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The IBM 421 accounting machine saw use in the 1960s. It accepted 80-column punch cards and its printing mechanism handled the upper-case letters of the alphabet, the decimal digits 0 to 9, a period (.), and plus and minus signs.
The operation of the 421 was directed by the use of a removable control panel and a carriage tape. By means of the control panel, any column of the card could be wired to any print column, by means of a wire link (the end terminals of which were inserted into slots in the control panel). When the control panel wiring was complete, the control panel was inserted into the guides in the machine, and a hand-operated lever moved the control panel so that the wire links made contact with corresponding terminals in the machine.
The 421 had 64 positions of memory, typically used to store data off a lead punch card. There were also three external program switches, Minor, Major and SuperMajor that were used to alter the function of the plug board Program Selectors. The 421 sold in the UK was capable of totaling amounts in the pre-1970 currency with twenty shillings to the pound and 12 pennies to the shilling.
The 421 could be cable attached to another device (514?) that was referred to as a Summary or Gang Punch and was used to punch out cards with summary totals tallied by the 421.
Printing speed was about 100 lines per minute. When forming totals, printing was suppressed, and the card reader mechanism read cards at an increased speed of about 150 cards per minute.
There was one type bar for each print column. Each type bar had every character in the available set. When printing a column of a card, the type bar was raised until the desired character was in position at the current line, and then the type bar was hit by a "hammer", thus impressing the character onto the paper. The entire line was printed simultaneously (that is, all hammers struck simultaneously).
The tabulator's uses included
- tabulating (listing) punch cards
- forming totals
- forming grand totals.
An interesting use of the machine was the evaluation of polynomials.