Six-bit character code

Six-bit character codes were 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 sixbit codes

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 . 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; it includes the space, punctuation characters, numbers, and uppercase 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 two characters fit in each word of the PDP-1 and PDP-8.

COBOL databases sixbit code

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

Magnetic stripe card sixbit code

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

Uuencode sixbit code

Uuencode utilizes a sixbit character set for text representation of arbitrary binary data.

DEC sixbit code

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

Fieldata sixbit code

Fieldata was a six-bit format used by UNIVAC's 1100-series computers. These systems used a 36-bit word (capable of storing 6 Fieldata characters).

Braille sixbit 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.

Examples of BCD sixbit codes

CDC 1604 : Magnetic tape BCD codes

	.0	.1	.2	.3	.4	.5	.6	.7	.8	.9	.A	.B	.C	.D	.E	.F
0.		1	2	3	4	5	6	7	8	9	0	#	@			tape mark
1.	space	/	S	T	U	V	W	X	Y	Z	record mark	,	%
2.	−	J	K	L	M	N	O	P	Q	R	−0	$	*
3.	&	A	B	C	D	E	F	G	H	I	+0	.	¤			group mark

CDC 1604 : Punched card codes

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

Examples of sixbit ASCII variants

DEC SIXBIT:

	.0	.1	.2	.3	.4	.5	.6	.7	.8	.9	.A	.B	.C	.D	.E	.F
0.	space	!	"	#	$	%	&	'	(	)	*	+	,	-	.	/
1.	0	1	2	3	4	5	6	7	8	9	:	;	<	=	>	?
2.	@	A	B	C	D	E	F	G	H	I	J	K	L	M	N	O
3.	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
0.	space	HT	LF	VT	FF	CR	SO	SI	(	)	*	+	,	-	.	/
1.	0	1	2	3	4	5	6	7	8	9	:	;	<	=	>	?
2.	NULL	A	B	C	D	E	F	G	H	I	J	K	L	M	N	O
3.	P	Q	R	S	T	U	V	W	X	Y	Z	[	\	]	ESC	DEL

GOST 6-bit code

	_0	_1	_2	_3	_4	_5	_6	_7	_8	_9	_A	_B	_C	_D	_E	_F
0_	0 00 0	1 01 1	2 02 2	3 03 3	4 04 4	5 05 5	6 06 6	7 07 7	8 10 8	9 11 9	+ 12 10	- 13 11	/ 14 12	, 15 13	. 16 14	SP 17 15
1_	⏨ 20 16	↑ 21 17	( 22 18	) 23 19	× 24 20	= 25 21	; 26 22	[ 27 23	] 30 24	* 31 25	‘ 32 26	’ 33 27	≠ 34 28	< 35 29	> 36 30	37 31
2_	А 40 32	Б 41 33	В 42 34	Г 43 35	Д 44 36	Е 45 37	Ж 46 38	З 47 39	И 50 40	Й 51 41	К 52 42	Л 53 43	М 54 44	Н 55 45	О 56 46	П 57 47
3_	Р 60 48	С 61 49	Т 62 50	У 63 51	Ф 64 52	Х 65 53	Ц 66 54	Ч 67 55	Ш 70 56	Щ 71 57	Ы 72 58	Ь 73 59	Э 74 60	Ю 75 61	Я 76 62	DEL 77 63

Example of sixbit 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)

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