English: Basic structure of the Unified Hangul Code (UHC), also called Windows-949 or IBM-1363.

The single byte region does not accept a second byte, hence it is shown occupying the entire width of the encoding space diagram. It is either treated as ISO-646-KR (defined by KS C 5636, later renamed KS X 1003), e.g. in localised fonts or IBM's Unicode mapping, or treated as US-ASCII, e.g. in Unicode mapping on Windows.

Standard Wansung codes (as originally defined by KS C 5601:1987, now called KS X 1001:1987) are represented the same as in EUC-KR, i.e. as their ISO 2022 codes designated to GR. Wansung (unlike e.g. the Johab code defined by KS C 5601:1992 annex 3) only encodes the most common Hangul syllables precomposed, not all that could conceivably be required (although it does allow the others to be represented by four-character combining sequences in which the first character is a Hangul Filler). The extended Hangul region encodes all other possible modern-Jamo Hangul syllables in Unicode order, but with those already present in Wansung code skipped. Gaps in the extended Hangul region are due to UHC not using non-alphabetical ASCII bytes as trail bytes. 0x80 and Eight Ones (0xFF) are never used as a lead or trail byte (although they might get best-fit mapped to U+0080 and private use U+F8F7 respectively).

See also:

• The WHATWG provide a nice code chart for the double-byte region of what they call "EUC-KR" (but which is actually the entirety of UHC). Warning: Very large HTML table.
• ICU demonstration for Windows-949 (with ASCII mappings)
• ICU demonstration for IBM-1363 (with ISO 646:KR mappings)

Wansung, Johab and UHC are South Korean encodings. With respect to North Korea, the encoded form of KPS 9566:2003 documented by the Unicode Consortium appears to use a similar and most probably strongly inspired structure, but with a updated revision of KPS 9566:1997 (the DPRK equivalent of Wansung code) in the EUC region, and with a different sequence in the extended Hangul region (due to the Hangul repertoire of KPS 9566:1997 not being the same as that of Wansung, and due to North Korea using a different ordering of the jamo).

Contrast with File:IBM Korea KS PC-Data encoding (IBM-949).svg, which is the IBM-949 encoding, serving to illustrate the different meanings of "code page 949" between Microsoft and IBM (the extensions are mutually incompatible and the common subset is basically just EUC-KR; Windows-949 corresponds to IBM-1363). Also worth comparing and contrasting with File:GBK encoding.svg, another encoding which extends the double byte repertoire of an EUC base encoding, but which takes a different approach in some ways.