Display code is the

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 punc ...

used by many computer systems manufactured by

Control Data Corporation Control Data Corporation (CDC) was a mainframe and supercomputer firm. CDC was one of the nine major United States computer companies through most of the 1960s; the others were IBM, Burroughs Corporation, DEC, NCR, General Electric, Honeywel ...

, notably the CDC3000 series and the following

CDC 6000 series The CDC 6000 series is a discontinued family of mainframe computers manufactured by Control Data Corporation in the 1960s. It consisted of the CDC 6200, CDC 6300, CDC 6400, CDC 6500, CDC 6600 and CDC 6700 computers, which were all extremely rapid a ...

in 1964. The

and their successors had 60 bit words. As such, typical usage packed 10 characters per word. It is a six-bit extension of the four-bit BCD encoding, and was referred to as BCDIC (BCD interchange code.) There were several variations of display code, notably the 63-character character set, and the 64-character character set. There were also 'CDC graphic' and '

ASCII ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because of ...

graphic' variants of both the 63- and 64-character sets. The choice between 63- or 64-character character set, and between CDC or ASCII graphic was site-selectable. Generally, early CDC customers started out with the 63-character character set, and CDC graphic print trains on their

line printer A line printer prints one entire line of text before advancing to another line. Most early line printers were impact printers. Line printers are mostly associated with unit record equipment and the early days of digital computing, but the ...

s. As time-sharing became prevalent, almost all sites used the ASCII variant - so that line printer output would match interactive usage. Later CDC customers were also more likely to use the 64-character character set. A later variation, called 6/12 display code, was used in the Kronos and NOS timesharing systems in order to support full

capabilities. In 6/12 mode, an escape character (the circumflex, octal 76) would indicate that the following letter was lower case. Thus, upper case and other characters were 6 bits in length, and lower case characters were 12 bits in length. The

PLATO system Plato ( ; grc-gre, Πλάτων ; 428/427 or 424/423 – 348/347 BC) was a Greek philosopher born in Athens during the Classical period in Ancient Greece. He founded the Platonist school of thought and the Academy, the first institution ...

used a further variant of 6/12 display code. Noting that lower case letters were most common in typical PLATO usage, the roles were reversed. Lower case letters were the norm, and the escape character preceded upper case letters. The typical text file format used a ''zero-

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

terminator'' to signify the end of each record. The zero-byte terminator was indicated by, at least, the final twelve bits of a 60-bit word being set to zero.CDC often used the term ''

'' to refer to 12-bit quantities, even though characters were only 6-bits long. The terminator could actually be anywhere from 12- to 66-bits long - depending on the length of the record. This caused an ambiguity in the 64-character character set, when a colon character needed to be the final character in a record. In such cases a blank character was typically appended to the record after the trailing colon.

Display code characters (64-character character set version)

6/12 display code

The NOS 6/12 display code is one of the character sets used on

CDC Cyber The CDC Cyber range of mainframe-class supercomputers were the primary products of Control Data Corporation (CDC) during the 1970s and 1980s. In their day, they were the computer architecture of choice for scientific and mathematically inten ...

NOS computers to represent all

characters.

External links

Charsets for CDC machines
{{character encoding Character sets Control Data Corporation software

Display code characters (64-character character set version)

6/12 display code

Further reading

External links