Harvard Mark I

The Harvard Mark I, officially known as the IBM Automatic Sequence Controlled Calculator (ASCC), was a landmark in computing history. It was one of the earliest general-purpose electromechanical computers. This means it was designed to perform a wide variety of mathematical tasks automatically. During the final years of World War II, the machine played a vital role in major scientific efforts. It was a significant step forward because it could automate the execution of complex, long calculations.

To understand how the Mark I functioned, one must look at its massive physical design. The machine was housed in a steel frame that stood 51 feet long and 8 feet high. It relied on 765,000 electromechanical components to process information. These components included switches, relays, rotating shafts, and clutches. The system also utilized hundreds of miles of wire with three million individual connections. To keep everything synchronized, a drive shaft was coupled to an electric motor. This motor served as both the main power source and the system clock.

The machine processed data through a specific sequence of mechanical and electrical steps. It read its instructions from a 24-channel punched paper tape. The machine would execute one instruction and then move to the next one on the tape. The 24 channels on the tape were divided into three fields of eight channels each. The first field provided a binary index for the result of an operation. The second field provided the source datum, or the starting number. The third field contained a code that told the machine which operation to perform.

Calculating speeds varied depending on the complexity of the math involved. The Mark I could perform three additions or subtractions every single second. Multiplication was slower, taking about 6 seconds to complete. Division required 15.3 seconds. For much more difficult tasks, such as a logarithm or a trigonometric function, the machine took over one minute. Despite these speeds, it was much more precise than many other tools of its time. For example, it could compute values to eighteen decimal places.

The origins of the Mark I trace back to Howard Aiken's studies at Harvard University. In 1935, while studying physics, Aiken conceived of a large-scale calculating machine. He initially faced rejection from the Monroe Calculator Company and Harvard itself. However, he eventually presented his proposal to IBM in November 1937. IBM chairman Thomas Watson Sr. approved the project and its funding in February 1939. IBM engineers then built the ASCC at their Endicott, New York, plant in early 1943. The machine was shipped to Harvard and officially presented to the university on August 7, 1944.

The Mark I had a profound impact on the Manhattan Project. In March 1944, physicist John von Neumann used the machine to study implosion. He needed to determine if implosion was a viable way to detonate an atomic bomb. The Mark I provided much higher precision than the modified IBM punched-card machines used by other groups. While other machines computed to six decimal places, the Mark I reached eighteen decimal places. This precision allowed the team to integrate partial differential equations at a much smaller interval size.

In the years following its debut, the Mark I influenced a series of successor machines. Howard Aiken continued his work with the Harvard Mark II, which arrived around 1947 or 1948. The Mark III, released in 1949, began using electronic components like vacuum tubes and crystal diodes. Finally, the Mark IV was developed in 1952 as an all-electronic machine using magnetic core memory. The original Mark I was disassembled in 1959. Portions were distributed to IBM, the Smithsonian Institution, and the Harvard Collection of Historical Scientific Instruments. Today, parts of the machine are located at the Harvard Science and Engineering Complex in Allston, Massachusetts.