**The invention:** Early digital calculator designed to solve differential equations that was a forerunner of modern computers.

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**The people behind the invention:**

Howard H. Aiken (1900-1973), Harvard University professor and architect of the Mark I Clair D. Lake (1888-1958), a senior engineer at IBM Francis E. Hamilton (1898-1972), an IBM engineer Benjamin M. Durfee (1897-1980), an IBM engineer

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**The Human Computer**

The physical world can be described by means of mathematics. In principle, one can accurately describe nature down to the smallest detail. In practice, however, this is impossible except for the simplest of atoms. Over the years, physicists have had great success in creating simplified models of real physical processes whose behavior can be described by the branch of mathematics called “calculus.”

Calculus relates quantities that change over a period of time. The equations that relate such quantities are called “differential equations,” and they can be solved precisely in order to yield information about those quantities. Most natural phenomena, however, can be described only by differential equations that can be solved only approximately. These equations are solved by numerical means that involve performing a tremendous number of simple arithmetic operations (repeated additions and multiplications). It has been the dream of many scientists since the late 1700′s to find a way to automate the process of solving these equations.

In the early 1900′s, people who spent day after day performing the tedious operations that were required to solve differential equations were known as “computers.” During the two world wars, these human computers created ballistics tables by solving the differential equations that described the hurling of projectiles and the dropping of bombs from aircraft. The war effort was largely responsible for accelerating the push to automate the solution to these problems.

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**A Computational Behemoth**

The ten-year period from 1935 to 1945 can be considered the prehistory of the development of the digital computer. (In a digital computer, digits represent magnitudes of physical quantities. These digits can have only certain values.) Before this time, all machines for automatic calculation were either analog in nature (in which case, physical quantities such as current or voltage represent the numerical values of the equation and can vary in a continuous fashion) or were simplistic mechanical or electromechanical adding machines.

This was the situation that faced Howard Aiken. At the time, he was a graduate student working on his doctorate in physics. His dislike for the tremendous effort required to solve the differential equations used in his thesis drove him to propose, in the fall of 1937, constructing a machine that would automate the process. He proposed taking existing business machines that were commonly used in accounting firms and combining them into one machine that would be controlled by a series of instructions. One goal was to eliminate all manual intervention in the process in order to maximize the speed of the calculation.

Aiken’s proposal came to the attention of Thomas Watson, who was then the president of International Business Machines Corporation (IBM). At that time, IBM was a major supplier of business machines and did not see much of a future in such “specialized” machines. It was the pressure provided by the computational needs of the military in World War II that led IBM to invest in building automated calculators. In 1939, a contract was signed in which IBM agreed to use its resources (personnel, equipment, and finances) to build a machine for Howard Aiken and Harvard University.

IBM brought together a team of seasoned engineers to fashion a working device from Aiken’s sketchy ideas. Clair D. Lake, who was selected to manage the project, called on two talented engineers— Francis E. Hamilton and Benjamin M. Durfee—to assist him.

After four years of effort, which was interrupted at times by the demands of the war, a machine was constructed that worked remarkably well. Completed in January, 1943, at Endicott, New York, it was then disassembled and moved to Harvard University in Cam-

bridge, Massachusetts, where it was reassembled. Known as the IBM automatic sequence controlled calculator (ASCC), it began operation in the spring of 1944 and was formally dedicated and revealed to the public on August 7, 1944. Its name indicates the machine’s distinguishing feature: the ability to load automatically the instructions that control the sequence of the calculation. This capability was provided by punching holes, representing the instructions, in a long, ribbonlike paper tape that could be read by the machine.

Computers of that era were big, and the ASCC I was particularly impressive. It was 51 feet long by 8 feet tall, and it weighed 5 tons. It contained more than 750,000 parts, and when it was running, it sounded like a room filled with sewing machines. The ASCC later became known as the Harvard Mark I.

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**Impact**

Although this machine represented a significant technological achievement at the time and contributed ideas that would be used in subsequent machines, it was almost obsolete from the start. It was electromechanical, since it relied on relays, but it was built at the dawn of the electronic age. Fully electronic computers offered better reliability and faster speeds. Howard Aiken continued, without the help of IBM, to develop successors to the Mark I. Because he resisted using electronics, however, his machines did not significantly affect the direction of computer development.

For all its complexity, the Mark I operated reasonably well, first solving problems related to the war effort and then turning its attention to the more mundane tasks of producing specialized mathematical tables. It remained in operation at the Harvard Computational Laboratory until 1959, when it was retired and disassembled. Parts of this landmark computational tool are now kept at the sonian Institute.

See also BASIC programming language; Differential analyzer; Personal computer; Pocket calculator; UNIVAC computer.