Hollerith removable plugboard believed to be from a Hollerith Tabulator and Accounting Machine such as a Hollerith (IBM) Type 3-S Tabulator, numeric only, mid-to-late 1920s. First model to include direct subtraction and regular negative number notation (as opposed to requiring users to write negative numbers in 9's complement). This example was one of the first to use the removeable plug board.

The Direct Subtraction Tabulating Accounting Machine, Type 3-S is a multiple subtracting, adding, classifying, and printing machine which automatically produces complete printed reports from punched tabulating cards. It prints classifications, lists details, computes and prints totals, grand totals, and net balances.

An automatic control causes the machine to stop at the completion of each data group; the total and group indication are recorded, then the machine clears itself and starts on the next group. An Automated Plugboard eliminates the necessity of plugging the machine just before printing the reports.

A plugboard, or control panel (the term used depended on the application area), is an array of jacks, or hubs, into which patch cords can be inserted to complete an electrical circuit. Control panels were used to direct the operation of some unit record equipment. Plugboards were used on some cipher machines, and some early computers.

An early example can be seen at http://www.columbia.edu/cu/computinghistory/wl-gallery/plugboards.html

Our plugboard is in excellent condition and is believed to be from about 1935. If any one can provide more accurate information, please email us at collection@computinghistory.org.uk 

This was kindly donated by John Somerfield.