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

Parity bit

A parity bit is a bit that is added to ensure that the number of bits with the value one in a set of bits is even or odd. Parity bits are used as the simplest form of error detecting code....

 were a natural way of storing data on 7-track

IBM 7 Track

IBM's first magnetic tape data storage devices, introduced in 1952, use what is now generally known as 7 track tape. The magnetic tape is 1/2" wide and there are 6 data tracks plus 1 parity track for a total of 7 parallel tracks that span the length of the tape...

 magnetic tape

Magnetic tape data storage

Magnetic tape data storage uses digital recording on to magnetic tape to store digital information. Modern magnetic tape is most commonly packaged in cartridges and cassettes. The device that performs actual writing or reading of data is a tape drive...

.

Types of sixbit codes

Six-bit BCD was used by IBM

IBM

International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...

. This encoding was replaced by the 8-bit EBCDIC

EBCDIC

Extended Binary Coded Decimal Interchange Code is an 8-bit character encoding used mainly on IBM mainframe and IBM midrange computer operating systems....

 code when System/360

System/360

The IBM System/360 was a mainframe computer system family first announced by IBM on April 7, 1964, and sold between 1964 and 1978. It was the first family of computers designed to cover the complete range of applications, from small to large, both commercial and scientific...

 standardized on 8-bit byte

Byte

The byte is a unit of digital information in computing and telecommunications that most commonly consists of eight bits. Historically, a byte was the number of bits used to encode a single character of text in a computer and for this reason it is the basic addressable element in many computer...

s. There are some variants of this type of code (see below).

Some six-bit variants were derived from ASCII

ASCII

The American Standard Code for Information Interchange is a character-encoding scheme based on the ordering of the English alphabet. ASCII codes represent text in computers, communications equipment, and other devices that use text...

. One popular variant was DEC

Digital Equipment Corporation

Digital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...

 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 filename

Filename

The filename is metadata about a file; a string used to uniquely identify a file stored on the file system. Different file systems impose different restrictions on length and allowed characters on filenames.A filename includes one or more of these components:...

s and assembler

Assembly language

An assembly language is a low-level programming language for computers, microprocessors, microcontrollers, and other programmable devices. It implements a symbolic representation of the machine codes and other constants needed to program a given CPU architecture...

 symbol

Identifier

An identifier is a name that identifies either a unique object or a unique class of objects, where the "object" or class may be an idea, physical [countable] object , or physical [noncountable] substance...

s could be stored in a single 36-bit word of PDP-10

PDP-10

The PDP-10 was a mainframe computer family manufactured by Digital Equipment Corporation from the late 1960s on; the name stands for "Programmed Data Processor model 10". The first model was delivered in 1966...

. It was also used in COBOL databases, where end-of-record information was stored separately. This code, with added odd parity bit

Parity bit

A parity bit is a bit that is added to ensure that the number of bits with the value one in a set of bits is even or odd. Parity bits are used as the simplest form of error detecting code....

, is used on Track 1 of magnetic stripe card

Magnetic stripe card

A magnetic stripe card is a type of card capable of storing data by modifying the magnetism of tiny iron-based magnetic particles on a band of magnetic material on the card...

s, as specified in ISO/IEC 7811-2. Uuencode

Uuencode

Uuencoding is a form of binary-to-text encoding that originated in the Unix program uuencode, for encoding binary data for transmission over the uucp mail system.The name "uuencoding" is derived from "Unix-to-Unix encoding"...

 utilizes this character set for text representation of arbitrary binary data.

A DEC SIXBIT code including a few control characters — along with SO/SI

Shift Out and Shift In characters

Shift Out and Shift In are ASCII control characters 14 and 15, respectively .  The original meaning of those characters was to switch to a different character set and back.  This was used, for instance, in the Russian character set known as KOI7, where SO starts printing Russian...

, allowing code extension — was specified as ECMA

Ecma International

Ecma International is an international, private non-profit standards organization for information and communication systems. It acquired its name in 1994, when the European Computer Manufacturers Association changed its name to reflect the organization's global reach and activities...

-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

PDP-8

The 12-bit PDP-8 was the first successful commercial minicomputer, produced by Digital Equipment Corporation in the 1960s. DEC introduced it on 22 March 1965, and sold more than 50,000 systems, the most of any computer up to that date. It was the first widely sold computer in the DEC PDP series of...

.

Fieldata

Fieldata

Fieldata was a pioneering computer project run by the US Army Signal Corps in the late 1950s that intended to create a single standard for collecting and distributing battlefield information...

 was a six-bit format used by UNIVAC's

UNIVAC

UNIVAC is the name of a business unit and division of the Remington Rand company formed by the 1950 purchase of the Eckert-Mauchly Computer Corporation, founded four years earlier by ENIAC inventors J. Presper Eckert and John Mauchly, and the associated line of computers which continues to this day...

 1100-series computers. These systems used a 36-bit word (capable of storing 6 Fieldata characters).

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

Punched card

A punched card, punch card, IBM card, or Hollerith card is a piece of stiff paper that contains digital information represented by the presence or absence of holes in predefined positions...

 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	<	.	)	≥	?	;

Example of sixbit ASCII variant

ECMA-1 : DEC SIXBIT with control characters

.0	.1	.2	.3	.4	.5	.6	.7	.8	.9	.A	.B	.C	.D	.E	.F
0.	space	HT	LF Newline In computing, a newline, also known as a line break or end-of-line marker, is a special character or sequence of characters signifying the end of a line of text. The name comes from the fact that the next character after the newline will appear on a new line—that is, on the next line below the...	VT	FF Page Break A page break is a marker in an electronic document that tells the document interpreter that the content which follows is part of a new page. A page break causes a form feed to be sent to the printer during spooling of the document to the printer.-Form feed:...	CR Carriage return Carriage return, often shortened to return, refers to a control character or mechanism used to start a new line of text.Originally, the term "carriage return" referred to a mechanism or lever on a typewriter...	SO	SI	(	)	*	+	,	-	.	/
1.	0	1	2	3	4	5	6	7	8	9	:	;	<	=	>	?
2.	NULL Null character The null character , abbreviated NUL, is a control character with the value zero.It is present in many character sets, including ISO/IEC 646 , the C0 control code, the Universal Character Set , and EBCDIC...	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 Escape character In computing and telecommunication, an escape character is a character which invokes an alternative interpretation on subsequent characters in a character sequence. An escape character is a particular case of metacharacters...	DEL Delete key The delete key , known less ambiguously as forward delete, performs a function when struck on a computer keyboard during text or command editing, which is to discard the character ahead of the cursor's position, moving all following characters one position "back" towards the freed letterspace. The...

External links

• SIXBIT Character Code Reference Digital Equipment Corporation SIXBIT character coding system