Before the advent of electronic computers
, data processing was performed using electromechanical devices called unit record equipment
, electric accounting machines
) or tabulating machines
. Unit record machines were as ubiquitous in industry and government in the first half of the twentieth century as computers
became in the second half. They allowed large volume, sophisticated, data-processing tasks to be accomplished long before modern (electronic) computers were invented. This data processing
was accomplished by processing decks of punched cards
through various unit record machines in a carefully choreographed progression. This progression, or flow, from machine to machine was often planned and documented with drawings that used standardised symbols for the various machine functions – drawings that today would be called flowcharts
. The machines all had high-speed mechanical feeders to process from around one hundred cards per minute, to 2,000 cards per minute, sensing punched holes with either electrical or optical sensors. The operation of many machines was directed by the use of a removable control panel
. Initially all machines were constructed using electromechanical counters and relays. Electronic components were introduced on some machines beginning in the late 1940s.
developed punched card and unit record technology for the 1890 census and founded the Tabulating Machine Company
(1896) which was one of three companies that merged to form Computing Tabulating Recording Corporation
(CTR), later renamed IBM
. IBM manufactured and marketed a variety of unit record machines for creating, sorting, and tabulating punched cards, even after expanding into computers in the late 1950s. IBM developed punch card technology into a powerful tool for business data-processing and produced an extensive line of general-purpose unit record machines
. By 1950, the IBM card and IBM unit record machines had become ubiquitous in industry and government. The warning often printed on cards that were to be individually handled, "Do not fold, spindle or mutilate," became a motto for the post-World War II
era (even though many people had no idea what spindle
meant). The largest supplier of unit record equipment was IBM
and this article largely reflects IBM practice and terminology.
The basic unit of data storage was the 80-column punched card
. Each punched 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.
Original data was usually punched into cards by workers, often women, known as key punch operators. Their work was often checked by a second operator using a verifier machine. Cards were also produced automatically by various unit record machines and later by computer output devices.
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
, sorted an input deck into one of 13 output bins
depending on which hole was punched in a selected column. The 13th bin was for blanks and rejects. Sorting an input deck into ascending sequence on a multiple column field, such as an employee number, was done by a radix sort
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.
Reports and summary data were generated by accounting or tabulating machines. 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.
For many applications, the volume of paper produced by tabulators required other machines, not considered to be unit record machines, to ease paper handling.
- A decollator separated multi-part printed forms into separate stacks of printout and removed the carbon paper.
- A burster separated the perforations between pages of fan-fold output.
Card punching machines included:
- Gang punch - these would produce a large number of identically punched cards—for example, for inventory tickets.
- Reproducing punch - these could reproduce a deck of cards 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. Computer programmers who created their programs in the form of punch card decks used these to make backups.
- Summary punch - these were attached to tabulating machines and could punch new cards with details and totals from the tabulating machine.
- Mark sense reader - these would detect pencil marks on bubbles printed on the card and punch the corresponding data values into the card.
Later "document origination machines" such as the IBM 519 could perform all of the above operations.
Collating and interpreting
had two input hoppers and four or more output hoppers. These machines could merge or match card decks based on the control panel's program.
An interpreter would print characters equivalent to the values of columns on the card. The columns to be printed could be selected and even reordered, based on the machine's control panel wiring. Later models could print on one of several rows on the card. Unlike keypunches, which printed values directly above each column, interpreters generally used a font that was a little wider than a column and could only print up to 60 characters per row. Typical later models include the IBM 550 Numeric Interpreter and the IBM 557 Alphabetic Interpreter.
Transmission Of Punched Card Data
Electrical transmission of punch card data was invented in the early 1930s. The device was called an Electrical Remote Control of Office Machines and was assigned to IBM.
Inventors were Joseph C. Bolt of Boston & Curt I. Johnson; Worcester, Mass. assors to the Tabulating Machine Co., Endicott, NY. The Distance Control Device received a US patent in Aug.9,1932: pat# 1,870,230. Letters from IBM talk about filling in Canada in 9/15/1931.
Processing Punched Tape
The IBM 046 Tape-to-Card Punch and IBM 047 Tape-to-Card Printing Punch were almost identical, with the exception of the printing mechanism. These machines read data from punched paper tape and punched that data into punched cards.
See Punched tape.
The operation of most unit record equipment (except for sorters) was directed by a plug-board control panel (IBM did not use the term "programming" for these machines). The panels had a matrix of holes organized into groups. Wires with metal ferrules at each end were place in the holes to make connections. 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.
Unit record equipment in the computer age
Early computer installations used punched 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 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
program decks. Those languages and others did not use those columns; the use of only 72 columns is a tradition tracing back to the IBM 704
card reader. 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 were loath to alter systems that were 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, microform 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.
Guide to the unit record equipment articles