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A six-bit character code is a character encoding designed for use on computers with word lengths 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 7-track magnetic tape format was developed to store data in such codes, along with an additional parity bit.

Types of six-bit codes

An early six-bit binary code was used for Braille, the reading system for the blind that was developed in the 1820s.

The earliest computers dealt with numeric data only, and made no provision for character data. Six-bit BCD, with several variants, was used by IBM on early computers such as the IBM 702 in 1953 and the IBM 704 in 1954. Six-bit encodings were replaced by the 8-bit EBCDIC code starting in 1964, when System/360 standardized on 8-bit bytes. There are some variants of this type of code (see below).

Six-bit character codes generally succeeded the five-bit Baudot code and preceded seven-bit ASCII.

Six-bit codes could encode more than 64 characters by the use of Shift Out and Shift In characters, essentially incorporating two distinct 62-character sets and switching between them. For example, the popular IBM 2741 communications terminal supported a variety of character sets of up to 88 printing characters plus control characters.

Teletypesetter code

A special 6-level extension of the 5-level International Telegraph Alphabet was used to remotely control Linotype machines beginning around 1930. By 1950 it was widely used by wire services to send preformatted news stories to participating newspapers. It supported the 90 printable characters characters of a Linotype machine, plus whitespace characters.

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 code

Six-bit BCD code was the adaptation 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-decimal architecture members of the IBM 700/7000 series.

COBOL databases six-bit code

A six-bit code was also used in COBOL databases, where end-of-record information was stored separately.

Magnetic stripe card six-bit code

A six-bit code, with added odd parity bit, is used on Track 1 of magnetic stripe cards, as specified in ISO/IEC 7811-2.

DEC SIXBIT code

A popular six-bit code was 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 filenames and assembler symbols 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 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).

ECMA six-bit code

A six-bit code similar to DEC's, but replacing a few punctuation characters with the most useful control characters—including SO/SI, allowing code extension—was specified as ECMA-1 in 1963 (see below).

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. A variant was used by UNIVAC's 1100-series computers. Treating the code as a six-bit code these systems used a 36-bit word (capable of storing six such reduced FIELDATA characters).

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

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.

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 cards, see BCD (character encoding).

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

Examples of six-bit ASCII variants

GOST 6-bit code

Example of six-bit Braille codes

The following table shows the arrangement of characters, with the hex value, corresponding ASCII character, Braille 6-bit codes (dot combinations), Braille Unicode glyph, and general meaning (the actual meaning may change depending on context).

Hex ASCII Glyph Braille Dots Braille Glyph Braille Meaning 20 (space) (space) 21 ! 2-3-4-6 the 22 " 5 (contraction) 23 # 3-4-5-6 (number prefix) 24 $ 1-2-4-6 ed 25 % 1-4-6 sh 26 & 1-2-3-4-6 and 27 ' 3 ' 28 ( 1-2-3-5-6 of 29 ) 2-3-4-5-6 with 2A * 1-6 ch 2B + 3-4-6 ing 2C , 6 (uppercase prefix) 2D - 3-6 - 2E . 4-6 (italic prefix) 2F / 3-4 st 30 0 3-5-6 " 31 1 2 , 32 2 2-3 ; 33 3 2-5 : 34 4 2-5-6 . 35 5 2-6 en 36 6 2-3-5 ! 37 7 2-3-5-6 ( or ) 38 8 2-3-6 " or ? 39 9 3-5 in 3A : 1-5-6 wh 3B ; 5-6 (letter prefix) 3C < 1-2-6 gh 3D = 1-2-3-4-5-6 for 3E > 3-4-5 ar 3F ? 1-4-5-6 th

Hex ASCII Glyph Braille Dots Braille Glyph Braille Meaning 40 @ 4 (accent prefix) 41 A 1 a 42 B 1-2 b 43 C 1-4 c 44 D 1-4-5 d 45 E 1-5 e 46 F 1-2-4 f 47 G 1-2-4-5 g 48 H 1-2-5 h 49 I 2-4 i 4A J 2-4-5 j 4B K 1-3 k 4C L 1-2-3 l 4D M 1-3-4 m 4E N 1-3-4-5 n 4F O 1-3-5 o 50 P 1-2-3-4 p 51 Q 1-2-3-4-5 q 52 R 1-2-3-5 r 53 S 2-3-4 s 54 T 2-3-4-5 t 55 U 1-3-6 u 56 V 1-2-3-6 v 57 W 2-4-5-6 w 58 X 1-3-4-6 x 59 Y 1-3-4-5-6 y 5A Z 1-3-5-6 z 5B [ 2-4-6 ow 5C \ 1-2-5-6 ou 5D ] 1-2-4-5-6 er 5E 4-5 (contraction) 5F _ 4-5-6 (contraction)

See also

• Binary-coded decimal
• BCD (character encoding)
• CDC display code
• DEC RADIX 50 / MOD40
• IBM SQUOZE
• IBM Transcode
• ASCII
• Baudot code
• EBCDIC
• Unicode
• ANSI X3.64
• UTF-8
• UTF-16
• Teletypesetter code (TTS)

References

1. IBM Corporation (1954). 704 electronic data-processing machine: manual of operation (PDF).
2. Mackenzie, Charles E. (1980). Coded Character Sets, History and Development (PDF). The Systems Programming Series (1 ed.). Addison-Wesley Publishing Company, Inc. ISBN 978-0-201-14460-4. LCCN 77-90165. Archived (PDF) from the original on May 26, 2016. Retrieved August 25, 2019.
3. Walker, John (1996-08-06). "UNIVAC 1100 Series FIELDATA Code". UNIVAC Memories. Archived from the original on 2016-05-22. Retrieved 2016-05-22.
4. Jennings, Thomas Daniel (2016-04-20) . "An annotated history of some character codes or ASCII: American Standard Code for Information Infiltration". sensitive research (SR-IX). FIELDATA. Retrieved 2022-06-01.
5. Raymond, Eric S. (2023-06-24). "AIVDM/AIVDO protocol decoding". AIS Payload Data Types. Retrieved 2024-03-14.
6. "Representing and Displaying Braille". DotlessBraille.org. 2002-02-20. Retrieved 2024-03-14.
7. Halleck, John (2000-08-24). "braille-ascii.ads". Braille.Ascii. Archived from the original on 2010-06-13. Retrieved 2009-08-10.

External links

• "Control Data 1604-C Computer Reference Manual" (PDF). (7.44 MB)
• "ECMA Standard for a 6 Bit Input/Output Character Code". (1.53 MB)
• SIXBIT Character Code Reference at the Wayback Machine (archived 2020-02-11) - Digital Equipment Corporation SIXBIT character coding system

v t e Character encodings
Early telecommunications	Telegraph code Needle Morse Non-Latin Wabun/Kana Chinese Cyrillic Baudot and Murray Fieldata ASCII ISO/IEC 646 BCDIC Teletex and Videotex/Teletext T.51/ISO/IEC 6937 ITU T.61 ITU T.101 World System Teletext background sets Transcode
ISO/IEC 8859	Approved parts -1 (Western Europe) -2 (Central Europe) -3 (Maltese/Esperanto) -4 (North Europe) -5 (Cyrillic) -6 (Arabic) -7 (Greek) -8 (Hebrew) -9 (Turkish) -10 (Nordic) -11 (Thai) -13 (Baltic) -14 (Celtic) -15 (New Western Europe) -16 (Romanian) Abandoned parts -12 (Devanagari) Proposed but not approved KOI-8 Cyrillic Sámi Adaptations Welsh Barents Cyrillic Estonian Ukrainian Cyrillic
Bibliographic use	MARC-8 ANSEL CCCII/EACC ISO 5426 5426-2 5427 5428 6438 6862
National standards	ArmSCII Big5 BraSCII CNS 11643 DIN 66003 ELOT 927 GOST 10859 GB 2312 GB 12345 GB 12052 GB 18030 HKSCS ISCII JIS X 0201 JIS X 0208 JIS X 0212 JIS X 0213 KOI-7 KPS 9566 KS X 1001 KS X 1002 LST 1564 LST 1590-4 PASCII Shift JIS SI 960 TIS-620 TSCII VISCII VSCII YUSCII
ISO/IEC 2022	ISO/IEC 8859 ISO/IEC 10367 Extended Unix Code / EUC
Mac OS Code pages ("scripts")	Armenian Arabic Barents Cyrillic Celtic Central European Croatian Cyrillic Devanagari Farsi (Persian) Font X (Kermit) Gaelic Georgian Greek Gujarati Gurmukhi Hebrew Iceland Inuit Keyboard Latin (Kermit) Maltese/Esperanto Ogham Roman Romanian Sámi Turkish Turkic Cyrillic Ukrainian VT100
DOS code pages	437 668 708 720 737 770 773 775 776 777 778 850 851 852 853 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 897 899 903 904 932 936 942 949 950 951 1040 1042 1043 1046 1098 1115 1116 1117 1118 1127 3846 ABICOMP CS Indic CSX Indic CSX+ Indic CWI-2 Iran System Kamenický Mazovia MIK
IBM AIX code pages	895 896 912 915 921 922 1006 1008 1009 1010 1012 1013 1014 1015 1016 1017 1018 1019 1046 1124 1133
Windows code pages	CER-GS 932 936 (GBK) 950 1169 Extended Latin-8 1250 1251 1252 1253 1254 1255 1256 1257 1258 1270 Cyrillic + Finnish Cyrillic + French Cyrillic + German Polytonic Greek
EBCDIC code pages	Japanese language in EBCDIC DKOI
DEC terminals (VTx)	Multinational (MCS) National Replacement (NRCS) French Canadian Swiss Spanish United Kingdom Dutch Finnish French Norwegian and Danish Swedish Norwegian and Danish (alternative) 8-bit Greek 8-bit Turkish SI 960 Hebrew Special Graphics Technical (TCS)
Platform specific	1052 1053 1054 1055 1056 1057 1058 Acorn RISC OS Amstrad CPC Apple II ATASCII Atari ST BICS Casio calculators CDC Compucolor 8001 Compucolor II CP/M+ DEC RADIX 50 DEC MCS/NRCS DG International Galaksija GEM GSM 03.38 HP Roman HP FOCAL HP RPL SQUOZE LICS LMBCS MSX NEC APC NeXT PETSCII PostScript Standard PostScript Latin 1 SAM Coupé Sega SC-3000 Sharp calculators Sharp MZ Sinclair QL Teletext TI calculators TRS-80 Ventura International WISCII XCCS ZX80 ZX81 ZX Spectrum
Unicode / ISO/IEC 10646	UTF-1 UTF-7 UTF-8 UTF-16 UTF-32 UTF-EBCDIC GB 18030 DIN 91379 BOCU-1 CESU-8 SCSU TACE16 Comparison of Unicode encodings
TeX typesetting system	Cork LY1 OML OMS OT1
Miscellaneous code pages	ABICOMP ASMO 449 Digital encoding of APL symbols ISO-IR-68 ARIB STD-B24 Fieldata HZ IEC-P27-1 INIS 7-bit 8-bit ISO-IR-169 ISO 2033 KOI KOI8-R KOI8-RU KOI8-U Mojikyō SEASCII Stanford/ITS Symbol TRON Unified Hangul Code
Control character	Morse prosigns C0 and C1 control codes ISO/IEC 6429 JIS X 0211 Unicode control, format and separator characters Whitespace characters
Related topics	CCSID Character encodings in HTML Charset detection Han unification Hardware code page MICR code Mojibake Variable-length encoding
Character sets

• Character encoding