IBM card sorter

An IBM card sorter is a machine for sorting decks of punched cards in the format popularized by the International Business Machines Corporation (IBM), which dominated the punched card data processing industry for much of the twentieth century. Sorting was a major activity in most facilities that processed data on punched cards using unit record equipment. The work flow of many processes required decks of cards to be put into some specific order as determined by the data punched in the cards. The same deck might be sorted differently for different processing steps. The IBM 80 series sorters sorted input cards into one of 13 pockets depending on the holes punched in a selected column and the sorter's settings.

The basic operation of a card sorter is to take a punched card, examine a single column, and place the card into a selected pocket. There are twelve rows on a punched card, and thirteen pockets in the sorter; one pocket is for blanks, rejects, and errors. (IBM 1962)

Cards are normally passed through the sorter face down with the bottom edge ("9-edge") first. A small metal brush or optical sensor is positioned so that, as each card goes through the sorter, one column passes under the brush or optical sensor. The holes sensed in that column together with the settings of the sorter controls determine which pocket the card is to be directed to. This directing is done by slipping the card into a stack of metal strips (or chute blades) that run the length of the sorter feed mechanism. Each blade ends above one of the output pockets, and the card is thus routed to the designated pocket.

Multiple column sorting was commonly done by first sorting the least significant column, then proceeding, column by column, to the most significant column. This is called a least significant digit radix sort.

Numeric columns have one punch in rows 0-9, possibly a sign overpunch in rows 11-12, and can be sorted in a single pass through the sorter. Alphabetic columns have a zone punch in rows 12, 11, or 0, a digit punch in one of the rows 1-9, and can be sorted by passing some or all of the cards through the sorter twice on that column. For more details of punched card codes see Punched card#IBM 80-column punched card formats and character codes.

There were several methods used for alphabetical sorting, depending on the features provided by the particular sorter and the characteristics of the data to be sorted. A commonly used method on the 082 and earlier sorters was to sort the cards twice on the same column, first on digit rows 1-9, then on the zone rows 12, 11, and 0 (or vice versa, zone rows first then digit rows). Operator switches allow zone-sorting by "switching off" rows 1-9 for the second pass of the card for each column.

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