原创 How it used to be: Paper tapes and punched cards (Part 3)

[Continued from How it used to be: Paper tapes and punched cards (Part 2)]

Due to the fact that teleprinters were relatively inexpensive (compared to the millions of dollars invested in the computer), a typical installation usually included a large number of them, thereby allowing many people to create programs at the same time. Groups of programs were subsequently presented to the computer operators in a batch, and the computer was said to be running in a batch mode. (Things continue to evolve, and the phrase "batch mode" is now commonly used to refer to a program that's running as a background task, using whatever resources are available when interactive users aren't hogging all of the computer's capacity.)

As computers evolved and became more powerful, teleprinters began to be connected directly to them. This allowed the operators and the computer to communicate directly with each other, which was one of the first steps along the path towards the interactive way in which we use computers today.

The origin of punched cards

The practice of punching holes in cards to record data dates back to the early 1800s, when a French silk weaver called Joseph Marie Jacquard invented a way of automatically controlling the warp and weft threads on a silk loom by recording patterns as holes in a string of thin wooden boards or cards. In the years to come, variations on Jacquard's punched cards were to find a variety of uses, including representing music to be played by automated pianos and programs to be executed by computers.

The first practical use of punched cards for data processing is credited to the American inventor Herman Hollerith. During the 1880s, Hollerith decided to use Jacquard's punched cards to represent the data gathered for the American census, and to read and collate this data using an automatic machine. The resulting tabulating machines were successfully used to gather and process the data from the 1890 census, and Hollerith's company grew from strength to strength.

In addition to solving the census problem, Hollerith's machines proved themselves to be extremely useful for a wide variety of statistical applications, and some of the techniques they used were to become significant in the development of the digital computer. In February 1924, Hollerith's company changed its name to International Business Machines, or IBM.

Many references state that Hollerith originally made his punched cards the same size as the dollar bills of that era, because he realised that it would be convenient and economical to buy existing office furniture – such as desks and cabinets – that already contained receptacles to accommodate stacks of bills. Other sources consider this to be a popular fiction. Whatever the case, we do know that these cards were eventually standardised at 7.375 inches by 3.25 inches, and Hollerith's many patents permitted his company to hold an effective monopoly on punched cards for many years. (Hollerith, who was no one's fool, had quickly realised that the real money was not to be made in the tabulating machines themselves, but rather in the tens or hundreds of thousands of cards that were used to store data.)

Although other companies came up with innovative ways to bypass Hollerith's patents, they failed to capitalise on their advances, thereby giving IBM a chance to regain the high ground. For example, Hollerith's early cards were punched with round holes, because his prototype machine employed cards with holes created using a tram conductor's ticket punch. Hollerith continued to use round holes in his production machines, which effectively limited the amount of data that could be stored on each card. By the early 1900s, Hollerith's cards supported 45 columns, where each column could be used to represent a single character or data value.

This set the standard until 1924-1925, when the Remington Rand Corporation evolved a technique for doubling the amount of information that could be stored on each card. But they failed to exploit this advantage to its fullest extent, and, in 1929-1931, IBM responded by using rectangular holes, which allowed them to pack 80 columns of data onto each card. Although other formats appeared sporadically (including some from IBM), the 80 column card overwhelmingly dominated the punched card market from around the 1950s onward.

IBM 80-column punched card format

The above illustration shows one of the early 80 column IBM cards (approximately full size). Each card contains 12 rows of 80 columns, and each column is typically used to represent a single piece of data such as a character. The top row is called the "12" or "Y" row; the second row from the top is called the "11" or "X" row; and the remaining rows are called the '0' to '9' rows (indicated by the numbers printed on the cards).

This figure (which took one heck of a long time to draw let me tell you) illustrates one of the early, simpler coding schemes, in which each character could be represented using no more than three holes. (Note that we haven't shown all of the different characters that could be represented). Over the course of time, more sophisticated coding schemes were employed to allow these cards to represent different character sets such as ASCII and EBCDIC; the rows and columns stayed the same, but different combinations of holes were used.

[To be continued at How it used to be: Paper tapes and punched cards (Part 4)]