Computer programming in the punched card era

Punched card from a Fortran program.

From the invention of computer programming languages up to the mid-1980s, many if not most computer programmers created, edited and stored their programs on punched cards. The practice was nearly universal with IBM computers in the era. A punched card is a flexible write-once medium that encodes, most commonly, 80 characters of data. Groups or "decks" of cards form programs and collections of data. Users could create cards using a desk-sized keypunch with a typewriter-like keyboard. A typing error generally necessitated repunching an entire card. A single character typo could be corrected by duplicating the card up to the error column, typing the correct character and then duplicating the rest of the card. In some companies programmers wrote information on special forms called coding sheets, taking care to distinguish the digit zero from the letter O, the digit one from the letter I, 8's from Bs, 2's from Zs, and so on. These forms were then converted to cards by keypunch operators and, in some cases, checked by verifiers.

A box of punched cards with several program decks.
A single program deck, with individual subroutines marked. The markings show the effects of editing, as cards are replaced or reordered.

Many early programming languages, including Fortran, Cobol and the various IBM assembler languages, used only the first 72 columns of a card — a tradition that traces back to the IBM 711 card reader used on the IBM 704/709/7090/7094 series (especially the IBM 704, the first mass-produced computer with floating point arithmetic hardware), which could only read 72 of the 80 columns in one pass. Columns 73-80 were ignored by the compilers and could be used for identification or a sequence number so that if the card deck was dropped it could be restored to its proper order using a card sorter. Drawing a diagonal stripe across the top of the card deck provided a similar check for proper order. Programs were backed up by duplicating the deck or writing it to magnetic tape.

A pad of Fortran coding forms.

A typical corporate or university computer installation would have a room full of keypunch machines for programmer use. An IBM 407 Accounting Machine might be set up to allow newly created or edited programs to be listed (printed out on fan-fold paper) for proof reading. An IBM 519 might be provided to reproduce program decks for backup or to punch sequential numbers in columns 73-80. In many mainframe installations, known as closed shops, programmers submitted the program decks, often followed by data cards to be read by the program, to a person working behind a counter in the computer room. Many computer installations used cards with the opposite corner cut (sometimes no corner cut) as "job separators", so that an operator could stack several job decks in the card reader at the same time and be able to quickly separate the decks manually when he removed them from the stacker. These cards (e.g., a JCL "JOB" card to start a new job) were often prepunched in large quantities in advance.[1] This was especially useful when the main computer did not read the cards directly, but instead read their images from magnetic tape that was prepared offline by smaller computers such as the IBM 1401. After running it, the computer operator would return the card deck and any hardcopy printed output, typically to one of a set of alphabetically labelled cubby holes, based on the programmer's last initial.

Card formated for IBM 1620 assembly language.
Cards would sometimes jam in the reader, requiring one or more to be repunched.
Listing of a large computer program on continuous form paper, bound in a printout binder.

Overnight and 24 hour turnaround times were not uncommon; however, on a lightly used system, it was possible to make alterations and rerun a program in a few minutes. Between these extremes it was common to stand in line waiting to submit a deck. Dedicated programmers might stay up all hours to get a few quick turnarounds. Using this expensive equipment—mainframe computer usage was measured in seconds per job — was often charged to a user's account. Other installations, such as those using smaller computers like the IBM 650, 1620 and 1130, were run as an open shop, where programmers had use of the computer for a block of time. A keypunch was usually located nearby for quick corrections. This was all batch-mode processing, as opposed to interactive processing.


See also


External links


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Computer programming in the punch card era — From the invention of computer programming languages into the 1980s, many if not most computer programmers created, edited and stored their programs on punch cards. The practice was nearly universal with IBM computers in the era. In many… …   Wikipedia

  • Computer programming — Programming redirects here. For other uses, see Programming (disambiguation). Software development process Activities and steps …   Wikipedia

  • Punched card — Overpunch redirects here. For the code, see Signed overpunch. A punched card, punch card, IBM card, or Hollerith card is a piece of stiff paper that contains digital information represented by the presence or absence of holes in predefined… …   Wikipedia

  • Computer — For other uses, see Computer (disambiguation). Computer technology redirects here. For the company, see Computer Technology Limited. Computer …   Wikipedia

  • computer — computerlike, adj. /keuhm pyooh teuhr/, n. 1. Also called processor. an electronic device designed to accept data, perform prescribed mathematical and logical operations at high speed, and display the results of these operations. Cf. analog… …   Universalium

  • Computer keyboard — A key being pressed on a computer keyboard. In computing, a keyboard is a typewriter style keyboard, which uses an arrangement of buttons or keys, to act as mechanical levers or electronic switches. Following the decline of punch cards and paper… …   Wikipedia

  • History of computing hardware — Computing hardware is a platform for information processing (block diagram) The history of computing hardware is the record of the ongoing effort to make computer hardware faster, cheaper, and capable of storing more data. Computing hardware… …   Wikipedia

  • International Computers Limited — Former type Private Industry Computer hardware, Computer software Fate Acquired Successor Fujitsu Services Founded 1968 ( …   Wikipedia

  • History of operating systems — The history of computer operating systems recapitulates to a degree the recent history of computer hardware. Operating systems (OSes) provide a set of functions needed and used by most application programs on a computer, and the linkages needed… …   Wikipedia

  • IBM 1401 — The IBM 1401, the first member of the IBM 1400 series, was a variable wordlength decimal computer that was announced by IBM on October 5, 1959. It was withdrawn on February 8, 1971.From the [http://www… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.