This machine does thousands of calculating steps, one after another, according to a scheme fixed ahead of time. This property is what gives the machine its name: automatic, since the individual operations are automatic, once the punched tape fixing the chain of operations has been put on the machine, and sequence-controlled, since control over the sequence of its operations has been built into the machine.
ORIGIN AND DEVELOPMENT
More than a hundred years ago, an English mathematician and actuary, Charles Babbage (1792-1871), designed a machine—or engine as he called it—that would carry out the sequences of mathematical operations. In the 1830’s he received a government grant to build an analytical engine whereby long chains of calculations could be performed. But he was unsuccessful, because the refined physical devices necessary for quantities of digital calculation were not yet developed. Only in the 1930’s did these physical devices become sufficiently versatile and reliable for a calculator of hundreds of thousands of parts to be successful.
The Automatic Sequence-Controlled Calculator at Harvard was largely the concept of Professor Howard H. Aiken of Harvard. It was built through a partnership of efforts, ideas, and engineering between him and the International Business Machines Corporation, in the years 1937 to 1944. The calculator was a gift from IBM to Harvard University. Some very useful additional control units, named the Subsidiary Sequence Mechanism, were built at the Harvard Computation Laboratory in 1947 and joined to the machine.
Fig. 1. Scheme of Harvard IBM Automatic
Sequence-Controlled Calculator.
GENERAL ORGANIZATION
The machine ([see Fig. 1]) is about 50 feet long, 8 feet high, and about 2 feet wide. It consists of 22 panels; 17 of them are set in a straight line, and the last 5 are at the rear of the machine. In the scheme of the machine shown in [Fig. 1], the details you would see in a photograph have been left out. Instead you see the sections of the machine that are important because of what they do: input, memory, control, and output. Why do we not see a section labeled “computer”? Because in this mechanical brain the computing part of the machine is closely joined to the memory: every storage register can add and subtract. We shall soon discuss these sections of the machine more fully.
PHYSICAL DEVICES
Now in order for any brain to work, physical devices must be used. For example, in the human body, a nerve is the physical device that carries information from one part of the body to another. In the Harvard machine, an insulated wire is the physical device that carries information from one part of the machine to another. One side of every panel in the Harvard machine is heavily laden with a great network of wires. Between the panels, you can see in many places cables as thick as your arm and containing hundreds of wires. More than 500 miles of wire are used.