Computer History

The First Mainframe Computer: Harvard Mark I

The mainframe computer, or ‘big iron’ in the computer industry, is the longest-running computer system in history. This technology has been substantially useful since the World War II era. In fact, the first mainframe computer was used mainly by the US Navy during the war. Like supercomputers, the mainframe computer addressed the need for an automatic, large-scale calculator as a more efficient and error-free way of computing. It was the invention of such machines that redefined the term ‘computer’ to refer to devices that can carry out automatic calculations of mathematical operations, a term that used to refer to humans who performed the manual calculations of such operations. Today, the importance of this technology in large-scale transaction processing remains unparalleled. Large industries in both the public and private sectors, from government and banking to aviation and healthcare, are in constant need of faster large-scale mainframes with higher stability and reliability. Consequently, big irons continue to evolve, as they remain at the core of every IT infrastructure.

Inspired by Babbage

Howard Aiken was a graduate student at Harvard when he came up with the concept of a device that can automatically calculate differential equations, after encountering difficulties in solving mathematical physics problems in his research.[1] He envisioned a machine that could take in loads of mathematical inputs and produce precise and reliable results in a short time. After coming up with an initial design, he approached some manufacturers, but none were interested. Unabashed, Aiken explored other technological advances to improve his design. He eventually came upon Henry Babbage’s demonstration of his father’s Analytical Engine at Harvard, performed 70 years prior. Noticing the similarities between his design and that of Charles Babbage’s, Aiken studied Babbage’s work on the Analytical Engine and used his principles in the development of a new conceptual design. Aiken finished the design in 1937 and obtained the support of the Harvard faculty, who were impressed by his efforts. He presented his design to several manufacturers. Aiken eventually gained the nod from IBM in 1939 after Thomas Watson, then chairman of IBM, saw it as good publicity for the company and as an opportunity to showcase the company’s talents.[2]

Automatic Sequence Controlled Calculator

Construction of the machine started in 1939 at the IBM plant in Endicott, NY. The original design was composed of electromechanical components, such as switches, relays, rotating shafts, and clutches. A total of over 750,000 components, 500 miles of wires, and 3 million connections were used.[3] Input occurred through a 24-channel punched paper tape, two card readers, and a card punch, and the output was printed by two built-in typewriters.[4] The completed device occupied a whole room, weighing five tons and measuring 51 feet long, 8 feet high, and 2 feet deep. The device was enclosed in an elaborate casing designed by IBM’s industrial designer, Normal Bel Geddes. After five years and roughly $300,000 later, IBM shipped the enormous calculator to Harvard in February 1944. The device was originally called the Automatic Sequence Controlled Calculator (ASCC) by IBM. As the largest electromechanical calculator at the time, the ASCC could process addition or subtraction in 1 second, multiplication in 6 seconds, and division in 15.3 seconds. Furthermore, the device could compute logarithmic and trigonometric functions in just over a minute.[5] Because it is basically a calculator that can compute massive mathematical operations, the device was also called the ‘Harvard Calculator.’[6] It was only later, when there was a rift between Aiken and IBM, that Aiken began calling the device ‘Harvard Mark I,’ or simply, ‘Mark I.’

First Operators

Mark I was first operated by Harvard civilians under the direction of Robert Campbell, who ran a series of test runs after the device’s installation. In May 1944, the US Navy Bureau of Ships sent in its crew to operate the device, together with the technicians at Harvard. In 1946, Aiken and Grace Hopper published the machine’s instruction manual, A Manual of Operation for the Automatic Sequence Controlled Calculator, which documents the machine’s physical components, operation, maintenance, and instructions on how to program the machine. Because of its elaborate and detailed instructions, the manual also became the first computer programming textbook. The mathematical tables printed by Mark I from 1946-1950 were compiled in a series of books titled, Annals of the Computation Laboratory.

A Gigantic Military Aid

For the most part, Mark I was used to calculate and print mathematical tables that were used by the military in designing a wide range of military equipment, such as underwater detection systems, surveillance cameras, and radars. Mark I was also used to compute Bessel Functions in one of its longest-running projects, which some referred to as ‘Bessie.’ But perhaps its most notable contribution to the military was in the Manhattan Project, an undertaking that created the first nuclear weapons. John von Neumann, a Manhattan Project veteran, ran one of the first programs on Mark I while working on the implosion of atomic bombs.

The Mark I Controversy

The success of the Harvard Mark I success is not spared from its controversies. After the device’s launch in 1944, the Harvard News Office issued a press release claiming Aiken to be the sole inventor of the machine and disregarding the efforts of IBM engineers. Of the eight pages, only one paragraph was written about IBM’s contribution, with no mention of the company’s crucial role in the construction and development of the machine. Moreover, the release was issued without any consultation from IBM.[7] These deeply enraged Thomas Watson, who had personally approved Aiken’s project, and he reluctantly attended the dedication ceremony in August 1944. Though he was later appeased by Aiken, all future projects by Aiken were constructed without the help of IBM.

Leaving a Mark

The Harvard Mark I is a monumental invention in the history of computing. Mark I churned mathematical tables for 16 years, concluding its final computations in 1959. After Mark I, Aiken developed three more machines of its kind, which he named Mark II, Mark III, and Mark IV. Just like any other device, the development of its more advanced successors rendered Mark I technologically obsolete. Today, portions of the original machine are on display at the Harvard University Science Center, while some sections of the device went to IBM and the Smithsonian Institute.


[1] Collection of Historical Scientific Instruments. “The Mark I Computer at Harvard University” N.d., Accessed 12 Oct 2020

[2] Jeremy Norman. “Key Aspects of the Development of the Harvard Mark 1 and its Software by Howard Aiken and Grace Hopper”, History of Information, N.d., Accessed 12 Oct 2020

[3] Wikipedia. “Harvard Mark I”, N.d., Accessed 12 Oct 2020

[4] Britannica. “Harvard Mark I” N.d., 12 Oct 2020

[5] Wikipedia. “Harvard Mark I”, N.d., Accessed 12 Oct 2020

[6] Collection of Historical Scientific Instruments. “The Mark I Computer at Harvard University” N.d., Accessed 12 Oct 2020

[7] J.A.N. Lee. “Computer Pioneers”, IEEE Computer Society, N.d., 12 Oct 2020

About the author

Glynis Navarrete

Glynis Navarrete

A freelance blogger who loves to write about anything related to technology. Born and raised in the Philippines and worked in Singapore for eight years as Technical Support for a wide range of IT equipment. Took a dive into the world of freelancing and now enjoying doing what I’m passionate about while not losing touch with technology.