It Began with Babbage (21 page)

Just as the numeric “digital style” of computing reached back to Victorian Britain so also did the “analog style.” The
doyen
of late Victorian British science, Scottish mathematical physicist William Thomson, Lord Kelvin (1824–1907), conceived, in 1876, the “harmonic analyzer” for solving equations that described tidal behavior.
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Kelvin's harmonic analyzer was never actually built. In any case, Bush, apparently unaware of Kelvin's ideas until much later, went his own way to build his differential analyzer.
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The principal computing unit in the differential analyzer was comprised of a set of six “integrators” for performing integration, the means by which differential equations would be solved. In addition, systems of gears performed the four arithmetic operations.
¹⁹
A differential equation to be solved for
y
as a function of
x
, say, would be prepared in the form of one or more integrals. An integrator would be supplied with values of
x
, the variable of integration, and
y
, the integrand, and would produce the value of ∫
ydx
. The input values would be translated into amounts of physical movements (linear displacements, angular rotations) of disks, wheels, gears, shafts, and styluses, although the output could also be printed out on a printer. The whole system was driven electrically by the main shaft rotated by an electric motor, with this shaft representing the independent variable
x
.
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Other than this, the machine's components and their interconnections were entirely mechanical.

In the words of Bush's biographer, the differential analyzer was an “imposing contraption” yet “brutish.”
²¹
Its operation would cause metal to “clank” with metal.
²²
Setting up
a problem for solution entailed disassembling the machine and reassembling it to set the linear and angular displacements of its mechanical components to represent the input values; various adjustments would be made to the components. More specifically, solving a particular set of differential equations involved the following steps:

Problem preparation
: The equation would be transformed into an integral form.
Determination of the interconnections of the units
: This was undertaken to solve the equation.
Manual connection of the physical units
: This entailed placing gear wheels, addition units, and shafts into positions and tightening them manually.
Problem running
: This necessitated the setup of the initial conditions corresponding to the initial values of the variables.

Typically, a problem setup would take 2 or 3 days.
²³
To obviate some of these problems, in a second version of the MIT differential analyzer built by Bush and his student (and, later, colleague) Samuel Caldwell (1904–1960), and completed in 1942, transmission of the values of variables through shafts and gears was replaced by electrical methods. Very soon thereafter, circumstances would overtake the differential analyzer completely.

During the 1930s, Bush's differential analyzer attracted a great deal of attention. It was a “smashing success” according to Bush's biographer.
²⁴
As we have noted, the Aberdeen Proving Ground acquired its own copy of the machine in 1935. Early during the 1940s, the Moore School of Electrical Engineering of the University of Pennsylvania in Philadelphia took charge of this machine on behalf of the BRL and started a program to train people in ballistic computation—especially women who had science degrees.
²⁵
In September 1942, Goldstine was put in charge of this operation at the Moore School,
²⁶
and thus was established the nexus between the Moore School of Electrical Engineering and the BRL—more fatefully, between the Moore School and computers. Through the exigencies and happenstance of wartime decisions, the Moore School planted for itself a secure place in the history of computing.

After America entered World War II, the school became a center for computing firing tables.
²⁷
The differential analyzer was fully occupied. But then, as Burks recalled, a certain John Mauchly (1903–1980) suggested to Goldstine that these firing tables could be compiled must faster with electronic devices. On Goldstine's request, Mauchly and two colleagues, Presper Eckert (1919–1995) and John Brainerd (1904–1988), wrote a proposal for an “electronic differential analyzer” in April 1943, for which it was calculated that this machine would compute ballistic trajectories 10 times faster than the electromechanical differential analyzer. The proposal was submitted on behalf of the Moore School to the BRL.
²⁸

Thus, two new protagonists enter this story, Mauchly and Eckert, whose names are forever twinned, as are other scientific “couples” in the annals of science, such as Cockcroft and Walton in atomic physics, Watson and Crick in molecular biology, Yang and Lee in theoretical physics, and Hardy and Littlewood in pure mathematics.

Mauchly was a physicist who, at the time the war broke out, was on the physics faculty at Ursinus College, a liberal arts college just outside Philadelphia, and a person with a long-standing interest in automatic computing. Eckert (no relation to Wallace Eckert [see
Chapter 5
, Section V]) was a graduate student in electrical engineering, “undoubtedly the best electronic engineer in the Moore School.”
²⁹
The third author of the proposal, Brainerd, was a professor of electrical engineering at the Moore School, with a deep interest in using the differential analyzer. Goldstine persuaded the powers that be in the BRL to finance the project, which they did. The electronic differential analyzer later became the ENIAC.
³⁰

So began a new chapter of this story, but a chapter embedded in a tangled web of means and ends, of people and personalities, of insights and ideas, of controversies.

This part of the story must begin, in 1939/1940, in Ames, Iowa, with another pair of collaborators: John Vincent Atanasoff (1903–1995) and Clifford Berry (1918–1963). The former was on the faculty of the physics department at Iowa State College (later Iowa State University); the latter, a just-graduated electrical engineer and Atanasoff's graduate student in physics. An unpublished memorandum authored by Atanasoff in 1940 spoke of the occurrence of systems of linear simultaneous algebraic equations in many fields of physics, technology, and statistics, and the necessity of solving such equations speedily and accurately.
³¹

The time to solve such equations of even moderate complexity manually—by a (human) computer
³²
—was prohibitively large; equations containing a very large number of “unknowns” (that is, variables) were well nigh unapproachable. Like almost all his predecessors who have appeared in this story, Atanasoff was dissatisfied with the status quo. He sought help from automata. Some 7 years earlier, Atanasoff wrote in a 1940 memorandum that he had begun to investigate the possibility of automating the solution to such problems,
³³
although it was only in 1939 that he began an actual project to build a computer for solving linear simultaneous equations with Berry as assistant. This machine was completed in 1942. Later, it would be called the
Atanasoff–Berry Computer
(ABC).
³⁴

However, Atanasoff's approach differed in some respects from his contemporaries. He considered, then discarded, punched-card tabulators because of their insufficient computational power. He dwelled on binary computation and concluded that it was superior to other number systems. He then considered the design of the actual mechanisms to use and decided, first, that he would use small electrical condensers (capacitors, in
present-centered language) to represent the binary digits 0 and 1—a positive charge representing 1 and a negative charge, 0.
³⁵
As for the computing unit, it would be made of vacuum tubes.
³⁶

The ABC became an operational electronic digital computer in 1942, capable of performing the task (up to some limit) it was designed to do. Later, it would be acknowledged as the world's
first
operational electronic digital computer, preceding the Colossus. More important, for this story, it embodied a number of noteworthy innovations.

First, as noted, vacuum tube circuits were used for the computational (arithmetic) units. By the mid 1930s, the use of vacuum tubes, resisters, and capacitors in radios was well established. However, these circuits operated in analog or continuous mode. Digital circuit elements such as flip-flops, counters, and simple switching circuits had also been implemented, but the digital use of vacuum tubes for building such circuits was quite rare.
³⁷

Second, memory was implemented in the form of electrical condensers (capacitors) mounted on two rotating Bakelite drums 8 inches in diameter and 11 inches long. A positive charge on a condenser represented 1; a negative charge, 0. Each drum could store 30 50-bit numbers. As the drum rotated, these numbers could be read, processed, and replaced serially. The two drums were mounted on the same axle so that they could operate synchronously.

Third, the ABC was designed to solve simultaneous linear equations by the widely used method of Gaussian elimination. For this purpose, the coefficients in the equations were read from punched cards onto the drums. By a succession of binary additions, subtractions, and shifting binary numbers right or left, the computation would be performed.

Fourth, the computation units consisted of 30 add–subtract units that took numbers from the storage drums and performed the adds or subtracts in parallel. Circuits were also available for shifting binary numbers. There were no separate circuits for multiplication or division.

Fifth, internally, the ABC was a binary machine. However, input data fed to the computer through punched cards were in decimal form, and so decimal-to-binary conversions were done before numbers were stored on the drums; conversely, binary-to-decimal conversions were performed before outputting results in decimal form. These outputs were displayed on dials.
³⁸

Sixth, and last, intermediate results were stored in binary form on cards. For this purpose, Atanasoff recorded binary digits on the card with electric sparks that carbonized the card at those locations. These binary digits could then be read by applying a voltage to the card because a carbonized spot provided less resistance to the reading voltage than a spot that had not been carbonized.
³⁹

When the ABC was completed, all components worked well except the electric spark mechanism, which would fail occasionally. Because of this, the ABC could solve small sets of equations correctly, but not large ones because the latter demanded very large numbers of binary digits to be both recorded as intermediate results and then read. It was
because of this weakness that the ABC was almost (but only almost) fully operational. Atanasoff and Berry never resolved this problem. In fall 1942, they were both called into war research. Neither returned to Iowa State College after the war, and the ABC was eventually dismantled.
⁴⁰
Yet, as would be acknowledged later, in designing and building the ABC, Atanasoff and Berry demonstrated the viability of electronic switching circuits across a range of units desirable in a computer—to perform arithmetic operations, base conversions, and control functions.

Here was a science of the artificial in action (see Prologue, Section VI): a design for a particular computer representing a theory of the machine, the purpose of which was the solution of linear algebraic equations; a theory that embedded the logical organization of the computer (its architecture) and the physical characteristics of its parts; and an implementation that afforded the crucial experiment to test whether a computer built according to the design would serve its intended purpose. The design constituted a theory of an
individual
machine (see Prologue, Section VI). The implementation constituted an experiment about such a singular theory, and the implementation revealed not only the broad validity of the design-as-theory, but also where the theory–experiment ensemble failed—in the fact that the machine was limited to small systems of equations. The next logical step would be either to modify the design or the implementation to eliminate the error. But, as noted, this never happened because of the exigencies of war.

Atanasoff also realized that the ABC could do more than solve systems of linear equations. Becoming aware, in spring 1941, of the improved differential analyzer being built by Bush and Caldwell, he realized that his machine could also be used to solve differential equations by way of numeric integration.
⁴¹

In June 1941, Mauchly, then a physics faculty member at Ursinus College, visited Atanasoff in Ames, Iowa, to learn about the ABC, which was still a work in progress at that time. The two had met at a scientific conference in December 1940, at which time Mauchly had come to know of Atanasoff's computer project. In fact, even before his visit to Ames, Mauchly was told by Atanasoff, in a letter written in May 1941, of the idea of using the ABC to solve differential equations.
⁴²

During the 4 days Mauchly stayed in Ames, he had extensive opportunity to examine the ABC and hold discussions with his host about electronic computers.
⁴³
Mauchly also read, and made notes from, Atanasoff's memorandum of August 1940.
⁴⁴

In September 1941, Mauchly wrote to Atanasoff of his “hope” to “outdo the analyzer electronically.” He mentioned some “different ideas” that had occurred to him, some of which combined Atanasoff's ideas with others, some quite different.
⁴⁵
More pointedly, he asked Atanasoff whether the latter would object to his (Mauchly's) incorporating some of the ABC's features into his own design.
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