Six-bit character code

Computer encoding of characters

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

[edit]

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.[1]: p.35 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

[edit]

Main articles: Teleprinter § Teletypesetter, and Telegraph code § TeleTypeSetter

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

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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

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

### Magnetic stripe card six-bit code

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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

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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

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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

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FIELDATA was a seven-bit code (with optional parity) of which only 64 code positions (occupying six bits) were formally defined.[2] A variant was used by UNIVAC's 1100-series computers.[3] Treating the code as a six-bit code these systems used a 36-bit word (capable of storing six such reduced FIELDATA characters).[4]

### Braille six-bit code

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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

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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.

## Examples of BCD six-bit codes

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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.

CDC 1604: Magnetic tape BCD codes  | 0  | 1  | 2  | 3  | 4  | 5  | 6  | 7  | 8  | 9  | A  | B  | C  | D  | E  | F

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0x  |  | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 0 | # | @ |  |  | TAPE
MARK
1x  |  SP | / | S | T | U | V | W | X | Y | Z | REC
MARK | , | % |  |  |
2x  | - | J | K | L | M | N | O | P | Q | R | -0 | $ | * |  |  |
3x  | & | A | B | C | D | E | F | G | H | I | +0 | . | ¤ |  |  | GRP
MARK
CDC 1604: Punched card codes  | 0  | 1  | 2  | 3  | 4  | 5  | 6  | 7  | 8  | 9  | A  | B  | C  | D  | E  | F

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0x  |  | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 0 | = | − |  |  |
1x  |  SP | / | S | T | U | V | W | X | Y | Z |  | , | ( |  |  |
2x  | — | J | K | L | M | N | O | P | Q | R | -0 | $ | * |  |  |
3x  | + | A | B | C | D | E | F | G | H | I | +0 | . | ) |  |  |
CDC 1612: Printer codes (business applications)  | 0  | 1  | 2  | 3  | 4  | 5  | 6  | 7  | 8  | 9  | A  | B  | C  | D  | E  | F

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0x  | : | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 0 | = | ≠ | ≤ | ! | [
1x  |  SP | / | S | T | U | V | W | X | Y | Z | ] | , | ( | → | ≡ | ~
2x  | − | J | K | L | M | N | O | P | Q | R | % | $ | * | ↑ | ↓ | >
3x  | + | A | B | C | D | E | F | G | H | I | < | . | ) | ≥ | ? | ;

## Examples of six-bit ASCII variants

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DEC SIXBIT  | 0  | 1  | 2  | 3  | 4  | 5  | 6  | 7  | 8  | 9  | A  | B  | C  | D  | E  | F

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0x  |  SP | ! | " | # | $ | % | & | ' | ( | ) | * | + | , | - | . | /
1x  | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | : | ; | < | = | > | ?
2x  | @ | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O
3x  | P | Q | R | S | T | U | V | W | X | Y | Z | [ | \ | ] | ^ | _
ECMA-1  | 0  | 1  | 2  | 3  | 4  | 5  | 6  | 7  | 8  | 9  | A  | B  | C  | D  | E  | F

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0x  |  SP |  HT |  LF |  VT |  FF |  CR |  SO |  SI | ( | ) | * | + | , | - | . | /
1x  | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | : | ; | < | = | > | ?
2x  |  NUL | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O
3x  | P | Q | R | S | T | U | V | W | X | Y | Z | [ | \ | ] |  ESC |  DEL
ICL Mainframes  | 0  | 1  | 2  | 3  | 4  | 5  | 6  | 7  | 8  | 9  | A  | B  | C  | D  | E  | F

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0x  | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | : | ; | < | = | > | ?
1x  |  SP | ! | " | # | £ | % | & | ' | ( | ) | * | + | , | - | . | /
2x  | @ | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O
3x  | P | Q | R | S | T | U | V | W | X | Y | Z | [ | $ | ] | ↑ | ←
SixBit ASCII (used by AIS)[5] | 0  | 1  | 2  | 3  | 4  | 5  | 6  | 7  | 8  | 9  | A  | B  | C  | D  | E  | F

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0x  | @ | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O
1x  | P | Q | R | S | T | U | V | W | X | Y | Z | [ | \ | ] | ^ | _
2x  |  SP | ! | " | # | $ | % | & | ' | ( | ) | * | + | , | - | . | /
3x  | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | : | ; | < | = | > | ?

## GOST 6-bit code

[edit]

See also: GOST 10859 § 6-bit code: with only Cyrillic upper case letters

GOST 6-bit code  | 0  | 1  | 2  | 3  | 4  | 5  | 6  | 7  | 8  | 9  | A  | B  | C  | D  | E  | F

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0x  | 0  | 1  | 2  | 3  | 4  | 5  | 6  | 7  | 8  | 9  | \+  | \-  | /  | ,  | .  |  SP
1x  | ⏨  | ↑  | (  | )  | × | =  | ;  | [  | ]  | *  | ‘  | ’  | ≠  | < | > | :
2x  | А | Б | В | Г | Д | Е | Ж | З | И | Й | К | Л | М | Н | О | П
3x  | Р | С | Т | У | Ф | Х | Ц | Ч | Ш | Щ | Ы | Ь | Э | Ю | Я | DEL

## Example of six-bit Braille codes

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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).[6][7]

| Hex  | ASCII Glyph  | Braille Dots  | Braille Glyph  | Braille Meaning

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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

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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

[edit]

* 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

[edit]

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) [1999]. "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

[edit]

* "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
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Character encodings

Early telecommunications|

* Telegraph code
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* T.51/ISO/IEC 6937
* ITU T.61
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ISO/IEC 8859|

* Approved parts
* -1 (Western Europe)
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* -3 (Maltese/Esperanto)
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* -5 (Cyrillic)
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Bibliographic use|

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National standards|

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ISO/IEC 2022|

* ISO/IEC 8859
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Mac OS Code pages
("scripts")|

* Armenian
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DOS code pages|

* 437
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* 3846
* ABICOMP
* CS Indic
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IBM AIX code pages|

* 895
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* 912
* 915
* 921
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* 1006
* 1008
* 1009
* 1010
* 1012
* 1013
* 1014
* 1015
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* 1046
* 1124
* 1133

Windows code pages|

* CER-GS
* 932
* 936 (GBK)
* 950
* 1169
* Extended Latin-8
* 1250
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* 1255
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* 1270
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EBCDIC code pages|

* Japanese language in EBCDIC
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DEC terminals (VTx)|

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Platform specific|

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Unicode / ISO/IEC 10646|

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* Comparison of Unicode encodings

TeX typesetting system|

* Cork
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Miscellaneous code pages|

* ABICOMP
* ASMO 449
* Digital encoding of APL symbols
* ISO-IR-68
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* HZ
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* Symbol
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* 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

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