Article snapshot taken from Wikipedia with creative commons attribution-sharealike license.
Give it a read and then ask your questions in the chat.
We can research this topic together.
Display code is the six-bit character code used by many computer systems manufactured by Control Data Corporation, notably the CDC 6000 series in 1964, the 7600 in 1967 and the following Cyber series in 1971. The CDC 6000 series 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.)
Overview
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 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 printers. 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 ASCII 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 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 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. 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
ASCII
CDC
Binary
Decimal
Octal
Graphic
Graphic
Name
000 000
0
00
:
:
colon
000 001
1
01
A
A
000 010
2
02
B
B
000 011
3
03
C
C
000 100
4
04
D
D
000 101
5
05
E
E
000 110
6
06
F
F
000 111
7
07
G
G
001 000
8
10
H
H
001 001
9
11
I
I
001 010
10
12
J
J
001 011
11
13
K
K
001 100
12
14
L
L
001 101
13
15
M
M
001 110
14
16
N
N
001 111
15
17
O
O
010 000
16
20
P
P
010 001
17
21
Q
Q
010 010
18
22
R
R
010 011
19
23
S
S
010 100
20
24
T
T
010 101
21
25
U
U
010 110
22
26
V
V
010 111
23
27
W
W
011 000
24
30
X
X
011 001
25
31
Y
Y
011 010
26
32
Z
Z
011 011
27
33
0
0
011 100
28
34
1
1
011 101
29
35
2
2
011 110
30
36
3
3
011 111
31
37
4
4
ASCII
CDC
Binary
Decimal
Octal
Graphic
Graphic
Name
100 000
32
40
5
5
100 001
33
41
6
6
100 010
34
42
7
7
100 011
35
43
8
8
100 100
36
44
9
9
100 101
37
45
+
+
100 110
38
46
-
-
100 111
39
47
*
*
101 000
40
50
/
/
101 001
41
51
(
(
101 010
42
52
)
)
101 011
43
53
$
$
101 100
44
54
=
=
101 101
45
55
blank
101 110
46
56
,
,
101 111
47
57
.
.
110 000
48
60
#
≡
equiv
110 001
49
61
[
[
110 010
50
62
]
]
110 011
51
63
%
%
110 100
52
64
"
≠
not eq
110 101
53
65
_
→
concat
110 110
54
66
!
∨
log OR
110 111
55
67
&
∧
log AND
111 000
56
70
'
↑
super
111 001
57
71
?
↓
sub
111 010
58
72
<
<
111 011
59
73
>
>
111 100
60
74
@
≤
111 101
61
75
\
≥
111 110
62
76
^
¬
NOT
111 111
63
77
;
;
CDC often used the term byte to refer to 12-bit quantities, even though characters were only 6-bits long.
Display code 00 has no associated graphic in the 63-character set
Display code 63 (octal) is a : (colon) in the 63-character set
In CDC PASCAL, this is the left brace, {, character
In CDC PASCAL, this is the right brace, }, character
6/12 display code
The NOS 6/12 display code is one of the character sets used on CDC CyberNOS computers to represent all ASCII characters.
Savard, John J. G. (2018) . "Computer Arithmetic". quadibloc. The Early Days of Hexadecimal. Archived from the original on 2018-07-16. Retrieved 2018-07-16.
Character sets