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More on CJK Character Sets and Encoding Forms

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Definitions

Character Set
An abstract notion of a list of characters in a specified order.
Encoding
The encoding of a character set is how its characters are represented in bits and bytes.  A character set may be encoded in different encoding forms.
7-bit Encoding
Each character is encoded in one or more bytes depending on the size of the character set.  Each byte is 8-bit long but the first bit is set to zero, so there are only 7 variable bits.  Some bytes, reserved for other purposes, may not be used to encode printable characters.  The best known 7-bit encoded character set is ASCII, in which every character is encoded in exactly one byte.  E-mail messages are usually sent in 7-bit encoding because 8-bit or 16-bit encoded characters may not pass correctly through some gateways.
8-bit Encoding
Each character is encoded in one or more bytes depending on the size of the character set.  All 8 bits are variable but some bytes, reserved for other purposes, may not be used to encode printable characters.  The vast marjority of web pages is written in 8-bit encoding.
16-bit Encoding
Each character is encoded in one or more pairs of bytes.  Some pairs of bytes may not be be used to encode printable characters but any byte may occur within a pair.  UTF-16, the default transformation format of Unicode is a 16-bit encoding form.
Single-Byte Character Set
Each character of a SBCS is encoded in exactly one byte.  7-bit encoded ASCII and the 8-bit encoded pre-Unicode Western, Greek, Cyrillic etc. character sets are Single-Byte Character Sets.
Double-Byte Character Set
A cover term for pre-Unicode CJK character sets.  Each character of a DBCS is encoded in exactly two bytes.  A DBCS is always encoded along with a 7-bit Single-Byte Character Set such as ASCII or a variant thereof, which results in a mixed system of double-byte and single-byte encoded characters.
94x94 Character Set
A DBCS whose characters are arranged in a matrix of  94 rows and 94 columns and are identified by their row-cell numbers (Japanese kuten.gif kuten, Chinese quwei.gif qu1wei4).
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© Gyula Zsigri [CJK]  [Home] June 29, 2001