Six-bit character code

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. Such codes with additional parity bit were a natural way of storing data on 7-track magnetic tape.

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 was used by IBM on early computers such as the IBM 704 in 1954.[1]^:p.35 This encoding was replaced by the 8-bit EBCDIC code 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. One popular variant 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 PDP-10, and three characters fit in each word of the PDP-1 and two characters fit in each word of the PDP-8.

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.

A UTF-6 encoding was proposed for Unicode[2] but was superseded by Punycode.

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 six-bit code

A DEC SIXBIT code including a few control characters—along with SO/SI, allowing code extension—was specified as ECMA-1 in 1963 (see 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).

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.[3] A variant was used by UNIVAC's 1100-series computers.[4] Treating the code as a six-bit code these systems used a 36-bit word (capable of storing six such reduced FIELDATA characters).[5]

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.

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.

Examples of BCD six-bit codes

Characters are shown 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
0_		1 0031	2 0032	3 0033	4 0034	5 0035	6 0036	7 0037	8 0038	9 0039	0 0030	# 0023	@ 0040			TAPE MARK
1_	SP 0020	/ 002F	S 0053	T 0054	U 0055	V 0056	W 0057	X 0058	Y 0059	Z 005A	RECORD MARK	, 002C	% 0025
2_	- 002D	J 004A	K 004B	L 004C	M 004D	N 004E	O 004F	P 0050	Q 0051	R 0052	-0 002D 0030	$ 0024	* 002A
3_	& 0026	A 0041	B 0042	C 0043	D 0044	E 0045	F 0046	G 0047	H 0048	I 0049	+0 002B 0030	. 002E	¤ 00A4			GROUP MARK

  Letter   Number   Punctuation   Symbol   Other   Undefined

CDC 1604: Punched card codes

	_0	_1	_2	_3	_4	_5	_6	_7	_8	_9	_A	_B	_C	_D	_E	_F
0_		1 0031	2 0032	3 0033	4 0034	5 0035	6 0036	7 0037	8 0038	9 0039	0 0030	= 003D	− 2212
1_	SP 0020	/ 002F	S 0053	T 0054	U 0055	V 0056	W 0057	X 0058	Y 0059	Z 005A		, 002C	( 0028
2_	— 2014	J 004A	K 004B	L 004C	M 004D	N 004E	O 004F	P 0050	Q 0051	R 0052	-0 002D 0030	$ 0024	* 002A
3_	+ 002B	A 0041	B 0042	C 0043	D 0044	E 0045	F 0046	G 0047	H 0048	I 0049	+0 002B 0030	. 002E	) 0029

CDC 1612: Printer codes (business applications)

	_0	_1	_2	_3	_4	_5	_6	_7	_8	_9	_A	_B	_C	_D	_E	_F
0_	: 003A	1 0031	2 0032	3 0033	4 0034	5 0035	6 0036	7 0037	8 0038	9 0039	0 0030	= 003D	≠ 2260	≤ 2264	! 0021	[ 005B
1_	SP 0020	/ 002F	S 0053	T 0054	U 0055	V 0056	W 0057	X 0058	Y 0059	Z 005A	] 005D	, 002C	( 0028	→ 2192	≡ 2261	~ 007E
2_	− 2212	J 004A	K 004B	L 004C	M 004D	N 004E	O 004F	P 0050	Q 0051	R 0052	% 0025	$ 0024	* 002A	↑ 2191	↓ 2193	> 003E
3_	+ 002B	A 0041	B 0042	C 0043	D 0044	E 0045	F 0046	G 0047	H 0048	I 0049	< 003C	. 002E	) 0029	≥ 2265	? 003F	; 003B

Examples of six-bit ASCII variants

DEC SIXBIT

	_0	_1	_2	_3	_4	_5	_6	_7	_8	_9	_A	_B	_C	_D	_E	_F
0_	SP 0020	! 0021	" 0022	# 0023	$ 0024	% 0025	& 0026	' 0027	( 0028	) 0029	* 002A	+ 002B	, 002C	- 002D	. 002E	/ 002F
1_	0 0030	1 0031	2 0032	3 0033	4 0034	5 0035	6 0036	7 0037	8 0038	9 0039	: 003A	; 003B	< 003C	= 003D	> 003E	? 003F
2_	@ 0040	A 0041	B 0042	C 0043	D 0044	E 0045	F 0046	G 0047	H 0048	I 0049	J 004A	K 004B	L 004C	M 004D	N 004E	O 004F
3_	P 0050	Q 0051	R 0052	S 0053	T 0054	U 0055	V 0056	W 0057	X 0058	Y 0059	Z 005A	[ 005B	\ 005C	] 005D	^ 005E	_ 005F

  Letter   Number   Punctuation   Symbol   Other   Undefined

ECMA-1

	_0	_1	_2	_3	_4	_5	_6	_7	_8	_9	_A	_B	_C	_D	_E	_F
0_	SP 0020	HT 0009	LF 000A	VT 000B	FF 000C	CR 000D	SO 000E	SI 000F	( 0028	) 0029	* 002A	+ 002B	, 002C	- 002D	. 002E	/ 002F
1_	0 0030	1 0031	2 0032	3 0033	4 0034	5 0035	6 0036	7 0037	8 0038	9 0039	: 003A	; 003B	< 003C	= 003D	> 003E	? 003F
2_	NUL 0000	A 0041	B 0042	C 0043	D 0044	E 0045	F 0046	G 0047	H 0048	I 0049	J 004A	K 004B	L 004C	M 004D	N 004E	O 004F
3_	P 0050	Q 0051	R 0052	S 0053	T 0054	U 0055	V 0056	W 0057	X 0058	Y 0059	Z 005A	[ 005B	\ 005C	] 005D	ESC 001B	DEL 007F

ICL Mainframes

	_0	_1	_2	_3	_4	_5	_6	_7	_8	_9	_A	_B	_C	_D	_E	_F
0_	0 0030	1 0031	2 0032	3 0033	4 0034	5 0035	6 0036	7 0037	8 0038	9 0039	: 003A	; 003B	< 003C	= 003D	> 003E	? 003F
1_	SP 0020	! 0021	" 0022	# 0023	£ 00A3	% 0025	& 0026	' 0027	( 0028	) 0029	* 002A	+ 002B	, 002C	- 002D	. 002E	/ 002F
2_	@ 0040	A 0041	B 0042	C 0043	D 0044	E 0045	F 0046	G 0047	H 0048	I 0049	J 004A	K 004B	L 004C	M 004D	N 004E	O 004F
3_	P 0050	Q 0051	R 0052	S 0053	T 0054	U 0055	V 0056	W 0057	X 0058	Y 0059	Z 005A	[ 005B	$ 0024	] 005D	↑ 2191	← 2190

SixBit ASCII (used by AIS)[6]

	_0	_1	_2	_3	_4	_5	_6	_7	_8	_9	_A	_B	_C	_D	_E	_F
0_	@ 0040	A 0041	B 0042	C 0043	D 0044	E 0045	F 0046	G 0047	H 0048	I 0049	J 004A	K 004B	L 004C	M 004D	N 004E	O 004F
1_	P 0050	Q 0051	R 0052	S 0053	T 0054	U 0055	V 0056	W 0057	X 0058	Y 0059	Z 005A	[ 005B	\ 005C	] 005D	^ 005E	_ 005F
2_	SP 0020	! 0021	" 0022	# 0023	$ 0024	% 0025	& 0026	' 0027	( 0028	) 0029	* 002A	+ 002B	, 002C	- 002D	. 002E	/ 002F
3_	0 0030	1 0031	2 0032	3 0033	4 0034	5 0035	6 0036	7 0037	8 0038	9 0039	: 003A	; 003B	< 003C	= 003D	> 003E	? 003F

GOST 6-bit code

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
0_	0 0030	1 0031	2 0032	3 0033	4 0034	5 0035	6 0036	7 0037	8 0038	9 0039	+ 002B	- 002D	/ 002F	, 002C	. 002E	SP 0020
1_	⏨ 23E8	↑ 2191	( 0028	) 0029	× 00D7	= 003D	; 003B	[ 005B	] 005D	* 002A	‘ 2018	’ 2019	≠ 2260	< 003C	> 003E	: 003A
2_	А 0410	Б 0411	В 0412	Г 0413	Д 0414	Е 0415	Ж 0416	З 0417	И 0418	Й 0419	К 041A	Л 041B	М 041C	Н 041D	О 041E	П 041F
3_	Р 0420	С 0421	Т 0422	У 0423	Ф 0424	Х 0425	Ц 0426	Ч 0427	Ш 0428	Щ 0429	Ы 042B	Ь 042C	Э 042D	Ю 042E	Я 042F	DEL 007F

  Letter   Number   Punctuation   Symbol   Other   Undefined

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).[7][8]

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

References

1. IBM Corporation (1954). 704 electronic data-processing machine: manual of operation (PDF).
2. Welter, Mark; Spolarich, Brian W. (2000-11-16). "UTF-6 - Yet Another ASCII-Compatible Encoding for ID". Internet Engineering Task Force. Archived from the original on 2016-05-23. Retrieved 2016-04-09.
3. Mackenzie, Charles E. (1980). Coded Character Sets, History and Development. The Systems Programming Series (1 ed.). Addison-Wesley Publishing Company, Inc. p. 64. ISBN 0-201-14460-3. LCCN 77-90165. ISBN 978-0-201-14460-4. Retrieved 2016-05-22.
4. Walker, John (1996-08-06). "UNIVAC 1100 Series FIELDATA Code". UNIVAC Memories. Archived from the original on 2016-05-22. Retrieved 2016-05-22.
5. Jennings, Thomas Daniel (2016-04-20) [1999]. "An annotated history of some character codes or ASCII: American Standard Code for Information Infiltration". World Power Systems (WPS). Archived from the original on 2016-05-22. Retrieved 2016-05-22.
6. Raymond, Eric S. (2017-08-29). "AIS Payload Data Types". catb.org. Retrieved 2017-11-16.
7. "Representing and Displaying Braille". DotlessBraille.org. 2002-02-20. Retrieved 2009-08-09.
8. Halleck, John (2000-08-24). "braille-ascii.ads". Braille.Ascii. 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" (PDF). (1.53 MB)
• SIXBIT Character Code Reference Digital Equipment Corporation SIXBIT character coding system