JIS X 0208


JIS X 0208 is a 2-byte character set specified as a Japanese Industrial Standard, containing 6879 graphic characters suitable for writing text, place names, personal names, and so forth in the Japanese language. The official title of the current standard is 7-bit and 8-bit double byte coded KANJI sets for information interchange. It was originally established as JIS C 6226 in 1978, and has been revised in 1983, 1990, and 1997. It is also called Code page 952 by IBM. The 1978 version is also called Code page 955 by IBM.

Scope of use and compatibility

The character set JIS X 0208 establishes is primarily for the purpose of information interchange between data processing systems and the devices connected to them, or mutually between data communication systems. This character set can be used for data processing and text processing.
Partial implementations of the character set are not considered compatible. Because there are places where such things have happened as the original drafting committee of the first standard taking care to separate characters between level 1 and level 2 and the second standard then shuffling some variant characters between the levels, at least in the first and second standards, it is conjectured that non-kanji and level 1-only implementation Japanese computer systems were at one time considered for development. However, such implementations have never been specified as compatible, though an example like the early NEC PC-9801 did exist.
Even though there are provisions in the JIS X 0208:1997 standard concerning compatibility, at the present time, it is generally considered that this standard neither certifies compatibility nor is it an official manufacturing standard that amounts to a declaration of self-compatibility. Consequently, de facto, JIS X 0208-"compatible" products are not considered to exist. Terminology such as "conformant" and "support" is included in JIS X 0208, but the semantics of these terms vary from person to person.

Code charts

Lead byte

The first encoding byte corresponds to the row or cell number plus 0x20, or 32 in decimal. Hence, the code set starting with 0x21 has a row number of 1, and its cell 1 has a continuation byte of 0x21, and so forth.

Non-Kanji rows

Character set 0x21 (row number 1, special characters)

Some vendors use slightly different Unicode mapping for this set than the one [|below]. For example, Microsoft maps kuten 1-29 to U+2015, whereas Apple maps it to U+2014. Similarly, Microsoft maps kuten 1-61 to U+FF0D, and Apple maps it to U+2212. Unicode mapping of the wave dash also differs between vendors. See the cells with footnotes below.
ASCII and JISCII punctuation may use alternative mappings to the Halfwidth and Fullwidth Forms block if used in an encoding which combines JIS X 0208 with ASCII or with JIS X 0201, such as Shift JIS, EUC-JP or ISO 2022-JP.

Character set 0x22 (row number 2, special characters)

Most of the characters in this set were added in 1983, except for characters 0x2221-0x222E, which were included in the original 1978 version of the standard.

Character set 0x23 (row number 3, digits and Roman)

This set includes a subset of the ISO 646 invariant set, minus punctuation and symbols, comprising western Arabic numerals and both cases of the Basic Latin alphabet. Characters in this set may use alternative Unicode mappings to the Halfwidth and Fullwidth Forms block if used in an encoding which combines JIS X 0208 with ASCII or with JIS X 0201, such as EUC-JP, Shift JIS or ISO 2022-JP.
Compare row 3 of KPS 9566, which this row exactly matches. Compare and contrast row 3 of KS X 1001 and GB 2312, which include their entire national variants of ISO 646 in this row, rather than only the alphanumeric subset.

Character set 0x24 (row number 4, Hiragana)

This row contains Japanese Hiragana.
Compare and contrast row 10 of KPS 9566 and of KS X 1001, which use the same layout, but in a different row.

Character set 0x25 (row number 5, Katakana)

This row contains Japanese Katakana.
Compare and contrast row 11 of KPS 9566 and of KS X 1001, which use the same layout, but in a different row. Contrast the different Katakana layout used by JIS X 0201.

Character set 0x26 (row number 6, Greek)

This row contains basic support for the modern Greek alphabet, without diacritics or the final sigma.
Compare row 6 of KPS 9566, which includes the same Greek letters in the same layout, but adds Roman numerals after them. Compare and contrast row 5 of KS X 1001, which offsets the Greek letters to include the Roman numerals first.

Character set 0x27 (row number 7, Cyrillic)

This row contains the modern Russian alphabet and is not necessarily sufficient for representing other forms of the Cyrillic script.
Compare row 12 of KS X 1001 and row 5 of KPS 9566, which use the same layout.

Character set 0x28 (row number 8, box drawing)

All characters in this set were added in 1983, and were not present in the original 1978 revision of the standard.

Extension character set 0x2D (row number 13, NEC special characters)

Rows 9 through 15 of the JIS X 0208 standard are left empty.
However, the following layout for row 13, first introduced by NEC, is a common extension. It is used by Windows-932, by the PostScript variant of MacJapanese, and by [|JIS X 0213]. Unlike the other extensions made by Windows-932/WHATWG and JIS X 0213, the two match rather than colliding, so decoding of most of this row is better supported than the other extensions made by JIS X 0213.

Kanji rows

Code structure

In order to represent code points, column/line numbers are used for one-byte codes and kuten numbers are used for two-byte codes. For a way to identify a character without depending on a code, character names are used.

Single byte codes

Almost all JIS X 0208 graphic character codes are represented with two bytes of at least seven bits each. However, every control character, as well as the plain space - although not the ideographic space - is represented with a one-byte code. In order to represent the bit combination of a one-byte code, two decimal numbers – a column number and a line number – are used. Three high-order bits out of seven or four high-order bits out of eight, counting from zero to seven or from zero to fifteen respectively, form the column number. Four low-order bits counting from zero to fifteen form the line number. Each decimal number corresponds to one hexadecimal digit. For example, the bit combination corresponding to the graphic character "space" is 010 0000 as a 7-bit number, and 0010 0000 as an 8-bit number. In column/line notation, this is represented as 2/0. Other representations of the same single-byte code include 0x20 as hexadecimal, or 32 as a single decimal number.

Code points and code numbers

The double-byte codes are laid out in 94 numbered groups, each called a row. Every row contains 94 numbered codes, each called a cell. This makes a total of 8836 possible code points ; these are laid out in the standard in a 94-line, 94-column code table.
A row number and a cell number form a kuten point, which is used to represent double-byte code points. A code number or kuten number is expressed in the form "row-cell", the row and cell numbers being separated by a hyphen. For example, the character " instead uses the range 0xA1 through 0xFE, whereas other encodings such as Shift JIS use more complicated transforms. Shift JIS includes more encoding space than is needed for JIS X 0208 itself; some Shift JIS specific extensions to JIS X 0208 make use of row numbers [|above] 94.
This structure is also used in the Mainland Chinese GB 2312 and the South Korean KS C 5601. The later JIS X 0213 extends this structure by having more than one plane of rows, which is also the structure used by CNS 11643.

Unassigned code points

Among the 2-byte codes, rows 9 to 15 and 85 to 94 are unassigned code points; that is, they are code points with no characters assigned to them. Also, some cells in other rows are also essentially unassigned code points.
These empty areas contain code points that should basically not be used. Except when there is prior agreement among the relevant parties, characters for information interchange should not be assigned to the unassigned code points.
Even when assigning characters to unassigned code points, graphic characters defined in the standard should not be assigned to them, and the same character should not be assigned to multiple unassigned code points; characters should not be duplicated in the set.
Furthermore, when assigning characters to unassigned code points, it is necessary to be cautious of unification in regards to kanji glyphs. For example, row 25 cell 66 corresponds to the kanji meaning "high" or "expensive"; both the form with a component resembling the "mouth" character in the middle and the less common form with a ladder-like construction in the same location are subsumed into the same code point. Consequently, limiting point 25-66 to the "mouth" form and assigning the latter "ladder" form to an unassigned code point would technically be in violation of the standard.
In practice, however, several vendor-specific Shift JIS variants, including Windows-932 and MacJapanese, encode vendor extensions in unallocated rows of the encoding space for JIS X 0208. Also, most of the codes unassigned in JIS X 0208 are assigned by the newer JIS X 0213 standard.

Character names

Each JIS X 0208 character is given a name. By using a character's name, it is possible to identify characters without relying on their codes. The names of characters are coordinated with other character set standards, notably the Universal Coded Character Set, so this is one possible source of character mappings to character sets such as Unicode. For example, both the character at ISO/IEC 646 International Reference Version column 4 line 1 and the one at JIS X 0208 row 3 cell 33 have the name "LATIN CAPITAL LETTER A". Therefore, the character at 4/1 in ASCII and the character at 3-33 in JIS X 0208 can be regarded as the same character. Conversely, ASCII characters 2/2, 2/7, 2/13, and 7/14 can be determined to be characters that do not exist in this standard.
Character names of non-kanji characters use uppercase Roman letters, spaces, and hyphens. Non-kanji characters are given a Japanese-language common name, but some provisions for these names do not exist. The names of kanji, on the other hand, are mechanically set according to the corresponding hexadecimal representation of their code in UCS/Unicode. The name of a kanji can be arrived at by prepending the Unicode codepoint with "CJK UNIFIED IDEOGRAPH-". For example, row 16 cell 1 corresponds to U+4E9C in UCS, so the name of it would be "CJK UNIFIED IDEOGRAPH-4E9C". Kanji are not given Japanese common names.

Kanji set

Overview

JIS X 0208 prescribes a set of 6879 graphical characters that correspond to two-byte codes with either seven or eight bits to the byte; in JIS X 0208, this is called the kanji set, which includes 6355 kanji as well as 524 non-kanji, including characters such as Latin letters, kana, and so forth.
;Special characters
;Numerals
;Latin letters
;Hiragana
;Katakana
;Greek letters
;Cyrillic letters
;Box-drawing characters
;Kanji

Special characters, numerals, and Latin characters

As for the special characters in the kanji set, some characters from the graphic character set of the International Reference Version of ISO/IEC 646:1991 are absent from JIS X 0208. There are the aforementioned four characters "QUOTATION MARK", "APOSTROPHE", "HYPHEN-MINUS", and "TILDE". The former three are split into different code points in the kanji set. The "TILDE" of IRV has no corresponding character in the kanji set.
In the following table, the ISO/IEC 646:1991 IRV characters in question are compared with their multiple equivalents in JIS X 0208, except for the IRV character "TILDE", which is compared with the "WAVE DASH" of JIS X 0208. The entries under the "Symbol" columns utilize UCS/Unicode code points, so the specifics of display may differ.
The ASCII/IRV characters without exact JIS X 0208 equivalents were later assigned code points by JIS X 0213, these are also listed below, as are Microsoft's mapping of the four characters.
This means that the kanji set is the most widespread non-upward-compatible character set in the world; it is counted as one of the weak points of this standard.
Even with the 90 special characters, numerals, and Latin letters the kanji set and the IRV set have in common, this standard does not follow the arrangement of ISO/IEC 646. These 90 characters are split between rows 1 and 3, although row 3 does follow ISO 646 arrangement for the 62 letters and numbers alone in ISO 646 becomes 2/3 4/1.
As to the cause of how these numerals, Latin letters, and so forth in the kanji set are the "full-width alphanumeric characters" and how the original implementation came forth with a differing interpretation compared to the IRV, it is thought that it is due to these incompatibilities.
Ever since the first standard, it has been possible to represent composites such as encircled numbers, ligatures for measurement unit names, and Roman numerals; they were not given independent kuten code points. Although individual companies that manufacture information systems can make an effort to represent these characters as customers may require by the composition of the characters, none has requested to have them added to the standard, instead choosing to proprietarily offer them as gaiji.
In the fourth standard, all these characters were explicitly defined as characters that accompany an advancement of the current position; that is to say, they are spacing characters. Furthermore, it was ruled that they should not be made by the composition of characters. For this reason, it became disallowed to represent Latin characters with diacritics at all, with possibly the sole exception of the ångström symbol at row 2 cell 82.

Hiragana and katakana

The hiragana and katakana in JIS X 0208, unlike JIS X 0201, includes dakuten and handakuten markings as part of a character. The katakana and as well as the small, not in JIS X 0201, are also included.
The arrangement of kana in JIS X 0208 is different from the arrangement of katakana in JIS X 0201. In JIS X 0201, the syllabary starts with, followed by the small kana sorted by gojūon order, followed by the full-size kana, also in gojūon order. On the other hand, in JIS X 0208, the kana are sorted first by gojūon order, then in the order of "small kana, full-size kana, kana with dakuten, and kana with handakuten" such that the same fundamental kana is grouped with its derivatives. This ordering was chosen in order to more simply facilitate the sorting of kana-based dictionary look-ups.
As mentioned above, in this standard, the previously defined katakana order in JIS X 0201 was not followed in JIS X 0208. It is thought that the JIS X 0201 katakana being "half-width kana" arose due to the incompatibility with the katakana of this standard. This point is also one of the weaknesses of this standard.

Kanji

How the kanji in this standard were chosen from what sources, why they are split into level 1 and level 2, and how they are arranged are all explained in detail in the fourth standard. Per that explanation, the kanji included in the following four kanji listings were reflected in the 6349 characters of the first standard.
In the second and third standards, they added four and two characters to level 2, respectively, bringing the total kanji to 6355. Also, in the second standard, character forms were changed as well as transposition among the levels; in the third standard as well, character forms were changed. These are described further below.

Level partitioning

The 2,965 Level 1 kanji occupy rows 16 to 47. The 3,390 Level 2 kanji occupy rows 48 to 84.
For level 1, characters common to multiple kanji glyph listings were chosen, using the tōyō kanji, the tōyō kanji correction draft, and the jinmeiyō kanji as a basis. Also, JIS C 6260 and JIS C 6261 were consulted; kanji for nearly all Japanese prefectures, cities, districts, wards, towns, villages, and so forth were intentionally placed in level 1. Furthermore, amendments by experts were added.
Level 2 was dedicated to kanji that made an appearance in the aforementioned four major listings but were not selected for level 1. As noted below, the kanji of level 1 were ordered by their pronunciation, so among the kanji whose pronunciation were difficult to determine, there were those that were transferred from level 1 to level 2 on that basis.
Due to these decisions, for the most part, level 1 contains more frequently used kanji, and level 2 contains more infrequently used kanji, but of course, those were judged by the standards of the day; over the passage of time, some level 2 kanji have become more frequently used, such as one meaning "to soar" and one meaning "to glitter" ; and inversely, some level 1 kanji have become infrequent, notably the ones meaning "centimeter" and "millimeter". Also, a few jinmeiyō kanji, being added after the kanji set was defined, fall into level 2.

Arrangement

The kanji in level 1 are sorted in order of each one's "representative reading" ; the reading of a kanji for this may be an on or a kun reading; readings are sorted in gojūon order. As a general rule, the on reading is considered the representative reading; where a kanji has multiple on readings, the reading judged to be predominant in use frequency is used for the representative reading. For the small percentage of kanji that either do not have an on reading or have an on reading which is little known and not in common use, the kun reading was employed as the representative reading. Where a verb kun reading must be used as the representative reading, the form is used.
For example, cells 1 to 41 on row 16 are 41 characters sorted as starting with a reading of a. Within these, 22 characters, including 16-10 and 16-32 are there on the basis of their kun readings. 16-09 and 16-23 are just two examples of ren'yōkei-form verbs used for the representative reading.
Where the representative reading is the same between different kanji, a kanji that uses an on reading is placed ahead of one that uses a kun reading. Where the on or kun readings are the same between more than one kanji, they are then ordered by their primary radical and stroke count.
Whether on level 1 or level 2, itaiji are arranged to directly follow their exemplar form. For example, in level 2, right after row 49 cell 88, the immediately following characters deviate from the general rule to include three variants of 49-88.
The kanji in level 2 are arranged in order of primary radical and stroke count. Where these two properties are the same for different kanji, they are then sorted by reading.

Kanji from unknown sources

It has been pointed out that there are kanji in the kanji set that are not found in comprehensive, unabridged kanji dictionaries, and that the sources thereof are unknown. For example, only one year after the first standard was established, Tajima reported that he had confirmed 63 kanji that were not to be found in Shinjigen, nor in Dai Kan-Wa jiten, and they did not make sense as ryakuji of any sort; he noted that it would be preferable for kanji not available in kanji dictionaries to be selected from definite sources. These kanji came to be known as "ghost" characters or "ghost kanji", among other names.
The drafting committee for the fourth version of the standard also saw the existence of kanji with sources unknown as a problem, and so made an inquiry into just what kind of sources the drafting committee of the first version referenced. As a result, it was discovered that the original drafting committee had heavily relied on the "Correspondence Analysis Results" to collect kanji. When the drafting committee investigated the "Correspondence Analysis Results", it became clear that many of the kanji included in the kanji set but not found in exhaustive kanji dictionaries supposedly came from the "Japanese Personality Registration Name Kanji" and "Kanji for National Administrative District Listing" lists mentioned in the "Correspondence Analysis Results".
It was confirmed that no original text for the "Japanese Personality Registration Name Kanji" referenced in the "Correspondence Analysis Results" exists. For the "National Administrative District Listing", Sasahara Hiroyuki of the fourth version's drafting committee examined the kanji that appeared on the in-progress development pages for the first standard. The committee also consulted many ancient writings, as well as many examples of personal names in a database of NTT phone books.
Due to this thorough investigation, the committee was able to pare down the number of kanji for which the source cannot be confidently explained to twelve, shown on the adjacent table. Of these, it is conjectured that several glyphs came about due to copying errors. In particular, 妛 was probably created when printers tried to create ? by cutting and pasting 山 and 女 together. A shadow from that process was misinterpreted as a line, resulting in 妛.

Unification of kanji variants

According to the specifications in the fourth standard, unification is the action of giving the same code point to a character without regard to its different character forms. In the fourth standard, the glyphs allowed are limited; the extent to which particular allographic glyphs are unified into a graphemic code point is clearly defined.
Furthermore, according to the specifications in the standard, a glyph is an abstract notion as to the graphical representation of a graphic character; a character form is the representation as a graphical shape that a glyph takes in actuality. For a single glyph, there exist an endless range of possible concretely and/or visibly different character forms. A variation between a character form of one glyph is termed a "design difference".
The extent to which a glyph is unified to one code point is determined according to that code point's "example glyph" and the "unification criteria" that can be applied to that example glyph; that is, the example glyph for a code point applies to that code point, and any glyphs for which the parts that compose the example glyph are replaced in accordance with the unification criteria also apply to that code point.
For example, the example glyph at 33-46 is composed of radical 9 and the kanji that eventually spawned the both the so kana. Also, in unification criterion 101, there are three kanji displayed: the first takes the form most often seen in Japanese ; the second contains a more traditional form in which the first two strokes form radical 12 ; and the third is like the second, except that radical 12 is inverted. Consequently, all three permutations all apply to the code point at line 33 cell 46.
In the fourth standard, including one of the errata for the first printing, there are 186 unification criteria.
When a code point's example glyph is composed of more than one part glyph, unification criteria can be applied to each part. After a unification criterion is applied to one part glyph, that part cannot have any more unification criteria applied to it. Also, a unification criterion is not allowed to apply if the resulting glyph would coincide with that of another code point entirely.
An example glyph is no more than an example for that code point; it is not a glyph "endorsed" by the standard. Also, the unification criteria need only be used for generally used kanji and for the purpose of assigning things to the code points of this standard. The standard requests that generally unused kanji not be created based on the example glyphs and unification criteria.
The kanji of the kanji set are not chosen completely consistently according to the unification criteria. For example, although 41-7 corresponds to the form where the third and fourth strokes cross as well as the form where they don't according to unification criterion 72, 20-73 only corresponds to the form where they do not cross, and 80-90 only corresponds to the form where they do.
The terms "unification", "unification criteria", and "example glyph" were adopted in the fourth standard. From the first to the third version, kanji and relations between kanji were grouped into three types: "independent", "compatible", and "equivalent"; it was explained that the characters recognized as equivalent "consolidate to just one point". "Equivalence" included, other than kanji with exactly the same shape, kanji with differences due to style, and kanji where the difference in character form is small.
In the first standard, it was stipulated that "this standard... does not establish the particulars of character forms" ; it also states that "the aim of this standard is to establish the general idea of characters and their codes; the design of their character forms and such lie outside its scope." In the second and third standards as well, notes to the effect that specific designs of character forms lie outside its scope. The fourth standard also stipulates that "This standard regulates graphic characters as well as their bit patterns, and the use, specific designs of individual characters, and so forth are not within the scope of this standard".

Unification criteria for compatibility

In the fourth standard, "unification criteria for maintaining compatibility with previous standards" is defined. Their application is limited to 29 code points whose glyphs vary greatly between the standards JIS C 6226-1983 on and after and JIS C 6226-1978. For those 29 code points, the glyphs from JIS C 6226-1983 on and after are displayed as "A", and the glyphs from JIS C 6226-1978 as "B". On each of them, both "A" and "B" glyphs may be applied. However, in order to claim compatibility with the standard, whether the "A" or "B" form has been used for each code point must be explicitly noted.

Character encodings

Encoding schemes stipulated by JIS X 0208

In JIS X 0208:1997, article 7 combined with appendices 1 and 2 define a total of eight encoding schemes.
In the descriptions below, the "CL", "GL", "CR", and "GR" regions are respectively, in column/line notation, from 0/0 to 1/15, from 2/1 to 7/14, from 8/0 to 9/15, and from 10/1 to 15/14. For each code, 2/0 is assigned the graphic character "SPACE" and 7/15 the control character "DELETE". The C0 control characters are assigned to the CL region.
;7-bit encoding for kanji
;8-bit encoding for kanji
;International Reference Version + 7-bit encoding for kanji
;Latin characters + 7-bit encoding for kanji
;International Reference Version + 8-bit encoding for kanji
;Latin characters + 8-bit encoding for kanji
;Shift-coded character set
;RFC 1468-coded character set
Among the encodings stipulated in the fourth standard, only the "Shift" coded character set is registered by the IANA. However, certain others are closely related to IANA-registered encodings defined elsewhere.

Escape sequences for JIS X 0202 / ISO 2022

JIS X 0208 may be used within ISO 2022/JIS X 0202. The escape sequences to designate JIS X 0208 to each of the four ISO 2022 code sets are listed below. Here, "ESC" refers to the control character "Escape".
StandardG0G1G2G3
78ESC 2/4 4/0ESC 2/4 2/9 4/0ESC 2/4 2/10 4/0ESC 2/4 2/11 4/0
83ESC 2/4 4/2ESC 2/4 2/9 4/2ESC 2/4 2/10 4/2ESC 2/4 2/11 4/2
90 onwardESC 2/6 4/0 ESC 2/4 4/2ESC 2/6 4/0 ESC 2/4 2/9 4/2ESC 2/6 4/0 ESC 2/4 2/10 4/2ESC 2/6 4/0 ESC 2/4 2/11 4/2

The escape sequence starting ESC 2/4 selects a multi-byte character set. The escape sequence starting ESC 2/6 specifies a revision of the upcoming character set selection. JIS C 6226:1978 is identified by the multibyte-94-set identifier byte 4/0. JIS C 6226:1983 / JIS X 0208:1983 is identified by the multibyte-94-set identifier byte 4/2. JIS X 0208:1990 is also identified by the 94-set identifier byte 4/2, but can be distinguished with the revision identifier 4/0.

Duplicate encodings of ASCII and JIS X 0201

When using the kanji set of this standard with either the ISO/IEC 646:1991 IRV graphic character set or JIS X 0201's graphic character set for Latin characters, the treatment of the characters common to both sets becomes problematic. Unless one takes special measures, the characters included in both sets do not all map to each other one-to-one, and a single character may be given more than one code point; that is, it may cause a duplicate encoding.
JIS X 0208:1997, in regards to when a character is common to both sets, basically forbids the use of the code point in the kanji set, eliminating duplicate encodings. It is judged that characters that have the same name are the same character.
For example, both the name of the character corresponding to the bit pattern 4/1 in ASCII and the name of the character corresponding to row 3 cell 33 of the kanji set are "LATIN CAPITAL LETTER A". In International Reference Version + 8-bit code for kanji, whether by the bit pattern 4/1 or by the bit pattern corresponding to the kanji set's row 3 cell 33, the letter "A" is represented. The standard forbids the use of the "10/3 12/1" bit pattern, in an attempt to eliminate the duplicate encoding.
In consideration to implementations that treat the characters of the code points in the kanji set as "full-width characters" and those of ASCII or JIS-Roman as different characters, the use of the kanji set code points is permitted only for the sake of backwards compatibility. For example, for the purpose of backwards compatibility, it is permitted to consider 10/3 12/1 in International Reference Version + 8-bit code for kanji to correspond to a full-width "A".
If the kanji set is used along with ASCII or JIS-Roman, then even if the standard is abided by strictly, the unique encoding of a character is not guaranteed. For example, in the International Reference Version + 8-bit code for kanji, it is valid to represent a hyphen with the bit pattern 2/13 for the character "HYPHEN-MINUS", as well as with the kanji set's row 1 cell 30 for the character "HYPHEN". In addition, the standard does not define which of the two to use for what, and so the hyphen is not given one unique encoding. The same problem affects the minus sign, the quotation marks, and so forth.
Moreover, even if the kanji set is used as a separate code, there is no guarantee that the unique encoding of characters is implemented. In many cases, however, the full-width "IDEOGRAPHIC SPACE" at row 1 cell 1 and the half-width space coexist. How the two should be different is not self-explanatory, and is not specified in the standard.

Comparison of encoding schemes used in practice

History

Until five years have passed after a Japanese Industrial Standard has been established, reaffirmed, or revised, the prior standard undergoes a process of reaffirmation, revision, or withdrawal. Since establishment, the standard has been subject to revision three times, and at present, the fourth standard is valid.

First standard

The first standard is JIS C 6226-1978 "Code of Japanese Graphic Character Set for Information Interchange", established by the Japanese Minister of International Trade and Industry on 1 January 1978. It is also called 78JIS for short. Entrusted by the Agency of Industrial Science and Technology, a JIPDEC kanji code standardization research and study committee produced the draft. The committee chairman was Moriguchi Shigeichi.
The code included 453 non-Kanji and 6349 Kanji for a total of 6802 characters. It did not yet include box-drawing characters. The standard itself was set in Shaken Co., Ltd's Ishii Mincho typeface.

Second standard

The second standard JIS C 6226-1983 "Code of Japanese Graphic Character Set for Information Interchange" revised the first standard on 1 September 1983. It is also called 83JIS. Entrusted by the AIST, a JIPDEC kanji code-related JIS committee produced the draft. The committee chairman was Motooka Tōru.
The draft of the second standard was based on the consideration of factors such as the promulgation of the jōyō kanji, the enforcement of the jinmeiyō kanji, and the standardization of Japanese-language Teletex by the Ministry of Posts and Telecommunications; also, the next modification was performed to keep pace with JIS C 6234-1983.
;Addition of special characters
;Newly added box-drawing characters
;Swapping of itaiji code points
;Additions to the level 2 kanji
;Modification of character forms
Among the changes in those 300 or so kanji character forms, many level 1 glyphs that were in the style of the Kangxi Dictionary were changed into variants, and especially more simplified forms. For example, a couple of code points that are often the subject of criticism due to being greatly changed are row 18 cell 10 and row 38 cell 34.
There were many smaller changes away from the Kangxi-style variants; for example, row 25 cell 84 lost part of a stroke. Also, where some glyphs for level 1 kanji were not Kangxi-style forms, there were some changed into their Kangxi-style forms; for example, row 80 cell 49 gained part of a stroke.
In order to elucidate the original intent of the first standard, these ended up falling into parameters for unification criteria in the fourth standard. The difference in form for the examples noted above falls under the parameters for unification criterion 42.
The bulk of the changes to character forms are differences between level 1 and level 2 kanji. Specifically, simplification was done more often for level 1 kanji than for level 2 kanji; simplifications applied to level 1 kanji were not generally applied to kanji in level 2. The aforementioned 25-84 and 80-49 were given different treatment likewise, as the former is in level 1 and the latter is in level 2. Even so, there were some changes regardless of the level; for instance characters containing the "door" and "winter" components were changed with no different treatment between level 1 and level 2 kanji.
However, for 29 code points, the forms inherited by the fourth standard contradicts the original intent of the first. For these, there are special unification criteria to maintain compatibility with the previous standards at these code points.
When the new "X" category for Japanese Industrial Standards was introduced, the second standard was re-termed JIS X 0208-1983 on 1 March 1987.

Third standard

The third standard JIS X 0208-1990 "Code of Japanese Graphic Character Set for Information Interchange" revised the second standard on 1 September 1990. It is also called 90JIS for short. Entrusted by the AIST, a committee at the Japanese Standards Association for the revision of JIS X 0208 created the draft. The committee chairman was Tajima Kazuo.
225 kanji glyphs were changed, and two characters were added to level 2. This was a disunification of itaiji for two characters already included. Some of the changes and the two additions corresponded to the 118 jinmeiyō kanji added in March 1990. The standard itself was set in Heisei Mincho.

Fourth standard

The fourth standard JIS X 0208:1997 "7-bit and 8-bit double byte coded KANJI sets for information interchange" revised the third standard on 20 January 1997. It is also called 97JIS for short. Entrusted by the AIST, a JSA committee for research and study of coded character sets produced the draft. The committee chairman was Shibano Kōji.
The basic policies of this revision were to perform no changes the character set, to clarify ambiguous provisions, and to make the standard relatively easier to use. Addition, removal, and code point rearrangement were not done, and without exception, the example glyphs were also left unchanged. However, the stipulations of the standard were completely re-written and/or supplemented. Whereas the third standard was 65 pages long without the explanations, the fourth standard was 374 pages without the explanations.
The main points of the revision are:
;Definition of encoding methods
;Definition of the general prohibition of the use of unassigned code points and methods of usage for unassigned code points
;General elimination of duplicate encodings
;Investigation into sources of kanji
;Definition of kanji unification criteria
;Inclusion of de facto standards

Successors

was designed "with the goal being to offer a sufficient character set for the purposes of encoding the modern Japanese language that JIS X 0208 intended to be from the start"; it defines a character set that expands upon the kanji set of JIS X 0208. The drafters of JIS X 0213 recommend migration from JIS X 0208 to JIS X 0213, among the advantages being JIS X 0213's compatibility with the Hyōgai Kanji Glyph List and with newer jinmeiyō kanji.
Contrary to the expectations of the drafters, adoption of JIS X 0213 has been anything but fast since its enactment in the year 2000. The drafting committee of JIS X 0213:2004 wrote, "The status where 'what the majority of information systems can use in common is JIS X 0208 only' still continues."
For Microsoft Windows, the predominant operating system in the personal computing sector, the JIS X 0213 repertoire has been included since Windows Vista, released in November 2006. Mac OS X has been compatible with JIS X 0213 since version 10.1. Many Unix-likes such as Linux can support JIS X 0213 if desired. Therefore, it is thought that with time, JIS X 0213 support on personal computers will not be an impediment to its eventual adoption.
Among the drafters of JIS X 0213, there are those who expect to see a mix of JIS X 0208 and JIS X 0213 before any adoption of JIS X 0213. However, JIS X 0208 continues to be used for the present, and many predict it to endure as a standard. There are barriers that need to be overcome if JIS X 0213 is to supplant JIS X 0208 in common usage:
Because JIS X 0208 / JIS C 6226 is primarily a character set and not a strictly defined character encoding, several companies have implemented their own encodings of the character set.
Several of these incorporate vendor-specific character assignments in place of unallocated regions of the standard. These include Windows-932 and MacJapanese, as well as NEC's PC98 character encoding. While IBM-932 and IBM-942 also include vendor assignments, they include them outside of the region used for JIS X 0208.

Relation to other standards

ISO/IEC 646 IRV and ASCII

As noted above, the kanji set is not upwardly compatible with the ISO/IEC 646:1991 IRV graphic character set. The kanji set and the IRV graphic character set can be used together as specified in JIS X 0208. They can be used together in EUC-JP as well.

JIS X 0201

The kanji set lacks three characters included in JIS X 0201's graphic character set for Latin characters: 2/2, 2/7, and 2/13. The kanji set contains all character included in JIS X 0201's graphic character set for katakana.
The kanji set and the graphic character set for Latin characters can be used together as specified in JIS X 0208. The kanji set, graphic character set for Latin characters, and JIS X 0201's graphic character set for katakana can be used together as specified in JIS X 0208. The kanji set and graphic character set for katakana can be used together in EUC-JP.

JIS X 0212

defines additional characters with code points for the purposes of information processing that requires characters not found in JIS X 0208. Rather than allocating characters within the main JIS X 0208 kanji set, it defines a second 94-by-94 kanji set containing supplementary characters.
JIS X 0212 can be used with JIS X 0208 in EUC-JP. Also, JIS X 0208 and JIS X 0212 are both source standards for UCS/Unicode's Han unification, meaning that kanji from both sets can be included in one Unicode-format document.
Among the code points that the second version of JIS X 0208 changed, 28 code points in JIS X 0212 reflect the character forms from before the changes. Also, JIS X 0212 reassigns the "closure mark" that JIS X 0208 had assigned as a non-kanji as a kanji. JIS X 0212 has no characters in common with JIS X 0208 other than these. Hence, it is not suited for general use on its own.
However, in the fourth version of JIS X 0208, the connection to JIS X 0212 was not defined at all. It is believed that this is because the drafting committee of the fourth JIS X 0208 standard had a critical opinion of the selection and identification methods of JIS X 0212. The character meanings and selection rationales were not properly documented, making it difficult to identify whether desired kanji corresponded to those in its repertoire. The text of the fourth standard, as well as pointing out the problematic points of the character selection of JIS X 0212, states that "it is thought that not only is character selection impossible, it is also impossible to use together; the connection to JIS X 0212 is not defined at all."

JIS X 0213

defines a kanji set that expands upon the kanji set of JIS X 0208. According to this standard, it is "designed with the goal being to offer a sufficient character set for the purposes of encoding the modern Japanese language that JIS X 0208 intended to be from the start."
The kanji set of JIS X 0213 incorporates all characters that can be represented in the kanji set of JIS X 0208, with many additions. In total, JIS X 0213 defines 1183 non-kanji and 10,050 kanji, within two 94-by-94 planes. The first plane is based on JIS X 0208, whereas the second plane is designed to fit within the unallocated rows of JIS X 0212, allowing use in EUC-JP. JIS X 0213 also defines Shift_JISx0213, a variant of Shift_JIS capable of encoding the entirety of JIS X 0213.
For most intents and purposes, JIS X 0213 plane 1 is a superset of JIS X 0208. However, different unification criteria are applied to some code points in JIS X 0213 compared to JIS X 0208. Consequently, some pairs of kanji glyphs that were represented by one JIS X 0208 code point, due to being unified, are given separate code points in JIS X 0213. For example, the glyph at row 33 cell 46 of JIS X 0208 unifies a few variants due to its right-hand component. In JIS X 0213, two forms are unified on plane 1 row 33 cell 46, and the other is located at plane 1 row 14 cell 41. Therefore, whether JIS X 0208 row 33 cell 46 should be mapped to JIS X 0213 plane 1 row 33 cell 46 or plane 1 row 14 cell 41 cannot be determined automatically. This limits the extent to which JIS X 0213 can be considered upwardly compatible with JIS X 0208, as admitted by the JIS X 0213 drafting committee.
However, for the most part, row m cell n in JIS X 0208 corresponds to plane 1 row m cell n in JIS X 0213; therefore, not much confusion arises in practice. This is because most typefaces have come to use the glyphs exemplified in JIS X 0208, and most users are not consciously aware of the unification criteria.

ISO/IEC 10646 and Unicode

The kanji set of JIS X 0208 is among the original source standards for the Han unification in ISO/IEC 10646 and Unicode. Every kanji in JIS X 0208 corresponds to its own code point in UCS/Unicode's Basic Multilingual Plane.
The non-kanji in JIS X 0208 also correspond to their own code points in the BMP. However, for some special characters, some systems implement a different correspondences from those of UCS/Unicode's.

Footnotes

Explanatory