Six-bit character code: Difference between revisions

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{{Short description|Computer encoding of characters}}

{{Use dmy dates|date=May 2019|cs1-dates=y}}

A '''six-bit character code''' is a [[character encoding]] designed for use on computers with [[word length]]s a multiple of 6. Six bits can only encode 64 distinct characters, so these codes generally include only the upper-case letters, the numerals, some punctuation characters, and sometimes control characters. The [[IBM 7 track|7-track]] [[Magnetic -tape data storage|magnetic tape]] format was developed to store data in such codes, along with an additional [[parity bit]].

==Types of six-bit codes==

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The TTS code had two pairs of shift codes allowing a total of four shift states. The first operated much like a keyboard's shift key and selected between a lower-case and digits repertoire, and an upper-case and symbols one. A second pair of Linotype-specific "lower rail" and "upper rail" shift codes would select an alternate (usually italic) font.

===BCD six-bit codecodes===

Six-bit [[BCD (6-bitcharacter encoding)|BCD]] code wascodes thewere adaptationadaptations of the [[punched card code]] to [[binary code]]. [[IBM]] applied the terms ''binary-coded decimal'' and ''BCD'' to the variations of BCD ''alphamerics'' used in most early IBM computers, including the [[IBM 1620]], [[IBM 1400 series]], and non-[[IBM 700/7000 series#Decimal architecture (7070/7072/7074)|decimal architecture]] members of the [[IBM 700/7000 series]].

===COBOL databases six-bit code===

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===DEC SIXBIT code<span class="anchor" id="DEC six-bit code"></span>===

A popular six-bit code was [[Digital Equipment Corporation|DEC]] SIXBIT. This is simply the ASCII character codes from 32 to 95 coded as 0 to 63 by subtracting 32 (i.e., columns 2, 3, 4, and 5 of the ASCII table (16 characters to a column), shifted to columns 0 through 3, by subtracting 2 from the high bits); it includes the space, punctuation characters, numbers, and capital letters, but no control characters. Since it included no control characters, not even end-of-line, it was not used for general text processing. However, six-character names such as [[filename]]s and [[assembly language|assembler]] [[identifier|symbol]]s could be stored in a single [[36-bit]] word of the [[PDP-10]], and three characters fit in each word of the [[PDP-1]] and two characters fit in each word of the [[PDP-8]]. See [[#ASCII-variants|table below]].

Another, less common, variant is obtained by just stripping the high bit of an ASCII code in 32 - 95 range (codes 32 - 63 remain at their positions, higher values have 64 subtracted from them). Such variant was sometimes used on DEC's [[PDP-8]] (1965).

==={{anchor|ECMA-1}}ECMA and ISO six-bit code===

A six-bit code similar to DEC's, but replacing a few punctuation characters with the most useful control characters&mdash;including [[Shift Out and Shift In characters|SO/SI]], allowing code extension&mdash;was specified as [[Ecma International|ECMA]]-[https://ecma-international.org/publications-and-standards/standards/ecma-1/ 1] in 1963 (see [[#ASCII-variants|below]]). Four years later, ISO Recommendation R 646-1967 (which later evolved into [[ISO/IEC_646 | ISO Standard 646]]) included an almost identical six-bit code, differing only in some of the alternative options permitted for a few characters. ECMA-1 was eventually withdrawn, and ISO 646-1973 explicitly removed the six-bit code leaving only 7-bit ASCII.

===FIELDATA six-bit code===

[[FIELDATA]] was a seven-bit code (with optional parity) of which only 64 code positions (occupying six bits) were formally defined.<ref name="Mackenzie_1980">{{cite book |url=https://textfiles.meulie.net/bitsaved/Books/Mackenzie_CodedCharSets.pdf |title=Coded Character Sets, History and Development |series=The Systems Programming Series |author-last=Mackenzie |author-first=Charles E. |date=1980 |edition=1 |publisher=[[Addison-Wesley Publishing Company, Inc.]] |isbn=978-0-201-14460-4 |lccn=77-90165 |access-date=2019-08-25 |archive-url=https://web.archive.org/web/20160526172151/https://textfiles.meulie.net/bitsaved/Books/Mackenzie_CodedCharSets.pdf |archive-date=May 26, 2016 |url-status=live |df=mdy-all }}</ref> A variant was used by [[UNIVAC]]'s 1100-series computers.<ref name="Walker_1996">{{cite web |title=UNIVAC 1100 Series FIELDATA Code |work=UNIVAC Memories |author-first=John |author-last=Walker |date=1996-08-06 |url=https://www.fourmilab.ch/documents/univac/fieldata.html |access-date=2016-05-22 |url-status=live |archive-url=https://web.archive.org/web/20160522120813/https://www.fourmilab.ch/documents/univac/fieldata.html |archive-date=2016-05-22}}</ref> Treating the code as a six-bit code these systems used a 36-bit word (capable of storing six such reduced FIELDATA characters).<ref name="Jennings_2016">{{cite web |title=An annotated history of some character codes or ASCII: American Standard Code for Information Infiltration |at=FIELDATA |author-first=Thomas Daniel |author-last=Jennings |author-link=Tom Jennings |website=sensitive research (SR-IX) |date=2016-04-20 |orig-year=1999 |url=https://www.sr-ix.com/Archive/CharCodeHist/index.html#FIELDATA |access-date=2022-06-01}}</ref>

===Braille six-bit code===

[[Braille]] characters are represented using six dot positions, arranged in a rectangle. Each position may contain a raised dot or not, so Braille can be considered to be a six-bit binary code. Some more modern Braille systems add an extra two dots, making these systems an eight-bit code instead.

==Six-bit codes for binary-to-text encoding==

{{See also|Binary-to-text encoding}}

Transmission of binary data over systems which are designed for text only can sometimes introduce problems. For example, [[email]] historically supported only 7-bit ASCII codes and would strip the 8th bit, thus corrupting binary data sent directly through any troublesome mail server. Other systems can cause issues by improperly interpreting control characters during storage or transmission.

A number of schemes exist to pack 8-bit data into text-only representations which can pass through text mail systems, to be decoded at the destination. Examples of 6-bit character subsets used for packing binary data include [[Uuencode]] and [[Base64]]. These sets contain no control characters (only printable numbers, letters, some punctuation, and maybe space) and allow data to be transmitted over any medium which is also able to transmit human-readable text.

=={{anchor|BCD-variants}}Examples of BCD six-bit codes==

IBM, which dominated commercial data processing use a variety of six-bit codes, which were tied to the character set used on [[punched card]]s, ''see'' [[BCD (character encoding)]].

Other vendor character codes are shown below, with their [[Unicode]] equivalents.

{|{{Chset-table-header1|CDC 1604: Magnetic tape BCD codes}}

|-

|{{chset-left1|0x}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-cell1|U+0031 DIGIT ONE|[[1]]}}

|{{chset-cell1|U+0032 DIGIT TWO|[[2]]}}

|{{chset-cell1|U+0033 DIGIT THREE|[[3]]}}

|{{chset-cell1|U+0034 DIGIT FOUR|[[4]]}}

|{{chset-cell1|U+0035 DIGIT FIVE|[[5]]}}

|{{chset-cell1|U+0036 DIGIT SIX|[[6]]}}

|{{chset-cell1|U+0037 DIGIT SEVEN|[[7]]}}

|{{chset-cell1|U+0038 DIGIT EIGHT|[[8]]}}

|{{chset-cell1|U+0039 DIGIT NINE|[[9]]}}

|{{chset-cell1|U+0030 DIGIT ZERO|[[0]]}}

|{{chset-cell1|U+0023 NUMBER SIGN|[[number sign|#]]}}

|{{chset-cell1|U+0040 COMMERCIAL AT|[[@]]}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-ctrl1|TAPE MARK|[[End-of-file|TAPE<br/>MARK]]|style=line-height:1}}

|-

|{{chset-left1|1x}}

|{{chset-ctrl1|U+0020 SPACE|&nbsp;{{Control code link|SP}}&nbsp;}}

|{{chset-cell1|U+002F SOLIDUS|[[Slash (punctuation)|/]]}}

|{{chset-cell1|U+0053 LATIN CAPITAL LETTER S|[[S]]}}

|{{chset-cell1|U+0054 LATIN CAPITAL LETTER T|[[T]]}}

|{{chset-cell1|U+0055 LATIN CAPITAL LETTER U|[[U]]}}

|{{chset-cell1|U+0056 LATIN CAPITAL LETTER V|[[V]]}}

|{{chset-cell1|U+0057 LATIN CAPITAL LETTER W|[[W]]}}

|{{chset-cell1|U+0058 LATIN CAPITAL LETTER X|[[X]]}}

|{{chset-cell1|U+0059 LATIN CAPITAL LETTER Y|[[Y]]}}

|{{chset-cell1|U+005A LATIN CAPITAL LETTER Z|[[Z]]}}

|{{chset-ctrl1|RECORD MARK|[[BCD (character encoding)#Recordmark character|REC<br/>MARK]]|style=line-height:1}}

|{{chset-cell1|U+002C COMMA|[[,]]}}

|{{chset-cell1|U+0025 PERCENT SIGN|[[%]]}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-cell1|||style=background:#DDD}}

|-

|{{chset-left1|2x}}

|{{chset-cell1|U+002D HYPHEN-MINUS|[[Hyphen-minus|-]]}}

|{{chset-cell1|U+004A LATIN CAPITAL LETTER J|[[J]]}}

|{{chset-cell1|U+004B LATIN CAPITAL LETTER K|[[K]]}}

|{{chset-cell1|U+004C LATIN CAPITAL LETTER L|[[L]]}}

|{{chset-cell1|U+004D LATIN CAPITAL LETTER M|[[M]]}}

|{{chset-cell1|U+004E LATIN CAPITAL LETTER N|[[N]]}}

|{{chset-cell1|U+004F LATIN CAPITAL LETTER O|[[O]]}}

|{{chset-cell1|U+0050 LATIN CAPITAL LETTER P|[[P]]}}

|{{chset-cell1|U+0051 LATIN CAPITAL LETTER Q|[[Q]]}}

|{{chset-cell1|U+0052 LATIN CAPITAL LETTER R|[[R]]}}

|{{chset-cell1|U+002D HYPHEN-MINUS U+0030 DIGIT ZERO|[[-0]]}}

|{{chset-cell1|U+0024 DOLLAR SIGN|[[$]]}}

|{{chset-cell1|U+002A ASTERISK|[[Asterisk|*]]}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-cell1|||style=background:#DDD}}

|-

|{{chset-left1|3x}}

|{{chset-cell1|U+0026 AMPERSAND|[[ampersand|&]]}}

|{{chset-cell1|U+0041 LATIN CAPITAL LETTER A|[[A]]}}

|{{chset-cell1|U+0042 LATIN CAPITAL LETTER B|[[B]]}}

|{{chset-cell1|U+0043 LATIN CAPITAL LETTER C|[[C]]}}

|{{chset-cell1|U+0044 LATIN CAPITAL LETTER D|[[D]]}}

|{{chset-cell1|U+0045 LATIN CAPITAL LETTER E|[[E]]}}

|{{chset-cell1|U+0046 LATIN CAPITAL LETTER F|[[F]]}}

|{{chset-cell1|U+0047 LATIN CAPITAL LETTER G|[[G]]}}

|{{chset-cell1|U+0048 LATIN CAPITAL LETTER H|[[H]]}}

|{{chset-cell1|U+0049 LATIN CAPITAL LETTER I|[[I]]}}

|{{chset-cell1|U+002B PLUS SIGN U+0030 DIGIT ZERO|[[+0]]}}

|{{chset-cell1|U+002E FULL STOP|[[full stop|.]]}}

|{{chset-cell1|U+00A4 CURRENCY SIGN|[[¤]]}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-ctrl1|GROUP MARK|[[BCD (character encoding)#Groupmark character|GRP<br/>MARK]]|style=line-height:1}}

|}

{|{{Chset-table-header1|CDC 1604: [[Punched card]] codes}}

|-

|{{chset-left1|0x}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-cell1|U+0031 DIGIT ONE|[[1]]}}

|{{chset-cell1|U+0032 DIGIT TWO|[[2]]}}

|{{chset-cell1|U+0033 DIGIT THREE|[[3]]}}

|{{chset-cell1|U+0034 DIGIT FOUR|[[4]]}}

|{{chset-cell1|U+0035 DIGIT FIVE|[[5]]}}

|{{chset-cell1|U+0036 DIGIT SIX|[[6]]}}

|{{chset-cell1|U+0037 DIGIT SEVEN|[[7]]}}

|{{chset-cell1|U+0038 DIGIT EIGHT|[[8]]}}

|{{chset-cell1|U+0039 DIGIT NINE|[[9]]}}

|{{chset-cell1|U+0030 DIGIT ZERO|[[0]]}}

|{{chset-cell1|U+003D EQUALS SIGN|[[equals sign|{{=}}]]}}

|{{chset-cell1|U+2212 MINUS SIGN|[[−]]}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-cell1|||style=background:#DDD}}

|-

|{{chset-left1|1x}}

|{{chset-ctrl1|U+0020 SPACE|&nbsp;{{Control code link|SP}}&nbsp;}}

|{{chset-cell1|U+002F SOLIDUS|[[Slash (punctuation)|/]]}}

|{{chset-cell1|U+0053 LATIN CAPITAL LETTER S|[[S]]}}

|{{chset-cell1|U+0054 LATIN CAPITAL LETTER T|[[T]]}}

|{{chset-cell1|U+0055 LATIN CAPITAL LETTER U|[[U]]}}

|{{chset-cell1|U+0056 LATIN CAPITAL LETTER V|[[V]]}}

|{{chset-cell1|U+0057 LATIN CAPITAL LETTER W|[[W]]}}

|{{chset-cell1|U+0058 LATIN CAPITAL LETTER X|[[X]]}}

|{{chset-cell1|U+0059 LATIN CAPITAL LETTER Y|[[Y]]}}

|{{chset-cell1|U+005A LATIN CAPITAL LETTER Z|[[Z]]}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-cell1|U+002C COMMA|[[,]]}}

|{{chset-cell1|U+0028 LEFT PARENTHESIS|[[Parenthesis|(]]}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-cell1|||style=background:#DDD}}

|-

|{{chset-left1|2x}}

|{{chset-cell1|U+2014 EM DASH|[[—]]}}

|{{chset-cell1|U+004A LATIN CAPITAL LETTER J|[[J]]}}

|{{chset-cell1|U+004B LATIN CAPITAL LETTER K|[[K]]}}

|{{chset-cell1|U+004C LATIN CAPITAL LETTER L|[[L]]}}

|{{chset-cell1|U+004D LATIN CAPITAL LETTER M|[[M]]}}

|{{chset-cell1|U+004E LATIN CAPITAL LETTER N|[[N]]}}

|{{chset-cell1|U+004F LATIN CAPITAL LETTER O|[[O]]}}

|{{chset-cell1|U+0050 LATIN CAPITAL LETTER P|[[P]]}}

|{{chset-cell1|U+0051 LATIN CAPITAL LETTER Q|[[Q]]}}

|{{chset-cell1|U+0052 LATIN CAPITAL LETTER R|[[R]]}}

|{{chset-cell1|U+002D HYPHEN-MINUS U+0030 DIGIT ZERO|[[-0]]}}

|{{chset-cell1|U+0024 DOLLAR SIGN|[[$]]}}

|{{chset-cell1|U+002A ASTERISK|[[Asterisk|*]]}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-cell1|||style=background:#DDD}}

|-

|{{chset-left1|3x}}

|{{chset-cell1|U+002B PLUS SIGN|[[Plus sign|+]]}}

|{{chset-cell1|U+0041 LATIN CAPITAL LETTER A|[[A]]}}

|{{chset-cell1|U+0042 LATIN CAPITAL LETTER B|[[B]]}}

|{{chset-cell1|U+0043 LATIN CAPITAL LETTER C|[[C]]}}

|{{chset-cell1|U+0044 LATIN CAPITAL LETTER D|[[D]]}}

|{{chset-cell1|U+0045 LATIN CAPITAL LETTER E|[[E]]}}

|{{chset-cell1|U+0046 LATIN CAPITAL LETTER F|[[F]]}}

|{{chset-cell1|U+0047 LATIN CAPITAL LETTER G|[[G]]}}

|{{chset-cell1|U+0048 LATIN CAPITAL LETTER H|[[H]]}}

|{{chset-cell1|U+0049 LATIN CAPITAL LETTER I|[[I]]}}

|{{chset-cell1|U+002B PLUS SIGN U+0030 DIGIT ZERO|[[+0]]}}

|{{chset-cell1|U+002E FULL STOP|[[full stop|.]]}}

|{{chset-cell1|U+0029 RIGHT PARENTHESIS|[[Parenthesis|)]]}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-cell1|||style=background:#DDD}}

|}

{|{{Chset-table-header1|CDC 1612: Printer codes (business applications)}}

|-

|{{chset-left1|0x}}

|{{chset-cell1|U+003A COLON|[[colon (punctuation)|&#x3A;]]}}

|{{chset-cell1|U+0031 DIGIT ONE|[[1]]}}

|{{chset-cell1|U+0032 DIGIT TWO|[[2]]}}

|{{chset-cell1|U+0033 DIGIT THREE|[[3]]}}

|{{chset-cell1|U+0034 DIGIT FOUR|[[4]]}}

|{{chset-cell1|U+0035 DIGIT FIVE|[[5]]}}

|{{chset-cell1|U+0036 DIGIT SIX|[[6]]}}

|{{chset-cell1|U+0037 DIGIT SEVEN|[[7]]}}

|{{chset-cell1|U+0038 DIGIT EIGHT|[[8]]}}

|{{chset-cell1|U+0039 DIGIT NINE|[[9]]}}

|{{chset-cell1|U+0030 DIGIT ZERO|[[0]]}}

|{{chset-cell1|U+003D EQUALS SIGN|[[equals sign|{{=}}]]}}

|{{chset-cell1|U+2260 NOT EQUAL TO|[[≠]]}}

|{{chset-cell1|U+2264 LESS-THAN OR EQUAL TO|[[Inequality (mathematics)|≤]]}}

|{{chset-cell1|U+0021 EXCLAMATION MARK|[[Exclamation mark|!]]}}

|{{chset-cell1|U+005B LEFT SQUARE BRACKET|[[Square brackets|&#91;]]}}

|-

|{{chset-left1|1x}}

|{{chset-ctrl1|U+0020 SPACE|&nbsp;{{Control code link|SP}}&nbsp;}}

|{{chset-cell1|U+002F SOLIDUS|[[Slash (punctuation)|/]]}}

|{{chset-cell1|U+0053 LATIN CAPITAL LETTER S|[[S]]}}

|{{chset-cell1|U+0054 LATIN CAPITAL LETTER T|[[T]]}}

|{{chset-cell1|U+0055 LATIN CAPITAL LETTER U|[[U]]}}

|{{chset-cell1|U+0056 LATIN CAPITAL LETTER V|[[V]]}}

|{{chset-cell1|U+0057 LATIN CAPITAL LETTER W|[[W]]}}

|{{chset-cell1|U+0058 LATIN CAPITAL LETTER X|[[X]]}}

|{{chset-cell1|U+0059 LATIN CAPITAL LETTER Y|[[Y]]}}

|{{chset-cell1|U+005A LATIN CAPITAL LETTER Z|[[Z]]}}

|{{chset-cell1|U+005D RIGHT SQUARE BRACKET|[[Square brackets|&#93;]]}}

|{{chset-cell1|U+002C COMMA|[[,]]}}

|{{chset-cell1|U+0028 LEFT PARENTHESIS|[[Parenthesis|(]]}}

|{{chset-cell1|U+2192 RIGHTWARDS ARROW|[[Arrow (symbol)|→]]}}

|{{chset-cell1|U+2261 IDENTICAL TO|[[List of mathematical symbols|≡]]}}

|{{chset-cell1|U+007E TILDE|[[Tilde|~]]}}

|-

|{{chset-left1|2x}}

|{{chset-cell1|U+2212 MINUS SIGN|[[−]]}}

|{{chset-cell1|U+004A LATIN CAPITAL LETTER J|[[J]]}}

|{{chset-cell1|U+004B LATIN CAPITAL LETTER K|[[K]]}}

|{{chset-cell1|U+004C LATIN CAPITAL LETTER L|[[L]]}}

|{{chset-cell1|U+004D LATIN CAPITAL LETTER M|[[M]]}}

|{{chset-cell1|U+004E LATIN CAPITAL LETTER N|[[N]]}}

|{{chset-cell1|U+004F LATIN CAPITAL LETTER O|[[O]]}}

|{{chset-cell1|U+0050 LATIN CAPITAL LETTER P|[[P]]}}

|{{chset-cell1|U+0051 LATIN CAPITAL LETTER Q|[[Q]]}}

|{{chset-cell1|U+0052 LATIN CAPITAL LETTER R|[[R]]}}

|{{chset-cell1|U+0025 PERCENT SIGN|[[Percent sign|%]]}}

|{{chset-cell1|U+0024 DOLLAR SIGN|[[$]]}}

|{{chset-cell1|U+002A ASTERISK|[[Asterisk|*]]}}

|{{chset-cell1|U+2191 UPWARDS ARROW|[[Arrow (symbol)|↑]]}}

|{{chset-cell1|U+2193 DOWNWARDS ARROW|[[Arrow (symbol)|↓]]}}

|{{chset-cell1|U+003E GREATER-THAN SIGN|[[greater-than sign|&gt;]]}}

|-

|{{chset-left1|3x}}

|{{chset-cell1|U+002B PLUS SIGN|[[Plus sign|+]]}}

|{{chset-cell1|U+0041 LATIN CAPITAL LETTER A|[[A]]}}

|{{chset-cell1|U+0042 LATIN CAPITAL LETTER B|[[B]]}}

|{{chset-cell1|U+0043 LATIN CAPITAL LETTER C|[[C]]}}

|{{chset-cell1|U+0044 LATIN CAPITAL LETTER D|[[D]]}}

|{{chset-cell1|U+0045 LATIN CAPITAL LETTER E|[[E]]}}

|{{chset-cell1|U+0046 LATIN CAPITAL LETTER F|[[F]]}}

|{{chset-cell1|U+0047 LATIN CAPITAL LETTER G|[[G]]}}

|{{chset-cell1|U+0048 LATIN CAPITAL LETTER H|[[H]]}}

|{{chset-cell1|U+0049 LATIN CAPITAL LETTER I|[[I]]}}

|{{chset-cell1|U+003C LESS-THAN SIGN|[[less-than sign|&lt;]]}}

|{{chset-cell1|U+002E FULL STOP|[[full stop|.]]}}

|{{chset-cell1|U+0029 RIGHT PARENTHESIS|[[Parenthesis|)]]}}

|{{chset-cell1|U+2265 GREATER-THAN OR EQUAL TO|[[≥]]}}

|{{chset-cell1|U+003F QUESTION MARK|[[question mark|?]]}}

|{{chset-cell1|U+003B SEMICOLON|[[semicolon|&#x3B;]]}}

|}

=={{anchor|ASCII-variants}}Examples of six-bit ASCII variants==

{|{{chset-table-header1|DEC SIXBIT}}

|-

Line 352 ⟶ 106:

|{{chset-cell1|U+005F LOW LINE|[[Underscore|_]]}}

|}

==={{anchor|ECMA-1}}ECMA and ISO six-bit code===

A six-bit code similar to DEC's, but replacing a few punctuation characters with the most useful control characters&mdash;including [[Shift Out and Shift In characters|SO/SI]], allowing code extension&mdash;was specified as [[Ecma International|ECMA]]-[https://ecma-international.org/publications-and-standards/standards/ecma-1/ 1] in 1963. Four years later, ISO Recommendation R 646-1967 (which later evolved into [[ISO/IEC_646 | ISO Standard 646]]) included an almost identical six-bit code, differing only in some of the alternative options permitted for a few characters. ECMA-1 was eventually withdrawn, and ISO 646-1973 explicitly removed the six-bit code, standardizing only its 7-bit code.

{|{{chset-table-header1|ECMA-1 and ISO/R 646:1967}}

Line 389 ⟶ 146:

|{{chset-cell1|U+003D EQUALS SIGN / U+0025 PERCENT|[[equals sign|{{=}}]]/[[percent sign|%]]}}

|{{chset-cell1|U+003E GREATER-THAN SIGN / U+0026 AMPERSAND|[[greater-than sign|&gt;]]/[[ampersand|&amp;]]}}

|{{chset-cell1|U+003F QUESTION MARK/ U+0027 APOSTROPHE|[[question mark|?]]/[[apostrophe|']]|fn={{efn|name=iso646q}}}}

|-

|{{chset-left1|2x}}

Line 429 ⟶ 186:

{{notelist|refs=

{{efn|name=crlf|In systems where LF both advances to the next line and returns the carriage to the start position, CR may instead be used as a "spare control" according to ECMA-1, and as BS "backspace" according to ISO/R 646. LF then has the designation NL "new line".}}

{{efn|name=natopt|These characterscharacter positions are intended for nationalizationnational use. Where the local alphabet contains letters additional to the basic latin alphabet, they should be assigned to these character positions. The default assignments, according to ECMA-1, are listed here.}}

{{efn|name=iso646q|ECMA-1 permits either the question mark or the apostrophe in this position. ISO/R 646 permits the apostrophe only, making it an invariant.}}

}}

===ICT/ICL 6-bit character set===

The [[ICT_1900_series#Character_sets|ICT (later ICL) 1900-series]] of mainframes<!--any others??--> used a six-bit code derived from an early 1963 version of [[ASCII]] for internal storage and processing, referred to as the "ECMA character set" in its documentation.

{|{{chset-table-header1|ICL Mainframes}}

Line 507 ⟶ 268:

|}

===AIS SixBit ASCII===

{|{{chset-table-header1|SixBit ASCII (used by [[Automatic identification system|AIS]])<ref name='Raymond'>{{cite web |url=https://gpsd.gitlab.io/gpsd/AIVDM.html#_ais_payload_data_types |title=AIVDM/AIVDO protocol decoding |at=AIS Payload Data Types |access-date=2024-03-14 |author-last=Raymond |author-first=Eric S. |date=2023-06-24}}</ref>}}

The [[automatic identification system]] (AIS) uses this code.<ref name='Raymond'>{{cite web |url=https://gpsd.gitlab.io/gpsd/AIVDM.html#_ais_payload_data_types |title=AIVDM/AIVDO protocol decoding |at=AIS Payload Data Types |access-date=2024-03-14 |author-last=Raymond |author-first=Eric S. |date=2023-06-24}}</ref>

{|{{chset-table-header1|AIS SixBit ASCII}}

|-

|{{chset-left1|0x}}

Line 580 ⟶ 343:

|{{chset-cell1|U+003E GREATER-THAN SIGN|[[greater-than sign|&gt;]]}}

|{{chset-cell1|U+003F QUESTION MARK|[[question mark|?]]}}

|}

===FIELDATA six-bit code===

[[FIELDATA]] was a seven-bit code (with optional parity) of which only 64 code positions (occupying six bits) were formally defined.<ref name="Mackenzie_1980">{{cite book |url=https://textfiles.meulie.net/bitsaved/Books/Mackenzie_CodedCharSets.pdf |title=Coded Character Sets, History and Development |series=The Systems Programming Series |author-last=Mackenzie |author-first=Charles E. |date=1980 |edition=1 |publisher=[[Addison-Wesley Publishing Company, Inc.]] |isbn=978-0-201-14460-4 |lccn=77-90165 |access-date=2019-08-25 |archive-url=https://web.archive.org/web/20160526172151/https://textfiles.meulie.net/bitsaved/Books/Mackenzie_CodedCharSets.pdf |archive-date=May 26, 2016 |url-status=live |df=mdy-all }}</ref> A variant was used by [[UNIVAC]]'s 1100-series computers.<ref name="Walker_1996">{{cite web |title=UNIVAC 1100 Series FIELDATA Code |work=UNIVAC Memories |author-first=John |author-last=Walker |date=1996-08-06 |url=https://www.fourmilab.ch/documents/univac/fieldata.html |access-date=2016-05-22 |url-status=live |archive-url=https://web.archive.org/web/20160522120813/https://www.fourmilab.ch/documents/univac/fieldata.html |archive-date=2016-05-22}}</ref> Treating the code as a six-bit code these systems used a 36-bit word (capable of storing six such reduced FIELDATA characters).<ref name="Jennings_2016">{{cite web |title=An annotated history of some character codes or ASCII: American Standard Code for Information Infiltration |at=FIELDATA |author-first=Thomas Daniel |author-last=Jennings |author-link=Tom Jennings |website=sensitive research (SR-IX) |date=2016-04-20 |orig-year=1999 |url=https://www.sr-ix.com/Archive/CharCodeHist/index.html#FIELDATA |access-date=2022-06-01}}</ref>

===Braille six-bit code===

[[Braille]] characters are represented using six dot positions, arranged in a rectangle. Each position may contain a raised dot or not, so Braille can be considered to be a six-bit binary code. Some more modern Braille systems add an extra two dots, making these systems an eight-bit code instead.

==Six-bit codes for binary-to-text encoding==

{{See also|Binary-to-text encoding}}

Transmission of binary data over systems which are designed for text only can sometimes introduce problems. For example, [[email]] historically supported only 7-bit ASCII codes and would strip the 8th bit, thus corrupting binary data sent directly through any troublesome mail server. Other systems can cause issues by improperly interpreting control characters during storage or transmission.

A number of schemes exist to pack 8-bit data into text-only representations which can pass through text mail systems, to be decoded at the destination. Examples of 6-bit character subsets used for packing binary data include [[Uuencode]] and [[Base64]]. These sets contain no control characters (only printable numbers, letters, some punctuation, and maybe space) and allow data to be transmitted over any medium which is also able to transmit human-readable text.

=={{anchor|BCD-variants}}Examples of BCD six-bit codes==

IBM, which dominated commercial data processing use a variety of six-bit codes, which were tied to the character set used on [[punched card]]s, ''see'' [[BCD (character encoding)]].

Other vendor character codes are shown below, with their [[Unicode]] equivalents.

{|{{Chset-table-header1|CDC 1604: Magnetic tape BCD codes}}

|-

|{{chset-left1|0x}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-cell1|U+0031 DIGIT ONE|[[1]]}}

|{{chset-cell1|U+0032 DIGIT TWO|[[2]]}}

|{{chset-cell1|U+0033 DIGIT THREE|[[3]]}}

|{{chset-cell1|U+0034 DIGIT FOUR|[[4]]}}

|{{chset-cell1|U+0035 DIGIT FIVE|[[5]]}}

|{{chset-cell1|U+0036 DIGIT SIX|[[6]]}}

|{{chset-cell1|U+0037 DIGIT SEVEN|[[7]]}}

|{{chset-cell1|U+0038 DIGIT EIGHT|[[8]]}}

|{{chset-cell1|U+0039 DIGIT NINE|[[9]]}}

|{{chset-cell1|U+0030 DIGIT ZERO|[[0]]}}

|{{chset-cell1|U+0023 NUMBER SIGN|[[number sign|#]]}}

|{{chset-cell1|U+0040 COMMERCIAL AT|[[@]]}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-ctrl1|TAPE MARK|[[End-of-file|TAPE<br/>MARK]]|style=line-height:1}}

|-

|{{chset-left1|1x}}

|{{chset-ctrl1|U+0020 SPACE|&nbsp;{{Control code link|SP}}&nbsp;}}

|{{chset-cell1|U+002F SOLIDUS|[[Slash (punctuation)|/]]}}

|{{chset-cell1|U+0053 LATIN CAPITAL LETTER S|[[S]]}}

|{{chset-cell1|U+0054 LATIN CAPITAL LETTER T|[[T]]}}

|{{chset-cell1|U+0055 LATIN CAPITAL LETTER U|[[U]]}}

|{{chset-cell1|U+0056 LATIN CAPITAL LETTER V|[[V]]}}

|{{chset-cell1|U+0057 LATIN CAPITAL LETTER W|[[W]]}}

|{{chset-cell1|U+0058 LATIN CAPITAL LETTER X|[[X]]}}

|{{chset-cell1|U+0059 LATIN CAPITAL LETTER Y|[[Y]]}}

|{{chset-cell1|U+005A LATIN CAPITAL LETTER Z|[[Z]]}}

|{{chset-ctrl1|RECORD MARK|[[BCD (character encoding)#Recordmark character|REC<br/>MARK]]|style=line-height:1}}

|{{chset-cell1|U+002C COMMA|[[,]]}}

|{{chset-cell1|U+0025 PERCENT SIGN|[[%]]}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-cell1|||style=background:#DDD}}

|-

|{{chset-left1|2x}}

|{{chset-cell1|U+002D HYPHEN-MINUS|[[Hyphen-minus|-]]}}

|{{chset-cell1|U+004A LATIN CAPITAL LETTER J|[[J]]}}

|{{chset-cell1|U+004B LATIN CAPITAL LETTER K|[[K]]}}

|{{chset-cell1|U+004C LATIN CAPITAL LETTER L|[[L]]}}

|{{chset-cell1|U+004D LATIN CAPITAL LETTER M|[[M]]}}

|{{chset-cell1|U+004E LATIN CAPITAL LETTER N|[[N]]}}

|{{chset-cell1|U+004F LATIN CAPITAL LETTER O|[[O]]}}

|{{chset-cell1|U+0050 LATIN CAPITAL LETTER P|[[P]]}}

|{{chset-cell1|U+0051 LATIN CAPITAL LETTER Q|[[Q]]}}

|{{chset-cell1|U+0052 LATIN CAPITAL LETTER R|[[R]]}}

|{{chset-cell1|U+002D HYPHEN-MINUS U+0030 DIGIT ZERO|[[-0]]}}

|{{chset-cell1|U+0024 DOLLAR SIGN|[[$]]}}

|{{chset-cell1|U+002A ASTERISK|[[Asterisk|*]]}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-cell1|||style=background:#DDD}}

|-

|{{chset-left1|3x}}

|{{chset-cell1|U+0026 AMPERSAND|[[ampersand|&]]}}

|{{chset-cell1|U+0041 LATIN CAPITAL LETTER A|[[A]]}}

|{{chset-cell1|U+0042 LATIN CAPITAL LETTER B|[[B]]}}

|{{chset-cell1|U+0043 LATIN CAPITAL LETTER C|[[C]]}}

|{{chset-cell1|U+0044 LATIN CAPITAL LETTER D|[[D]]}}

|{{chset-cell1|U+0045 LATIN CAPITAL LETTER E|[[E]]}}

|{{chset-cell1|U+0046 LATIN CAPITAL LETTER F|[[F]]}}

|{{chset-cell1|U+0047 LATIN CAPITAL LETTER G|[[G]]}}

|{{chset-cell1|U+0048 LATIN CAPITAL LETTER H|[[H]]}}

|{{chset-cell1|U+0049 LATIN CAPITAL LETTER I|[[I]]}}

|{{chset-cell1|U+002B PLUS SIGN U+0030 DIGIT ZERO|[[+0]]}}

|{{chset-cell1|U+002E FULL STOP|[[full stop|.]]}}

|{{chset-cell1|U+00A4 CURRENCY SIGN|[[¤]]}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-ctrl1|GROUP MARK|[[BCD (character encoding)#Groupmark character|GRP<br/>MARK]]|style=line-height:1}}

|}

{|{{Chset-table-header1|CDC 1604: [[Punched card]] codes}}

|-

|{{chset-left1|0x}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-cell1|U+0031 DIGIT ONE|[[1]]}}

|{{chset-cell1|U+0032 DIGIT TWO|[[2]]}}

|{{chset-cell1|U+0033 DIGIT THREE|[[3]]}}

|{{chset-cell1|U+0034 DIGIT FOUR|[[4]]}}

|{{chset-cell1|U+0035 DIGIT FIVE|[[5]]}}

|{{chset-cell1|U+0036 DIGIT SIX|[[6]]}}

|{{chset-cell1|U+0037 DIGIT SEVEN|[[7]]}}

|{{chset-cell1|U+0038 DIGIT EIGHT|[[8]]}}

|{{chset-cell1|U+0039 DIGIT NINE|[[9]]}}

|{{chset-cell1|U+0030 DIGIT ZERO|[[0]]}}

|{{chset-cell1|U+003D EQUALS SIGN|[[equals sign|{{=}}]]}}

|{{chset-cell1|U+2212 MINUS SIGN|[[−]]}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-cell1|||style=background:#DDD}}

|-

|{{chset-left1|1x}}

|{{chset-ctrl1|U+0020 SPACE|&nbsp;{{Control code link|SP}}&nbsp;}}

|{{chset-cell1|U+002F SOLIDUS|[[Slash (punctuation)|/]]}}

|{{chset-cell1|U+0053 LATIN CAPITAL LETTER S|[[S]]}}

|{{chset-cell1|U+0054 LATIN CAPITAL LETTER T|[[T]]}}

|{{chset-cell1|U+0055 LATIN CAPITAL LETTER U|[[U]]}}

|{{chset-cell1|U+0056 LATIN CAPITAL LETTER V|[[V]]}}

|{{chset-cell1|U+0057 LATIN CAPITAL LETTER W|[[W]]}}

|{{chset-cell1|U+0058 LATIN CAPITAL LETTER X|[[X]]}}

|{{chset-cell1|U+0059 LATIN CAPITAL LETTER Y|[[Y]]}}

|{{chset-cell1|U+005A LATIN CAPITAL LETTER Z|[[Z]]}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-cell1|U+002C COMMA|[[,]]}}

|{{chset-cell1|U+0028 LEFT PARENTHESIS|[[Parenthesis|(]]}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-cell1|||style=background:#DDD}}

|-

|{{chset-left1|2x}}

|{{chset-cell1|U+2014 EM DASH|[[—]]}}

|{{chset-cell1|U+004A LATIN CAPITAL LETTER J|[[J]]}}

|{{chset-cell1|U+004B LATIN CAPITAL LETTER K|[[K]]}}

|{{chset-cell1|U+004C LATIN CAPITAL LETTER L|[[L]]}}

|{{chset-cell1|U+004D LATIN CAPITAL LETTER M|[[M]]}}

|{{chset-cell1|U+004E LATIN CAPITAL LETTER N|[[N]]}}

|{{chset-cell1|U+004F LATIN CAPITAL LETTER O|[[O]]}}

|{{chset-cell1|U+0050 LATIN CAPITAL LETTER P|[[P]]}}

|{{chset-cell1|U+0051 LATIN CAPITAL LETTER Q|[[Q]]}}

|{{chset-cell1|U+0052 LATIN CAPITAL LETTER R|[[R]]}}

|{{chset-cell1|U+002D HYPHEN-MINUS U+0030 DIGIT ZERO|[[-0]]}}

|{{chset-cell1|U+0024 DOLLAR SIGN|[[$]]}}

|{{chset-cell1|U+002A ASTERISK|[[Asterisk|*]]}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-cell1|||style=background:#DDD}}

|-

|{{chset-left1|3x}}

|{{chset-cell1|U+002B PLUS SIGN|[[Plus sign|+]]}}

|{{chset-cell1|U+0041 LATIN CAPITAL LETTER A|[[A]]}}

|{{chset-cell1|U+0042 LATIN CAPITAL LETTER B|[[B]]}}

|{{chset-cell1|U+0043 LATIN CAPITAL LETTER C|[[C]]}}

|{{chset-cell1|U+0044 LATIN CAPITAL LETTER D|[[D]]}}

|{{chset-cell1|U+0045 LATIN CAPITAL LETTER E|[[E]]}}

|{{chset-cell1|U+0046 LATIN CAPITAL LETTER F|[[F]]}}

|{{chset-cell1|U+0047 LATIN CAPITAL LETTER G|[[G]]}}

|{{chset-cell1|U+0048 LATIN CAPITAL LETTER H|[[H]]}}

|{{chset-cell1|U+0049 LATIN CAPITAL LETTER I|[[I]]}}

|{{chset-cell1|U+002B PLUS SIGN U+0030 DIGIT ZERO|[[+0]]}}

|{{chset-cell1|U+002E FULL STOP|[[full stop|.]]}}

|{{chset-cell1|U+0029 RIGHT PARENTHESIS|[[Parenthesis|)]]}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-cell1|||style=background:#DDD}}

|{{chset-cell1|||style=background:#DDD}}

|}

{|{{Chset-table-header1|CDC 1612: Printer codes (business applications)}}

|-

|{{chset-left1|0x}}

|{{chset-cell1|U+003A COLON|[[colon (punctuation)|&#x3A;]]}}

|{{chset-cell1|U+0031 DIGIT ONE|[[1]]}}

|{{chset-cell1|U+0032 DIGIT TWO|[[2]]}}

|{{chset-cell1|U+0033 DIGIT THREE|[[3]]}}

|{{chset-cell1|U+0034 DIGIT FOUR|[[4]]}}

|{{chset-cell1|U+0035 DIGIT FIVE|[[5]]}}

|{{chset-cell1|U+0036 DIGIT SIX|[[6]]}}

|{{chset-cell1|U+0037 DIGIT SEVEN|[[7]]}}

|{{chset-cell1|U+0038 DIGIT EIGHT|[[8]]}}

|{{chset-cell1|U+0039 DIGIT NINE|[[9]]}}

|{{chset-cell1|U+0030 DIGIT ZERO|[[0]]}}

|{{chset-cell1|U+003D EQUALS SIGN|[[equals sign|{{=}}]]}}

|{{chset-cell1|U+2260 NOT EQUAL TO|[[≠]]}}

|{{chset-cell1|U+2264 LESS-THAN OR EQUAL TO|[[Inequality (mathematics)|≤]]}}

|{{chset-cell1|U+0021 EXCLAMATION MARK|[[Exclamation mark|!]]}}

|{{chset-cell1|U+005B LEFT SQUARE BRACKET|[[Square brackets|&#91;]]}}

|-

|{{chset-left1|1x}}

|{{chset-ctrl1|U+0020 SPACE|&nbsp;{{Control code link|SP}}&nbsp;}}

|{{chset-cell1|U+002F SOLIDUS|[[Slash (punctuation)|/]]}}

|{{chset-cell1|U+0053 LATIN CAPITAL LETTER S|[[S]]}}

|{{chset-cell1|U+0054 LATIN CAPITAL LETTER T|[[T]]}}

|{{chset-cell1|U+0055 LATIN CAPITAL LETTER U|[[U]]}}

|{{chset-cell1|U+0056 LATIN CAPITAL LETTER V|[[V]]}}

|{{chset-cell1|U+0057 LATIN CAPITAL LETTER W|[[W]]}}

|{{chset-cell1|U+0058 LATIN CAPITAL LETTER X|[[X]]}}

|{{chset-cell1|U+0059 LATIN CAPITAL LETTER Y|[[Y]]}}

|{{chset-cell1|U+005A LATIN CAPITAL LETTER Z|[[Z]]}}

|{{chset-cell1|U+005D RIGHT SQUARE BRACKET|[[Square brackets|&#93;]]}}

|{{chset-cell1|U+002C COMMA|[[,]]}}

|{{chset-cell1|U+0028 LEFT PARENTHESIS|[[Parenthesis|(]]}}

|{{chset-cell1|U+2192 RIGHTWARDS ARROW|[[Arrow (symbol)|→]]}}

|{{chset-cell1|U+2261 IDENTICAL TO|[[List of mathematical symbols|≡]]}}

|{{chset-cell1|U+007E TILDE|[[Tilde|~]]}}

|-

|{{chset-left1|2x}}

|{{chset-cell1|U+2212 MINUS SIGN|[[−]]}}

|{{chset-cell1|U+004A LATIN CAPITAL LETTER J|[[J]]}}

|{{chset-cell1|U+004B LATIN CAPITAL LETTER K|[[K]]}}

|{{chset-cell1|U+004C LATIN CAPITAL LETTER L|[[L]]}}

|{{chset-cell1|U+004D LATIN CAPITAL LETTER M|[[M]]}}

|{{chset-cell1|U+004E LATIN CAPITAL LETTER N|[[N]]}}

|{{chset-cell1|U+004F LATIN CAPITAL LETTER O|[[O]]}}

|{{chset-cell1|U+0050 LATIN CAPITAL LETTER P|[[P]]}}

|{{chset-cell1|U+0051 LATIN CAPITAL LETTER Q|[[Q]]}}

|{{chset-cell1|U+0052 LATIN CAPITAL LETTER R|[[R]]}}

|{{chset-cell1|U+0025 PERCENT SIGN|[[Percent sign|%]]}}

|{{chset-cell1|U+0024 DOLLAR SIGN|[[$]]}}

|{{chset-cell1|U+002A ASTERISK|[[Asterisk|*]]}}

|{{chset-cell1|U+2191 UPWARDS ARROW|[[Arrow (symbol)|↑]]}}

|{{chset-cell1|U+2193 DOWNWARDS ARROW|[[Arrow (symbol)|↓]]}}

|{{chset-cell1|U+003E GREATER-THAN SIGN|[[greater-than sign|&gt;]]}}

|-

|{{chset-left1|3x}}

|{{chset-cell1|U+002B PLUS SIGN|[[Plus sign|+]]}}

|{{chset-cell1|U+0041 LATIN CAPITAL LETTER A|[[A]]}}

|{{chset-cell1|U+0042 LATIN CAPITAL LETTER B|[[B]]}}

|{{chset-cell1|U+0043 LATIN CAPITAL LETTER C|[[C]]}}

|{{chset-cell1|U+0044 LATIN CAPITAL LETTER D|[[D]]}}

|{{chset-cell1|U+0045 LATIN CAPITAL LETTER E|[[E]]}}

|{{chset-cell1|U+0046 LATIN CAPITAL LETTER F|[[F]]}}

|{{chset-cell1|U+0047 LATIN CAPITAL LETTER G|[[G]]}}

|{{chset-cell1|U+0048 LATIN CAPITAL LETTER H|[[H]]}}

|{{chset-cell1|U+0049 LATIN CAPITAL LETTER I|[[I]]}}

|{{chset-cell1|U+003C LESS-THAN SIGN|[[less-than sign|&lt;]]}}

|{{chset-cell1|U+002E FULL STOP|[[full stop|.]]}}

|{{chset-cell1|U+0029 RIGHT PARENTHESIS|[[Parenthesis|)]]}}

|{{chset-cell1|U+2265 GREATER-THAN OR EQUAL TO|[[≥]]}}

|{{chset-cell1|U+003F QUESTION MARK|[[question mark|?]]}}

|{{chset-cell1|U+003B SEMICOLON|[[semicolon|&#x3B;]]}}

|}