Punched card input/output

Documation Inc.
Industry	Computer hardware
Founded	1970s
Headquarters	Melbourne, United States
Products	Card readers (M-200, M-600, M-1000-L)

A computer punched card reader, also known as a computer card reader, is a computer input device designed to interpret programs and data encoded on punched cards. Conversely, a computer card punch functions as an output device that creates holes in cards. Certain units combined both reading and punching capabilities, and later incorporated additional features into multifunctional apparatuses.

History

Early computing machines such as the ENIAC and IBM NORC utilized punched cards for input and output operations. Throughout the mid-1970s, card readers and punches remained prevalent, either directly interfaced with computers or employed offline alongside magnetic tape storage.

Having been in use since the 1890s, punched cards represented a well-established technology. Devices originally built for unit record processing were readily adapted to computer applications. Keypunch machines were extensively employed by businesses to encode data onto punched cards. Compared with magnetic tape, punched cards offered the advantage of straightforward updates without needing computer access and served as a form of low-density offline data storage.

Operation

The performance of card readers is typically indicated in cards per minute (CPM), with speeds ranging from approximately 150 up to 2,000 CPM. At a rate of 1,200 CPM (equivalent to 20 cards per second), this translates to around 1,600 characters per second if all 80 columns contain data.

Initial card readers detected holes using electromechanical brushes; subsequent models transitioned to photoelectric sensors. Early designs read cards by scanning rows in parallel, whereas later devices processed cards serially, column by column.

Card punches generally operate at slower speeds due to mechanical limitations, commonly achieving up to 300 CPM or about 400 characters per second.

Some punching devices include an interpreter that prints a human-readable line on the card representing the punched information, which reduces punching speed. Many machines incorporate verification by reading back the punched card to ensure accuracy. Certain models permit reading existing data on a card and adding additional punches without erasing prior information.

Both readers and punches feature an input hopper for feeding cards and one or multiple stacker bins for collecting output cards. A stacker select mechanism enables systems controlling the device to route cards into designated output bins.

Control Data Corporation

CDC 405 — card reader for the CDC 6000 series, operating at either 1200 or 1600 CPM
CDC 415 — card punch designed for the CDC 6000 series, with a speed of 250 CPM

Documation

Documation Inc., based in Melbourne, Florida, manufactured card readers aimed at minicomputer systems during the 1970s:

M-200 card reader capable of processing 300 cards per minute; also marketed by DEC as the CR-11 for the PDP-11
M-600 card reader with a throughput of 600 CPM; rebranded by HP as models 2892A and 2893A
M-1000-L card reader that reads up to 1,000 cards per minute

These readers found application in electoral processes, notably during the 2000 Florida election recount involving "chads".

IBM

IBM 711 — vacuum tube-era peripheral card reader offering speeds of 150 or 250 CPM
IBM 2501 — card reader available at either 600 or 1000 CPM
IBM 1402 — high-speed combined reader/punch introduced alongside the IBM 1401, capable of processing 800 CPM
IBM 1442 — reader/punch designed for the more affordable IBM 1440, reading between 80 and 400 CPM and punching from 91 up to 355 CPM
IBM 2540 — reader/punch derived from the IBM 1402, released with the advent of System/360
IBM 2560 Multi-Function Card Machine (MFCM) tailored for the IBM System/360 Model 20, featuring capabilities such as collating, sorting, printing, and interpreting punched cards
IBM 3505 reader along with the companion IBM 3525 reader/printer/punch designed for the System/370 (introduced in 1971), delivering reading speeds of up to 1200 CPM and punching speeds of approximately 300 CPM

Binary encoding

Certain systems utilized binary encoding formats, where each punched hole signified a single bit, permitting all possible hole patterns. For instance, the IBM 711 card reader designed for the 704/709/7090/7094 series interpreted each row as two 36-bit words, disregarding eight columns. The 72 columns in use could be customized through a plugboard control panel, commonly configured for columns 1 through 72. Columns that were ignored—typically columns 73 to 80—often contained sequence numbers to preserve the order of card decks if they were accidentally dropped.

Another approach, known as Column Binary or Chinese Binary and employed by the IBM 714 reader for the IBM 704, allocated three columns per 36-bit word. Subsequent machines such as the IBM 1130 and System/360 utilized every column available. The IBM 1401 reader was capable of operating in Column Binary mode, enabling storage of two characters per column or a single 36-bit word across three columns when interfacing with other computer systems. Nonetheless, most earlier punch machines were limited to punching no more than three holes per column; the multipunch key allowed for binary cards or characters extending beyond the standard keyboard repertoire.

As a form of mischief in binary mode, cards could be punched with all holes present (known as "lace cards"), which compromised their structural integrity and frequently caused jams in equipment.

Punched card equipment