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IBM 7090/94 Character Representation

The 7090/94 used six-bit representations for characters for a total of 64 possible characters -- the BCD character set. However, only 51 were commonly used:

BCD Character Set
CharacterBCD (Binary/Octal)CharacterBCD (Binary/Octal)CharacterBCD (Binary/Octal)
'4'000100/04'I'011001/31' ' (Blank)110000/60
' " ' (Double Quote)001100/14'L'100011/43'X'110111/67

The [Special-1] character was, apparently, a "+/0" character and [Special-2] was, apparently, an 'O' with a horizontal bar across the top. The characters read by the card reader were defined by the plug-board programming on the IBM 711 card reader and could vary slightly from site to site.

With six-bit characters, each 36-bit word of memory could hold up to six characters. The six-character string "MOTHER" would be represented in a 36-word of memory as the binary string:


or, in octal, as:


Source code (and data) were usually loaded into the 7090/94 from 80-column punched cards (typically indirect through magnetic tape). The paper cards usually could contain up to 80 characters of information in a horizontal line with each character containing data in 12 vertical positions.

Counting, in a single character position of 12 vertical positions, from the top to the bottom of the card, the positions were denoted as 12-punch, 11-punch, 0-punch, 1-punch, 2-punch,... 9-punch as follows:

The code that was used to read characters from cards was as follows:
  • 12-Punch and 1-Punch together in a column: 'A', 12-2: 'B', 12-3: 'C', 12-4: 'D', 12-5: 'E', 12-6: 'F', 12-7: 'G', 12-8: 'H', 12-9: 'I'

  • 11-Punch and 1-Punch together in a column: 'J', 11-2: 'K', 11-3: 'L', 11-4: 'M', 11-5: 'N', 11-6: 'O', 11-7: 'P', 11-8: 'Q', 11-9: 'R'

  • 0-Punch and 2-Punch together in a column: 'S', 0-3: 'T', 0-4: 'U', 0-5: 'V', 0-6: 'W', 0-7: 'X', 0-8: 'Y', 0-9: 'Z'

  • For numeric '1' through '9', punch only the number omitting all three of the top columns (12-Punch, 11-Punch, 0-Punch)

  • Special Characters (e.g., comma, period, etc.) required special groupings of punches -- Last Revision: 23 August 2001
Copyright © 1996 - 2017 Jack Harper (unless otherwise noted)
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