Zoë Blade's notebook

IBM Card

IBM Card tech specs

  • Released: 1928[1]
  • Company: IBM
  • Type: Punched card
  • Capacity: 80 12-bit words (120 bytes)

The IBM Card was a 7⅜×3¼″ punched card format by IBM. The original version introduced in 1928 consisted of 80 columns × 10 rows of punchable cells per sheet of card. In 1930, this was updated to 80 columns × 12 rows.[1] Each cell represented one bit of information, so in theory the card as a whole could store eighty 12-bit words.

In practice, punched cards in general usually sacrificed efficient storage for the sake of being friendlier to people who weren't familiar with manually storing binary data, which was (and still is) pretty much everyone.

As such, each column typically only needed one of the lower ten holes punched, to represent that digit, for instance, or that specific letter in the part of the alphabet signified by the top three holes (reusing row zero). This means that most of the time, IBM Cards were storing closer to 80 6-bit words than the 80 12-bit words they were technically capable of, fulfilling only half their capacity.

To make matters worse, the IBM 704, 709, and 7090 mainframe computers could only read 72 columns (defaulting to the first 72 in particular, which few clients saw a need to change). The card reader would read in each of the twelve rows as two 36-bit words.[2] The computer could then rearrange these into their original 72 columns of 12-bit values, and finally translate those into the actual 72 6-bit values to store in its RAM.

So a card capable of storing up to 960 bits of information was much more likely to be storing 432 bits, or thereabouts — a mere 45% of their capacity. At least the unreadable last 8 columns could be repurposed by other equipment to automatically order the cards, in case anyone accidentally dropped them. Anyone who couldn't afford such equipment simply drew a single diagonal line across the top edge of all the cards.

The later System/360 could read all 80 columns, and encouraged more combinations of holes per column for various punctuation marks in its 8-bit EBCDIC character set. It was therefore using the equivalent of 640 bits per card, exactly two thirds their capacity.

A typical filing cabinet could theoretically hold about 5 MB of data stored on 42,000 punched cards. In practice, for the IBM 704 this was closer to 2.25 MB, and for the System/360 it was closer to 3.3 MB.[3]

The de facto standard of 72 or 80 characters per line persists to this day.

Notably, IBM rented punched card technology to the Nazis, and printed custom cards for them, to help them commit genocide against Jewish people and other minority groups.[4] While the technology itself isn't inherently good or evil, it can certainly be put to horrific uses.

References

  1. "The IBM Punched Card" IBM Heritage
  2. "IBM 7090 owner's manual" IBM, Mar 1962, pp. 96—98
  3. "These cabinets each have 12 trays, each of which holds approximately 3,500 cards, for an overall capacity of 42,000 cards per cabinet." Principles of Punched Card Data Processing Robert G. Van Ness, 1967, p. 155
    Note: At 120 bytes per IBM Card, 120 bytes × roughly 3,500 cards = roughly 420,000 bytes per tray; × 12 trays = 5,040,000 bytes per filing cabinet.
  4. IBM and the Holocaust Edwin Black, 2001, ISBN 0-609-60799-5

Further reading

Official webpage

80 characters per line: IBM Card

Data storage media: CD | Cassette tape | Cassette tape as a data storage medium | DAT | Floppy disk | IBM Card | MiniDisc | microSD card

IBM: IBM Card