Electromechanical Computer Component, Bell Telephone Laboratories Model 5, Motor with Paper Tape

This component of the Bell Telephone Laboratories Model V is a paper tape recorder. It has a black metal base with a black motor. A roll of paper tape is above.
The object is part of a very large programmable calculator built by Bell Telephone Laboratories of New York for the U.S. Army. By the mid-twentieth century, improving communications required complicated calculations. In order to improve the clarity and range of long distance voice signals, George Stibitz, a research mathematician at Bell Labs, needed to do calculations using complex numbers. Stibitz and Bell Labs engineer Sam Williams completed a machine for this purpose in 1939–it later was called the Bell Labs Model I. With the outbreak of World War II, Stibitz and Bell Labs turned their attention to calculations related to the aiming and firing of antiaircraft guns. Stibitz proposed a new series of relay calculators that could be programmed by paper tape to do more than one kind of calculation. The BTL Model 5 was the result. The machine consisted of twenty-seven standard telephone relay racks and assorted other equipment. It had over 9000 relays, a memory capacity of thirty seven-digit decimal numbers, and took about a second to multiply two numbers together. Two copies of the machine were built. This one was used by the U.S. Army for ballistics work at Aberdeen, Maryland and then at Fort Bliss, Texas. Machines that used relays were reliable, but slower than those using vacuum tubes, and soon gave way to electronic computers.
Currently not on view
Date made
Bell Telephone Laboratories
place made
United States: New Jersey, New Providence, Murray Hill
overall: 31.3 cm x 33 cm x 28 cm; 12 5/16 in x 13 in x 11 1/32 in
ID Number
accession number
catalog number
Credit Line
Gift of Bell Telephone Laboratories
See more items in
Medicine and Science: Mathematics
Computers & Business Machines
Data Source
National Museum of American History


Add a comment about this object