Punched Cards
Punched cards are the testimony of an old technology for storing and inserting data in the 60s / 70s computers. A punch card is a rectangular cardboard sheet on which holes were made using special machines. It is a form of binary memory where a specific location has a hole punched (representing 1) or not (representing 0).
The two cards in my possession have 80 columns and 12 rows (IBM format). As the number of holes is little, it is evident that the capacity (in terms of bytes) of these cards was very limited. Actually, each card was used to store a single instruction line, and a full deck of cards was needed to store a full program.
The reading device, on the other hand, was quite sofisticated as it used a photoelectric sensor device (definitely not organic, as the technology was not yet invented :P). The punched card was irradiated by the light and the reader detects the light through the holes on the card to reconstruct the information.
Interesting, to allow the use of punched cards in the correct direction in the reading devices, each card is provided with a cut corner in order to allow the devices to verify the correct insertion of the punched card before starting the reading operation.
Punched cards were used as data storage device until the 1960s-1970s. Then, the spread of other storage media based on electromagnetism like magnetic tapes for the Commodore 64, floppy disks for the Apple II, etc.. makes punch card technology obsolete.
