Punched Card and Card Readers

Punch card is a rigid piece of paper containing rows and column of numbers. It is put into a keypunch machine which place holes in to represent the data. This pattern of representing data as punched holes is known as Hollerith code. A card reader interpretes these holes to translate the punched information into a machine readable code and then send to the CPU for processing.
Punched cards are rarely used today. However, you may occasionally encounter in large companies such as public utilities, where they are still used for billing.