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It Operations Support A block diagram of the Babbage analytical engine is shown in Figure 1.13. The mill was capable of selecting one of four arithmetic operations, and of testing the sign of a number with a different program branch specified for each result. The sequence of operation was specified by instructions on the operation cards. The operation cards could be advanced or reversed as a means of implementing a sort of ‘‘goto’’ instruction. The second set of cards, known as variable cards, were to be used to specify particular memory locations for the data involved in the calculations.


It Operations Support Babbage envisioned a memory of one thousand 50-digit decimal numbers. Each digit was to be stored using a ten-toothed gear known as a counter wheel. Although the analytical engine was never completed, it should be apparent to you that it contains all the essential elements of today’s computers. At approximately the same time, another English mathematician, George Boole, developed the binary theory of logic that bears his name, Boolean logic. He also recognized the relationship between binary arithmetic and Boolean logic that makes possible the circuitry that implements the modern electronic computer

It Operations Support In the late 1930s and early 1940s, several different groups of researchers independently developed versions of the modern electronic computer. The Mark I, built in 1937 by Howard H. Aiken and associates at Harvard University with help and funding from IBM, used thousands of relays; relays are mechanical binary switches controlled by electrical currents, familiar to you perhaps as the clicking devices that control operations in tape cassette players and telephone answering machines. Although binary relays were used for computation, the fundamental design was decimal. Storage consisted of seventy-two 23-digit decimal numbers, stored on counter wheels. An additional counter wheel digit held the sign, using the digit 0 for plus and 9 for minus. The design appears to be based directly on Babbage’s original concepts and use of mechanical calculator parts from IBM accounting machines. A similar electromechanical computer was designed and built by Conrad Zuse in Germany at about the same time.

It Operations Support The first totally electronic digital computer was apparently devised by John V. Atanasoff, a physicist at Iowa State College, in 1937. The machine was built in 1939 by Atanasoff and a graduate student, Clifford Berry, using electronic vacuum tubes as the switching components. The machine was known as ABC, for Atanasoff-Berry Computer. It is claimed that Atanasoff worked out the original details as he drove restlessly late one winter night from his house in Iowa to a bar in neighboring Illinois. The machine was not intended as a general-purpose computer, but was built to solve physics equations that Atanasoff was working on at the time. There is some doubt as to whether the machine ever worked completely

ABC was a binary-based machine, just like today’s computers. It consisted of an arithmetic/logic unit with thirty units that could do addition and subtraction, a rotating drum memory that held thirty binary numbers of 50 digits each, and punched card input. Each punched card held five 15-digit decimal numbers. These numbers were converted to binary as they entered the machine. Despite its limitations, ABC was an important pathmark that led to later significant advances in computer design. It is only recently that Atanasoff has begun to receive recognition for his achievement

It Operations Support Much of the effort that culminated in a successful general-purpose computer architecture resulted from a wartime need for the solution to difficult mathematical formulas related to ballistic missile trajectories and other World War II research. The ENIAC (for Electronic Numerical Integrator and Computer, believe it or not) is generally considered to be the first all-electronic digital computer. It was designed and built between 1943 and 1946 by John W. Mauchly and J. Presper Eckert at the University of Pennsylvania, using the concepts that Mauchly had seen in Atanasoff’s machine, although this was not publicly known at the time.

It Operations Support ENIAC had very limited storage capability, with only twenty locations each capable of holding a 10-digit decimal number. An additional one hundred numbers could be stored in read-only memory. Calculations were performed using decimal arithmetic. Ten electronic vacuum tube binary switches were used for each digit, with only one switch in the ‘‘ON’’ position to represent the value of the digit. Input and output used punched cards. The system could also provide printed output.

It Operations Support Programs could not be stored internally, but were hard wired with external ‘‘patch panels’’ and toggle switches. It took many hours to change programs, and, of course, debugging was a nightmare. Nonetheless, ENIAC was an important machine, some say the most important machine, especially since it led directly to the development of the UNIVAC I, the first commercially available computer, in 1951.

It Operations Support ENIAC contained eighteen thousand vacuum tubes, occupied a floor space of more than fifteen thousand square feet, and weighed more than thirty tons. A photograph of ENIAC, taken from The New York Times of February 15, 1946, is shown in Figure 1.14. Even in its day, ENIAC was recognized as an important achievement. ENIAC operated successfully until 1955, when it was dismantled, but not destroyed. Parts of the computer can be seen at the Smithsonian Institute, at the U.S. Military Academy at West Point, at the Moore School of the University of Pennsylvania, and at the University of Michigan

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