendering of this table depends on your browser's GBK decoder.

{{CJK computing}}

{{Character encoding}}

Category:Windows code pages

Category:Chinese character encodings