The age of the punched card

Before the advent of modern technologies like magnetic tape and video screens the most usual way to load a program on a computer was via punched tape or card. Of course this was at a time when computers typically filled rooms and were something few people had access to. Indeed computer time was limited and expensive and computers could only do one thing at a time. They couldn't sit around waiting for a programmer to type in his latest masterpiece while there was more important work to do such as the company payroll!

Therefore programs were entered offline using a separate system called a card or key punch such as the IBM 029. The programmer would enter their program (COBOL shown below) or job control instructions and these would be printed to cards, where a line of code (up to eighty characters) fitted on a card. Holes in the card and the absense of them representing the binary data.

Once the program was written the programmer would have a stack of cards, which for a standard data processing program could consist of hundreds of cards! These were handed over at the computer centre to be loaded onto the computer when it was free by one of the operators. Often this would be during the night. The programmer would return the next day to receive the print out and see if his program had worked or not! Punched cards remained the most usual way to load programs well into the 1970s, indeed IBM were still selling card punch machines in the 1980s.

Punched cards had their drawbacks compared to later storage media of course though were durable and human readable. Dropping a stack of cards was not the end of the world, though a labourious task putting them back in order!