The Harvard Mark I, also known as the Automatic Sequence Controlled Calculator (ASCC), was an electromechanical computer constructed between 1943 and 1944 for the IBM Corporation and the Harvard University Computation Laboratory. It was one of the earliest large-scale automatic digital computers and the first to be used at a university.
Development and Design
The project was initiated by Howard Aiken, a Harvard graduate who conceived the idea of an automatic computing machine in the late 1930s. Aiken collaborated with IBM engineers, primarily J. Presper Eckert, John Mauchly, and later the IBM team led by IBM president Thomas J. Watson. The design combined mechanical components (e.g., rotating shafts, relays, and switches) with electrical circuits to perform arithmetic operations.
Physical Characteristics
- Length: Approximately 51 feet (15.5 m)
- Height: About 8 feet (2.4 m)
- Weight: Roughly 5 tons (4,540 kg)
- The machine occupied a large room at Harvard’s New England Complex and consisted of 765,000 moving parts, including 3,000 miles (4,800 km) of wire.
Technical Specifications
- Arithmetic: Fixed-point decimal arithmetic with 23-digit precision.
- Operation Speed: Approximately 3 additions or subtractions per second; multiplication took about 6 seconds, division about 15 seconds.
- Memory: Utilized a series of mechanical counters for storage; later versions incorporated electro-mechanical registers.
- Input/Output: Input via punched paper tape; output via teleprinter and punched tape.
- Control: Program control was achieved through a paper tape with punched holes representing instructions.
Historical Usage
- World War II: Deployed for calculations related to naval gunnery, ballistic trajectories, and cryptographic work.
- Scientific Research: Assisted in early computational work in physics, such as calculations for the Manhattan Project and later in astronomy and meteorology.
- Education: Served as a teaching tool for early computer science concepts at Harvard and other institutions.
Legacy
The Harvard Mark I marked a transition from purely mechanical calculators to programmable digital computers. Its design principles influenced subsequent electronic computers, notably the Harvard Mark II (ASCC II) and later electronic projects such as the IBM 701. The machine demonstrated the feasibility of automated, programmable computation and contributed to the development of computer engineering as a discipline.
Preservation
A portion of the original Harvard Mark I, including its control panel and select mechanical components, is on display at the Harvard Science Center. Additional artifacts and documentation are maintained by the Smithsonian Institution’s National Museum of American History.