Overview
Code page 942 (CP 942) is a double‑byte character set (DBCS) employed primarily by IBM operating systems to represent Japanese text. It is based on the Shift JIS encoding scheme and incorporates additional characters defined by IBM for compatibility with legacy IBM applications and hardware. As a proprietary extension of the standard Shift JIS, CP 942 enables the encoding of both the standard Japanese characters (kanji, hiragana, katakana) and a set of IBM‑specific symbols and glyphs.
Technical Characteristics
| Feature | Description |
|---|---|
| Encoding type | Double‑byte character set (DBCS) derived from Shift JIS |
| Single‑byte range | 0x00–0x7F (identical to ASCII) and 0xA1–0xDF (half‑width katakana) |
| Lead‑byte ranges | 0x81–0x9F and 0xE0–0xFC; these combine with trail bytes 0x40–0x7E and 0x80–0xFC to form double‑byte characters |
| Character repertoire | Includes the full set of JIS X 0208 kanji, JIS X 0201 kana, and a collection of IBM‑defined extensions (e.g., additional symbols, corporate logos, and vendor‑specific glyphs) |
| Mapping to Unicode | Each CP 942 code point can be mapped to a corresponding Unicode code point; the mapping aligns with the Unicode block for CJK Unified Ideographs, Katakana, and the Private Use Area for IBM‑specific characters |
| Supported platforms | Historically used on IBM AIX, IBM i (formerly OS/400), OS/2, and other IBM mid‑range/mainframe environments |
| Relation to other code pages | CP 942 is a superset of IBM code page 932 (the standard Shift JIS implementation on Windows) and is closely related to CP 943, which adds further extensions for NEC selected characters. |
Historical Context
During the late 1980s and 1990s, IBM adopted CP 942 to provide a Japanese encoding compatible with its existing software ecosystem while preserving the ability to represent specialized characters required by IBM’s proprietary applications. The code page allowed seamless interchange of Japanese text between IBM mainframe, AS/400, and UNIX (AIX) systems before the widespread adoption of Unicode.
Current Usage
With the global transition toward Unicode (UTF‑8, UTF‑16) for multilingual text processing, the practical use of CP 942 has declined. Nevertheless, legacy IBM systems and applications that have not been migrated continue to rely on CP 942 for file encoding, database storage, and terminal communication. Modern IBM software supplies conversion utilities to map CP 942 data to Unicode and vice versa.
Standardization and Documentation
IBM’s official documentation—such as the IBM Knowledge Center and IBM International Technical Reference Manuals—provides definitive tables of CP 942 code point assignments and conversion rules. These sources constitute the primary authoritative references for the code page.
See Also
- Shift JIS
- IBM code page 932
- IBM code page 943
- Unicode
- Japanese Industrial Standards (JIS) X 0201, X 0208
References
- IBM Knowledge Center, “Code page 942 (CP942) – Japanese (Shift JIS) with IBM extensions.”
- IBM System i Information Center, “Character encoding and conversion on IBM i.”
Note: The information presented reflects documented IBM specifications. Where specific character mappings or IBM‑exclusive glyph definitions are not publicly disclosed, the entry indicates the general nature of the extensions without enumerating each proprietary symbol.