Punch Card Machinery

The punch card (or "Hollerith" card) is a recording medium for holding information for use by automated data processing machines. Made of thin cardboard, the punch card represents information by the presence or absence of holes in predefined positions on the card. (See Figure 4.3.0 and 4.3.1 below) In the first generation of computing, from the 1920s into the 1950s, punch cards were the primary medium for data storage and processing. Eventually, during the late 1970s to early 1980s, the punch card was phased out as a medium for storage of computer data and was replaced by huge floppy disks.

Punch cards are now obsolete, outside of a few legacy systems and specialized applications.

The method used in Punched Cards is quite simple: On a piece of light-weight cardboard, successive positions either have a hole punched through them or are left intact. The rectangular bits of paper punched out are called ‘chads’. Thus, each punch location on the card represents a single binary digit (or "bit"). Each column on the card contains several punch positions (multiple bits). A major reason for the corner cut was to ensure that the punch card could not be inserted backwards or upside down. If the punch card was inserted backwards or upside down it hit a small plastic pin in the machine called the corner cut pin. This would engage a micro switch and halt the machine operation until the card was inserted correctly with the corner cut on the correct side of the punch card as used in that system. Stopping the machine meant the machine would not continue to sort or validate.

Let us look at some of the advantages of using punch cards. Punch Cards were inexpensive and provided a permanent record of each transaction. Large organizations had warehouses filled with punch card records.

If the punched cards had advantages, why did they become obsolete? As you know, the Punched card machines were used to input data using punch cards.Punched-card systems fell out of favor in the mid to late 1970s, as disk storage became cost effective and affordable interactive terminals meant that users could edit their work with the computer directly rather than requiring the intermediate step of 

the punched cards.