Punched card reader

A computer punched card reader or just computer card reader is a computer input device used to read executable computer programs and data from punched cards under computer control. A computer card punch is a computer output device that punches holes in cards under computer control. Sometimes computer card readers were combined with computer card punches and, later, other devices to form multifunction machines.

Most early computers, such as the ENIAC, and the IBM NORC, provided for punched card input/output. Card readers and punches, either connected to computers or in off-line card to/from magnetic tape configurations, were ubiquitous through the mid-1970s.

Punched cards had been in use since the 1890s; their technology was mature and reliable. Card readers and punches developed for punched card machines were readily adaptable for computer use. Businesses were familiar with storing data on punched cards and keypunch machines were widely employed. Punched cards were a better fit than other 1950s technologies, such as magnetic tape, for some computer applications as individual cards could easily be updated without having to access a computer.

The standard measure of speed is cards per minute, abbreviated CPM: The number of cards which can be read or punched in one minute. Card reader models vary from 300 to around 2000 CPM. If all columns of an 80 column card encode information this translates to approximately 2500 characters per second (CPS).

Cards may be read using mechanical brushes that make an electrical contact for a hole, and no contact if no punch, or photoelectric sensors that function similarly. Timing relates the signals to the position on the card. Cards may be read serially, column by column, or in parallel, row by row.

Card punches necessarily run more slowly to allow for the mechanical action of punching, up to around 300 CPM or 400 characters per second.

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