Early computers did not have the advanced storage devices we have today. Information in early computers was typically stored on punched cards, where holes and no holes represented 0s and 1s. The basic principle is similar to today’s disks, which use magnetic media to represent 0s and 1s. These punched cards were known as punch cards, named after Hollerith cards or IBM cards. They were blank cards with holes made either manually or by machines. The holes on the cards represented data or instructions for the computer. In the early days of computing, punch cards were a widely used method for inputting information. These cards were fed into a card reader connected to the computer, and the series of holes on the cards were converted into digital information.
For example, early computer programmers had to write programs by hand and convert them into a series of punch cards using a card punch machine. Then, the programmer would feed the stack of cards into a card reader as a way to input the program. Today, we will discuss the following aspects:
- How do punch cards work?
- How do we read a punch card?
- The history of punch cards Why were punch cards used?
- Are punch cards still in use?
- Are punch cards input devices?
1. How do punch cards work?
Using the punch card machine shown in the above image, data can be written onto the card by punching different holes in each column to represent different characters. Below is an example of a punch card.
Once a punch card is completed, or a carriage return key is entered, the card is technically “storing” that information. Because each card can only store a certain amount of information, if you write a program using punch cards, you need a stack of ordered cards (with each card representing one line of code).
To load the program or read the data on the cards, each card needs to be placed into a card reader, which will read the information into the computer. When a card is placed into the reader, it starts reading from the top left corner, reading the contents of one column from top to bottom before moving to the next column. The card reader reads the information column by column.
2. How do humans read card contents?
Most later cards had the information printed at the top, so you could check the top of the card to see what was stored. If an error was found on the card, it would be re-punched. If no data was printed at the top, humans had to know what numbers the punches represented and manually translate each column. This is similar to understanding that binary 01101000 and 01101001 equals 104 and 105, which spells “hi” in ASCII.
3. The history of punch cards
If we trace back, the earliest use of punch cards dates to 1725. At that time, punch cards were not used in computers but in looms. For example, Joseph Marie Jacquard used punch cards to create a woven silk portrait of himself. In 1832, Semen Korsakov used these cards to store and search information. In the late 1890s, Herman Hollerith invented a method to record and store punch card information for the U.S. Census. He later founded what we know today as IBM.
4. Why were punch cards used?
Early computers could not store files as modern computers do. Therefore, if you wanted to create a data file or program usable by the computer, the only way was through punch cards. As magnetic media were invented, punch cards gradually fell out of use.
5. Are punch cards still in use?
Punch cards were a method of storing information in the 1900s and started being replaced by other storage media after the 1960s. Today, punch cards are rarely, if ever, used.
6. Are punch cards input devices?
Technically, no, punch cards themselves are not input devices, but the card reader can be considered an input device. The card reader reads the punch card data into the computer. This is similar to the concept of CDs and CD drives. A floppy disk itself is not an input device because it is just a storage medium, whereas the floppy drive is considered an input device.
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