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A double-byte character set (DBCS) is a
character encoding Character encoding is the process of assigning numbers to Graphics, graphical character (computing), characters, especially the written characters of Language, human language, allowing them to be Data storage, stored, Data communication, transmi ...
in which either all characters (including control characters) are encoded in two bytes, or merely every
graphic character In ISO/IEC 646 (commonly known as ASCII) and related standards including ISO 8859 and Unicode, a graphic character is any character intended to be written, printed, or otherwise displayed in a form that can be read by humans. In other words, it i ...
not representable by an accompanying single-byte character set (
SBCS SBCS, or Single Byte Character Set, is used to refer to character encodings that use exactly one byte for each graphic character. An SBCS can accommodate a maximum of 256 symbols, and is useful for scripts that do not have many symbols or accented ...
) is encoded in two
bytes The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable uni ...
(
Han characters Chinese characters () are logograms developed for the writing of Chinese. In addition, they have been adapted to write other East Asian languages, and remain a key component of the Japanese writing system where they are known as ''kanji' ...
would generally comprise most of these two-byte characters). A DBCS supports national languages that contain many unique characters or symbols (the maximum number of characters that can be represented with one byte is 256 characters, while two bytes can represent up to
65,536 65536 is the natural number following 65535 and preceding 65537. 65536 is a power of two: 2^ (2 to the 16th power). 65536 is the smallest number with ''exactly'' 17 divisors. In mathematics 65536 is 2^, so in tetration notation 65536 is  ...
characters). Examples of such languages include Japanese and Chinese. Korean
Hangul The Korean alphabet, known as Hangul, . Hangul may also be written as following South Korea's standard Romanization. ( ) in South Korea and Chosŏn'gŭl in North Korea, is the modern official writing system for the Korean language. The let ...
does not contain as many characters, but
KS X 1001 KS X 1001, "''Code for Information Interchange (Hangul and Hanja)''", formerly called KS C 5601, is a South Korean coded character set standard to represent hangul and hanja characters on a computer. KS X 1001 is encoded by the most common le ...
supports both Hangul and
Hanja Hanja (Hangul: ; Hanja: , ), alternatively known as Hancha, are Chinese characters () used in the writing of Korean. Hanja was used as early as the Gojoseon period, the first ever Korean kingdom. (, ) refers to Sino-Korean vocabulary, wh ...
, and uses two bytes per character.


In CJK (Chinese/Japanese/Korean) computing

The term ''DBCS'' traditionally refers to a character encoding where each graphic character is encoded in two bytes. In an 8-bit code, such as
Big-5 Big-5 or Big5 is a Chinese character encoding method used in Taiwan, Hong Kong, and Macau for traditional Chinese characters. The People's Republic of China (PRC), which uses simplified Chinese characters, uses the GB 18030 character set ins ...
or
Shift JIS Shift JIS (Shift Japanese Industrial Standards, also SJIS, MIME name Shift_JIS, known as PCK in Solaris contexts) is a character encoding for the Japanese language, originally developed by a Japanese company called ASCII Corporation in conjunctio ...
, a character from the DBCS is represented with a lead (first) byte with the
most significant bit In computing, bit numbering is the convention used to identify the bit positions in a binary number. Bit significance and indexing In computing, the least significant bit (LSB) is the bit position in a binary integer representing the binary 1 ...
set (i.e., being greater than seven bits), and paired up with a single-byte character-set (SBCS). For the practical reason of maintaining compatibility with unmodified, off-the-shelf software, the SBCS is associated with half-width characters and the DBCS with
full-width character In CJK (Chinese, Japanese and Korean) computing, graphic characters are traditionally classed into fullwidth (in Taiwan and Hong Kong: 全形; in CJK: 全角) and halfwidth (in Taiwan and Hong Kong: 半形; in CJK: 半角) characters. Unlik ...
s. In a 7-bit code such as
ISO-2022-JP ISO/IEC 2022 ''Information technology—Character code structure and extension techniques'', is an ISO/ IEC standard (equivalent to the ECMA standard ECMA-35, the ANSI standard ANSI X3.41 and the Japanese Industrial Standard JIS X 0202) in the ...
,
escape sequences In computer science, an escape sequence is a combination of characters that has a meaning other than the literal characters contained therein; it is marked by one or more preceding (and possibly terminating) characters. Examples * In C and man ...
or shift codes are used to switch between the SBCS and DBCS. Sometimes, the use of the term "DBCS" can imply an underlying structure that does not comply with
ISO 2022 ISO/IEC 2022 ''Information technology—Character code structure and extension techniques'', is an ISO/ IEC standard (equivalent to the ECMA standard ECMA-35, the ANSI standard ANSI X3.41 and the Japanese Industrial Standard JIS X 0202) in the ...
. For example, "DBCS" can sometimes mean a double-byte encoding that is specifically not
Extended Unix Code Extended Unix Code (EUC) is a multibyte character encoding system used primarily for Japanese, Korean, and simplified Chinese. The most commonly used EUC codes are variable-length encodings with a character belonging to an compliant coded charac ...
(EUC). This original meaning of DBCS is different from what some consider correct usage today. Some insist that these character encodings be properly called
multi-byte character set A variable-width encoding is a type of character encoding scheme in which codes of differing lengths are used to encode a character set (a repertoire of symbols) for representation, usually in a computer. Most common variable-width encodings ar ...
s (MBCS) or
variable-width encoding A variable-width encoding is a type of character encoding scheme in which codes of differing lengths are used to encode a character set (a repertoire of symbols) for representation, usually in a computer. Most common variable-width encodings are ...
s, because character encodings such as
EUC-JP Extended Unix Code (EUC) is a multibyte character encoding system used primarily for Japanese, Korean, and simplified Chinese. The most commonly used EUC codes are variable-length encodings with a character belonging to an compliant coded charac ...
,
EUC-KR Extended Unix Code (EUC) is a multibyte character encoding system used primarily for Japanese, Korean, and simplified Chinese. The most commonly used EUC codes are variable-length encodings with a character belonging to an compliant coded char ...
,
EUC-TW Extended Unix Code (EUC) is a multibyte character encoding system used primarily for Japanese, Korean, and simplified Chinese. The most commonly used EUC codes are variable-length encodings with a character belonging to an compliant coded charac ...
,
GB 18030 GB 18030 is a Chinese government standard, described as ''Information Technology — Chinese coded character set'' and defines the required language and character support necessary for software in China. GB18030 is the registered Internet n ...
, and
UTF-8 UTF-8 is a variable-width encoding, variable-length character encoding used for electronic communication. Defined by the Unicode Standard, the name is derived from ''Unicode'' (or ''Universal Coded Character Set'') ''Transformation Format 8-bit'' ...
use more than two bytes for some characters, and they support one byte for other characters.


Ambiguity

Some people use DBCS to mean the
UTF-16 UTF-16 (16-bit computing, 16-bit Unicode Transformation Format) is a character encoding capable of encoding all 1,112,064 valid code points of Unicode (in fact this number of code points is dictated by the design of UTF-16). The encoding is variab ...
and
UTF-8 UTF-8 is a variable-width encoding, variable-length character encoding used for electronic communication. Defined by the Unicode Standard, the name is derived from ''Unicode'' (or ''Universal Coded Character Set'') ''Transformation Format 8-bit'' ...
encodings, while other people use the term DBCS to mean older (pre-
Unicode Unicode, formally The Unicode Standard,The formal version reference is is an information technology Technical standard, standard for the consistent character encoding, encoding, representation, and handling of Character (computing), text expre ...
) character encodings that use more than one byte per character.
Shift JIS Shift JIS (Shift Japanese Industrial Standards, also SJIS, MIME name Shift_JIS, known as PCK in Solaris contexts) is a character encoding for the Japanese language, originally developed by a Japanese company called ASCII Corporation in conjunctio ...
,
GB 2312 is a key official character set of the People's Republic of China, used for Simplified Chinese characters. GB2312 is the registered internet name for EUC-CN, which is its usual encoded form. ''GB'' refers to the Guobiao standards (国家标准 ...
and
Big5 Big-5 or Big5 is a Chinese character encoding method used in Taiwan, Hong Kong, and Macau for traditional Chinese characters. The People's Republic of China (PRC), which uses simplified Chinese characters, uses the GB 18030 character set inst ...
are a few character encodings that can contain more than one byte per character, but even using the term DBCS for these character encodings is incorrect terminology because these character encodings are really
variable-width encoding A variable-width encoding is a type of character encoding scheme in which codes of differing lengths are used to encode a character set (a repertoire of symbols) for representation, usually in a computer. Most common variable-width encodings are ...
s (as are both UTF-16 and UTF-8). Some IBM mainframes do have true DBCS code pages, which contain only the double byte portion of a multi-byte code page. If a person uses the term "DBCS enablement" for software
internationalization In economics, internationalization or internationalisation is the process of increasing involvement of enterprises in international markets, although there is no agreed definition of internationalization. Internationalization is a crucial strateg ...
, they are using ambiguous terminology. They either mean they want to write software for
East Asian East Asia is the eastern region of Asia, which is defined in both geographical and ethno-cultural terms. The modern states of East Asia include China, Japan, Mongolia, North Korea, South Korea, and Taiwan. China, North Korea, South Korea a ...
markets using older technology with code pages, or they are planning on using Unicode. Sometimes this term also implies
translation Translation is the communication of the Meaning (linguistic), meaning of a #Source and target languages, source-language text by means of an Dynamic and formal equivalence, equivalent #Source and target languages, target-language text. The ...
into an East Asian language. Usually "Unicode enablement" means internationalizing software by using Unicode, and "DBCS enablement" means using incompatible character encodings that exist between the various countries in East Asia for internationalizing software. Since Unicode, unlike many other character encodings, supports all the major languages in East Asia, it is generally easier to enable and maintain software that uses Unicode. DBCS (non-Unicode) enablement is usually only desired when much older operating systems or applications do not support Unicode.


TBCS

A triple-byte character set (TBCS) is a character encoding in which characters (including control characters) are encoded in three bytes.


See also

*
Variable-width encoding A variable-width encoding is a type of character encoding scheme in which codes of differing lengths are used to encode a character set (a repertoire of symbols) for representation, usually in a computer. Most common variable-width encodings are ...
*
DOS/V DOS/V is a Japanese computing initiative starting in 1990 to allow DOS on IBM PC compatibles with VGA cards to handle double-byte (DBCS) Japanese text via software alone. It was initially developed from PC DOS by IBM for its PS/55 machines (a ...


External links


Microsoft's definition of "double-byte character set"
* {{character encoding Character encoding