IBM card

Revision as of 22:32, 16 September 2014

The IBM card (originally produced by IBM, but later made by other companies as well) was a very common format of punched card for many years. Introduced in 1928 for use in tabulating machines, it became a major means of data input and storage for computers in the 1950s and 1960s, before being supplanted by terminals for input and magnetic tape (and later disks) for long-term storage.

The IBM card was 7 3/8" x 3 1/4", and had 80 columns of data, each of which had 12 positions for punching a rectangular hole, representing the digits 0 through 9 and two "zone punches" designated as X and Y or 11 and 12. (The top position was Y or 12, with X or 11 one position below it and then the digit punches from 0 to 9.)

A variety of encodings were used to store numbers, letters, symbols, and other data on the cards. The earliest system simplistically punched only one hole per column to store numeric data by punching the hole corresponding to each digit, with the zone punches used for signs and to designate special control cards. Later, letters, punctuation, and binary data were supported by codes involving multiple punches in a column, including EBCDIC. In theory, 12-bit words could be encoded one to a column, though most encodings in actual use were less information-dense (and, in fact, any encoding which allowed all holes of a card to be meaningfully punched at once could result in cards that had too many holes in them to maintain their structural integrity, and might jam card readers).

The printing on the cards came in a variety of formats for different applications; a common format was known as "IBM 5081", which had digits printed on it corresponding to the punch positions of the digits in each of the 80 columns.

The 80-column format of the IBM card inspired the use of 80-column-wide terminals, printers, and data formats such as the Internet e-mail message format (which suggests limiting lines to 78 characters, which when a carriage return and linefeed are added would reach 80). Some standards still in use today thus bear the marks of this old punched card format.

Later formats included the shortened IBM stub card, and the more compact IBM 96-column card.

References

• IBM card (Wikipedia)
• The Punched Card: shows details of a number of card formats and character encoding schemes
• Punched card emulator
• Vintagetech: company that specializes in recovering and converting old data including punched cards