CDC display code
| Industry | Computer hardware and software |
|---|---|
| Founded | 1957 |
| Headquarters | United States |
Display code refers to the six-bit character code employed by numerous computer systems developed by Control Data Corporation, particularly the CDC 6000 series (1964), the 7600 (1967), and the Cyber series (1971). These machines utilized 60-bit words, commonly storing 10 characters within each word. This code represents a six-bit enhancement of the four-bit BCD encoding, also identified as BCDIC (BCD interchange code).
Overview
Multiple versions of display code were created, including sets containing 63 or 64 characters, each available in 'CDC graphic' and 'ASCII graphic' forms. Initially, users employed the 63-character set combined with CDC graphic print trains on line printers. With the rise of time-sharing systems, most installations shifted to the ASCII variant to ensure uniformity between interactive sessions and printed outputs. Eventually, the 64-character set became preferred by later users.
The 6/12 display code emerged during the era of the Kronos and NOS time-sharing systems to provide comprehensive support for ASCII. In this configuration, an escape character (the circumflex symbol, octal 76) signaled that the subsequent letter was lowercase, allowing uppercase and other characters to remain six bits while lowercase letters were extended to twelve bits.
Conversely, the PLATO system implemented a variant where lowercase letters served as the default, and an escape character was used before uppercase letters.
Text files commonly concluded records with a zero-byte terminator, which meant that at least the last twelve bits of a 60-bit word were set to zero. The length of this terminator depended on the record size, leading to ambiguity in the 64-character set when a record ended with a colon; in these instances, a space character was appended after the colon.
64-character character set version
010110||22||26||V||V||
010111||23||27||W||W||
011000||24||30||X||X||
011001||25||31||Y||Y||
011010||26||32||Z||Z||
011011||27||33||0||0||
011100||28||34||1||1||
011101||29||35||2||2||
011110||30||36||3||3||
011111||31||37||4||4||
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100000||32||40||5||5||
100001||33||41||6||6||
100010||34||42||7||7||
100011||35||43||8||8||
100100||36||44||9||9||
100101|||37|||45|||+|||+||
100110|||38|||46|||–|||–||
100111|||39|||47|||*|||*||
101000|||40|||50|||/|||/||
101001|||41|||51|||(||(
101010|||42|||52|||)||)|
101011|||43|||53|||$|||$||
101100|||44|||54|||=|||=||
101101|||45|||55||| (blank)|| (blank)||
101110|||46|||56|||,|||,||
101111|||47|||57|||.|||.||
110000|||48|||60|||#|||≡ (equiv)||
110001|||49|||61|||[|||[||
110010|||50|||62|||]|||]||
110011|||51|||63%%% %%%
110100%%%52%%%64|" " (quote)||≠ (not eq)%%
%-
110101%%%53%%%65%%%→ (concat) [PASCAL '{']%%
%-
110110%%%54%%%66%%%!%%%∨ (log OR)%%
%-
110111%%%55%%%67%%%&%%%∧ (log AND)%%
%-
111000%%%56%%%70%%%' %%%↑ (super)%%
%-
111001%%%57%%%71%%%'?';;;↓ (sub) [PASCAL '}']%%
%-
111010%%%58%%%72%%% < %%% < %%%
%-
111011%%%59%%%73%%% > %%% > %%%
%-
111100%%%60%%%74%%%@ %%% ≤ %%%
%-
111101%%%61%%%75%%%\ %%% ≥ %%%
%-
111110%%%62%%%76%%%^ %%% ¬ (NOT) %%%
%-
111111%%%63%%%77%%% ; %%% ; %%%
6/12 display codeThe 6/12 display code is a character encoding scheme employed on CDC Cyber systems running the NOS to represent the complete range of ASCII characters.
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