Unit record equipment
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Before the advent of electronic computers, data processing was performed using electromechanical devices called unit record equipment, electric accounting machines (EAM) or tabulating machines. A data processing shop would have at least one of the most of the machine types. Data processing consisted of feeding decks of punch cards through the various machines in a carefully choreographed progression. The flow of card decks between the machines was typically hand-drawn on large sheets of paper using standardised symbols for the various functions.
Electronic accounting machines were as ubiquitous in industry and government in the first half of the twentieth century as computers became in the second half. The largest supplier of unit record equipment was IBM. This article reflects IBM practice and terminology.
Data Storage
The basic unit of data was the 80-column punch card. Each column represented a single digit, letter or special character. Data values consisted of a field of adjacent columns. An employee number might occupy 5 columns; hourly pay rate, 3 columns; hours actually worked in a given week, 2 columns; department number 3 columns; project charge code 6 columns and so on.Data was entered on the cards by a worker sitting at a machine called a key punch. The key punch had a keyboard similar to a typewriter and hoppers for blank and punched cards. Later model key punches (e.g. the IBM 026) printed the value of each column punched at the top of the card. In some cases decks of punched cards were then sent to a second machine called a verifier, which looked a lot like a key punch. Its operator entered the exact same data as the keypuncher, but the verifier machine merely checked to see if the data was the same. Valid cards had a small notch punched on the right hand edge.
Sorting
A major activity in any unit record shop was sorting decks of punch card into the proper order as determined by information punched in the card. The same deck might be sorted differently depending on the processing step. Sorters, like the IBM 80-series Card Sorters, took an input deck and sorted it into one of 13 output bins depending on which hole was punched in a selected column. The 13th bin was for blanks and rejects.Data processing tasks typically ran on a daily batch processing cycle. All the data cards punched during the day were sorted and merged with a master deck, which was then tabulated.
Tabulating
Reports and summary data were generated by accounting or tabulating machines (e.g. the IBM 407). The sorted deck was fed through the tabulating machine and each card was printed on its own line. Selected fields from each card were added to the value of one of several counters. At some signal, say a card with a special punch indicating it was a master card, a summary line would be produced containing the summed values.
Automatic Card Punchers
- Gang Punch - these would produce a large number of identically punched card, say for inventory tickets.
- Reproducing Punch - these could reproduce a deck of card in its entirety or they might just reproduce selected fields. A payroll master deck might be reproduced at the end of a pay period with the hours worked and net pay fields blank and ready for the next pay period's data. Programmers used these to make backups.
- Summary Punch - these were attached to tabulating machines and could record summary line on punch cards for later use.
- Mark Sense reader - these would detect pencil marks on bubbles printed on the card and punch the corresponding data values into the card.
Specialized machines
- Collators - these machines had two input hoppers and four or more output hoppers. They could merge or match card decks based on the plug-board's program.
- Interpreter - these machines would print the values of columns along the top of the card.
- Decollator - separated multi-part printed forms into separate stacks of printout and removed the carbon paper.
- Burster - separated the perforations between pages.
Programming
Unit record equipment (except for sorters) were programmed using a plug-board control panel. The panels had a matrix of holes organized into groups. A supply of wires with metal ferrules at each end were available. Each end of the wire would snap into one of the holes on the control and protrude out the back. The tips of the ferrules would be pressed against a matrix of contacts on the machine when the board was latched into place. The output from some card column positions might be fed into a tabulating machine's counter, for example. A shop would typically have separate plug-boards for each task a machine was used for.
Different length wires were of different colours, to help prevent dense piles of wires from building up. Wires could also be temporary or permanent - permanent wires had little latches on the ferrules, and required a special tool to remove them. These were typically used once a board had been debugged.
Unit Record Equipment in the Computer Age
Early computer programming shops used punch cards for program entry and storage. A typical corporate or university computer lab would have a room full of key punch machines for programmer use. An old 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. The 519 could also punch sequential numbers in columns 73-80 of Cobol or Fortran program decks. Those languages and others reserved those columns for this purpose. An IBM 80-series sorter would be used to put things back in order if a sequenced deck was dropped. (A quicker, but less effective, protection against dropped card decks was drawing a diagonal line across the top of the deck with a marking pen.)Early mid-sized commercial computers, such as the IBM 1401 were designed to work with punch card operations and allowed more complex reporting. However many shops soon began using magnetic tape as their primary storage medium, using cards primarily for data input.
Many organizations loathe to alter systems that are working, so production unit record installations remained in operation long after computers offered faster and more cost effective solutions. Specialized uses of punch cards, including toll collection, microfilm aperture cards, and punch card voting, keep unit record equipment in use into the twenty-first century.
The IBM System/3, the original ancestor of the entire IBM midrange computer product line, was developed as a replacement for plugboard-programmable unit record machines.
See also
- IBM System 3 which introduced a 96-column card.
- List of IBM products
- List of UNIVAC products
External links
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