Acomputer punched card reader or justcomputer card reader is acomputer input device used to readcomputer programs in either source or executable form anddata frompunched cards. Acomputer card punch is a computeroutput device that punches holes in cards. Sometimes computer punch card readers were combined with computer card punches and, later, other devices to form multifunction machines.
Many early computers, such as theENIAC, and theIBM NORC, provided for punched card input/output.[1] Card readers and punches, either connected to computers or inoff-line card to/frommagnetic tape configurations, were ubiquitous through the mid-1970s.
Punched cards had been in use since the 1890s; their technology was mature and reliable. Card readers and punches developed forpunched card machines were readily adaptable for computer use.[2] Businesses were familiar with storing data on punched cards andkeypunch machines were widely employed. Punched cards were a better fit for some computer applications than other 1950s technologies, such asmagnetic tape, because individual cards could easily be updated without having to access a computer. Also file drawers of punched cards served as a low-density offline storage medium for data.
The standard measure of speed iscards per minute, abbreviated CPM: The number of cards which can be read or punched in one minute. Card reader models vary from 150 to around 2,000 CPM.[3][4] At 1200 CPM, i.e. 20 cards per second, this translates to 1,600 characters per second (CPS), assuming all 80 columns of each card encode information.
Early computer card readers were based on electromechanicalunit record equipment and used mechanicalbrushes that make anelectrical contact for a hole, and no contact if there was no hole. Later readers usedphotoelectric sensors to detect the presence or absence of a hole. Timing within each read cycle relates the resulting signals to the corresponding position on the card. Early readers read cards in parallel, row by row, following unit record practice (hence the orientation of the rectangular holes). Later, card readers that read cards serially, column by column became more common.
Card punches necessarily run more slowly to allow for the mechanical action of punching, up to around 300 CPM or 400 characters per second.[5]
Some card devices offer the ability tointerpret, or print a line on the card displaying the data that is punched. Typically this slows down the punch operation. Many punches would read the card just punched and compare its actual contents to the original data punched, to protect against punch errors. Some devices allowed data to be read from a card and additional information to be punched into the same card.
Readers and punches include ahopper for input cards and one or morestacker bins to collect cards read or punched. A function calledstacker select allows the controlling computer to choose which stacker a card just read or punched will be placed into.
Documation Inc., of Melbourne, Florida, made card readers forminicomputers in the 1970s:
Their card readers have been used in elections,[11] including the2000 "chads" election in Florida.[12]
For some computer applications,binary formats were used, where each hole represented a single binary digit (or "bit"), every column (or row) is treated as a simple bitfield, and every combination of holes is permitted. For example, the IBM 711 card reader used with the704/709/7090/7094 series scientific computers treated every row as two 36-bit words, ignoring 8 columns. (The specific 72 columns used were selectable using aplugboard control panel, which is almost always wired to select columns 1–72.) Sometimes the ignored columns (usually 73–80) were used to contain a sequence number for each card, so the card deck could be sorted to the correct order in case it was dropped.
An alternative format, used by theIBM 704's IBM 714 native card reader, is referred to as Column Binary or Chinese Binary, and used 3 columns for each 36-bit word.[14] Later computers, such as theIBM 1130 orSystem/360, used every column. TheIBM 1401's card reader could be used in Column Binary mode, which stored two characters in every column, or one 36-bit word in three columns when used as input device for other computers. However, most of the older card punches were not intended to punch more than 3 holes in a column. Themultipunch key is used to produce binary cards, or other characters not on the keypunch keyboard.[15]
As aprank, in binary mode, cards could be punched where every possible punch position had a hole. Such "lace cards" lacked structural strength, and would frequently buckle and jam inside the machine.[16]
.jpg)
