UCS-2 and its relationship to Unicode

Because the UCS-2 standard is limited to 65 535 characters, and the data processing industry needs over 94 000 characters, the UCS-2 standard is in the process of being superseded by the Unicode UTF-16 standard.

Because UTF-16 is a superset of the existing UCS-2 standard, you can develop your applications using the existing UCS-2 support as long as your applications treat the UCS-2 as if it were UTF-16.

i5/OS™ supports UCS-2 encoding with CCSID 13488.

UCS, UCS-2 (Universal Multiple-Octet Coded Character Set)

The ISO 10646 standard is a character code designed to encode text for storage in computer files. The design of the ISO 10646 standard is based on today's prevalent character code, ASCII (and ISO 8859-1, an extended version of the ASCII code). But ISO 10646 goes beyond ASCII's ability to encode only the Latin alphabet. The ISO 10646 encoding provides the capability to encode all of the characters used for written languages throughout the world.

Two UCS encoding schemes

In order to accommodate the many thousands of characters used in international text, ISO/IEC 10646 specifies the Universal Multiple-Octet Coded Character Set (UCS). UCS can be implemented through two encoding schemes:

UCS-2: Each character is represented by 16 bits or 2 bytes. (The number 2 in UCS-2 indicates 2 bytes.) For example, uppercase A is represented by 0041.

UCS-4: Each character is represented by 32 bits or 4 bytes. (The number 4 in UCS-4 indicates 4 bytes.) For example, uppercase A is represented by 0000 0041.

The major difference between the 2-byte and 4-byte representation is that the 4-byte representation allows for the presentation or use of additional characters beyond the capability of UCS-2. That is, you can encode more characters in UCS-4 than you can in UCS-2.

i5/OS does not support UCS-4 encoding with a CCSID value.