What different encodings are there?
Both the UCS and Unicode standards are first of all large tables that assign to every character an integer number. If you use the term “UCS”, “ISO 10646”, or “Unicode”, this just refers to a mapping between characters and integers. This does not yet specify how to store these integers as a sequence of bytes in memory. ISO 10646-1 defines the UCS-2 and UCS-4 encodings. These are sequences of 2 bytes and 4 bytes per character, respectively. ISO 10646 was from the beginning designed as a 31-bit character set (with possible code positions ranging from U-00000000 to U-7FFFFFFF), however it took until 2001 for the first characters to be assigned beyond the Basic Multilingual Plane (BMP), that is beyond the first 216 character positions (see ISO 10646-2 and Unicode 3.1). UCS-4 can represent all UCS and Unicode characters, UCS-2 can represent only those from the BMP (U+0000 to U+FFFF). “Unicode” originally implied that the encoding was UCS-2 and it initially didn’t make any provisions for char
Both the UCS and Unicode standards are first of all large tables that assign to every character an integer number. If you use the term “UCS”, “ISO 10646”, or “Unicode”, this just refers to a mapping between characters and integers. This does not yet specify how to store these integers as a sequence of bytes in memory. ISO 10646-1 defines the UCS-2 and UCS-4 encodings. These are sequences of 2 bytes and 4 bytes per character, respectively. ISO 10646 was from the beginning designed as a 31-bit character set (with possible code positions ranging from U-00000000 to U-7FFFFFFF), however only very recently characters have been assigned beyond the Basic Multilingual Plane (BMP), that is beyond the first 216 character positions (see ISO 10646-2 and Unicode 3.1). UCS-4 can represent all UCS and Unicode characters, UCS-2 can represent only those from the BMP (U+0000 to U+FFFF). “Unicode” originally implied that the encoding was UCS-2 and it initially didn’t make any provisions for characters out
Both the UCS and Unicode standards are first of all large tables that assign to every character an integer number. If you use the term “UCS”, “ISO 10646”, or “Unicode”, this just refers to a mapping between characters and integers. This does not yet specify how to store these integers as a sequence of bytes in memory. ISO 10646-1 defines the UCS-2 and UCS-4 encodings. These are sequences of 2 bytes and 4 bytes per character, respectively. ISO 10646 was from the beginning designed as a 31-bit character set (with possible code positions ranging from U-00000000 to U-7FFFFFFF), however it took until 2001 for the first characters to be assigned beyond the Basic Multilingual Plane (BMP), that is beyond the first 216 character positions (see ISO 10646-2 and Unicode 3.1). UCS-4 can represent all UCS and Unicode characters, UCS-2 can represent only those from the BMP (U+0000 to U+FFFF). “Unicode” originally implied that the encoding was UCS-2 and it initially didn’t make any provisions for char
