![]() A mainframe computer could cost millions of dollars and usage was measured in seconds per job. Use of this expensive equipment was often charged to a user's account. Because programs were run in batch-mode processing it might be a considerable time before any hardcopy printed or punched output was produced, and put into these same cubby holes – however, on a lightly-used system, it was possible to make alterations and rerun a program in less than an hour.ĭedicated programmers might stay up well past midnight to get a few quick turnarounds. After reading the cards in, the computer operator would return the card deck – typically to one of a set of alphabetically labelled cubby holes, based on the programmer's last initial. 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. These cards (e.g., a JCL "JOB" card to start a new job) were often pre-punched in large quantities in advance. 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 they removed them from the stacker. To solve that problem, the card reader could be reinstalled (or initially installed) outside of the computer room to allow programmers to do " self-service" job submission. During peak times, it was common to stand in line waiting to submit a deck. ![]() In such 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. An IBM 519 might be provided to reproduce program decks for backup or to punch sequential numbers in columns 73-80. 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 proofreading. Nearby would be a room full of keypunch machines for programmer use. IBM's huge size and industry footprint often caused many of their conventions to be adopted by other vendors, so the example below is fairly similar to most places, even in non-IBM shops.Ī typical corporate or university computer installation would have a suite of rooms, with a large, access-restricted, air-conditioned room for the computer (similar to today's server room) and a smaller quieter adjacent room for submitting jobs. an NCR, ICL, Hewlett-Packard (HP) or Control Data shop would have NCR, ICL, HP, or Control Data computers, printers and so forth, but have IBM 029 keypunches. The description below describes an all-IBM shop (a "shop" is programmer jargon for a programming site) but shops using other brands of mainframes (or minicomputers) would have similar equipment although because of cost or availability might have different manufacturer's equipment, e.g. In smaller organizations programmers might do their own punching, and in all cases would often have access to a keypunch to make small changes to a deck. The editing of programs was facilitated by reorganizing the cards, and removing or replacing the lines that had changed programs were backed up by duplicating the deck, or writing it to magnetic tape. ![]() Often another keypunch operator would then take that deck and re-punch from the coding sheets – but using a "verifier" such as the IBM 059 that checked that the original punching had no errors.Ī typing error generally necessitated re-punching an entire card. These forms were then taken by keypunch operators, who using a keypunch machine such as the IBM 026 (later IBM 029) punched the deck. Often programmers first wrote their program out on special forms called coding sheets, taking care to distinguish the digit zero from the letter O, the digit one from the letter I, eight from B, two from Z, and so on using local conventions such as the " slashed zero". The term is often used interchangeably with punch card, the difference being that an unused card is a "punch card," but once information had been encoded by punching holes in the card, it was now a "punched card." For simplicity, this article will use the term punched card to refer to either. ![]() Groups or "decks" of cards form programs and collections of data. A punched card is a flexible write-once medium that encodes data, most commonly 80 characters. ![]()
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