1. The First Generation:Vacuum Tubes


The ENIAC (Electronic Numerical Integrator And Computer), designed and constructed at the University of Pennsylvania, was the world’s first generalpurpose electronic digital computer.The project was a response to U.S. needs during World War II.The Army’s Ballistics Research Laboratory (BRL), an agency responsible for developing range and trajectory tables for new weapons, was having difficulty supplying these tables accurately and within a reasonable time frame. Without these firing tables, the new weapons and artillery were useless to gunners. The BRL
employed more than 200 people who, using desktop calculators, solved the necessary ballistics equations. Preparation of the tables for a single weapon would take one person many hours, even days.

John Mauchly, a professor of electrical engineering at the University of  Pennsylvania, and John Eckert, one of his graduate students, proposed to build a general-purpose computer using vacuum tubes for the BRL’s application. In 1943, the Army accepted this proposal, and work began on the ENIAC. The resulting machine was enormous, weighing 30 tons, occupying 1500 square feet of floor space, and containing more than 18,000 vacuum tubes. When operating, it consumed 140 kilowatts of power. It was also substantially faster than any electromechanical
computer, capable of 5000 additions per second.

The ENIAC was completed in 1946, too late to be used in the war effort. Instead, its first task was to perform a series of complex calculations that were used to help determine the feasibility of the hydrogen bomb. The use of the ENIAC for a purpose other than that for which it was built demonstrated its general-purpose nature.The ENIAC continued to operate under BRL management until 1955, whenit was disassembled.


The task of entering and altering programs for the ENIAC was extremely tedious. The programming process could be facilitated if the program could be represented in a form suitable for storing in memory alongside the data. Then, a computer could get its instructions by reading them from memory, and a program could be set or altered by setting the values of a portion of memory. This idea, known as the stored-program concept, is usually attributed to the
ENIAC designers, most notably the mathematician John von Neumann, who was a consultant on the ENIAC project.Alan Turing developed the idea at about the same time. The first publication of the idea was in a 1945 proposal by von Neumann for a new computer, the EDVAC (Electronic Discrete Variable Computer).
In 1946, von Neumann and his colleagues began the design of a new storedprogram computer, referred to as the IAS computer, at the Princeton Institute for Advanced Studies.The IAS computer, although not completed until 1952, is the prototype of all subsequent general-purpose computers.


The 1950s saw the birth of the computer industry with two companies, Sperry and IBM, dominating the marketplace.In 1947, Eckert and Mauchly formed the Eckert-Mauchly Computer Corporation to manufacture computers commercially. Their first successful machine was the UNIVAC I (Universal Automatic Computer), which was commissioned by the Bureau of the Census for the 1950 calculations.The Eckert-Mauchly Computer Corporation
became part of the UNIVAC division of Sperry-Rand Corporation, which went on to build a series of successor machines.
The UNIVAC I was the first successful commercial computer. It was intended for both scientific and commercial applications. The first paper describing the system listed matrix algebraic computations, statistical problems, premium billings for a life insurance company, and logistical problems as a sample of the tasks it could


2. The Second Generation:Transistors

The first major change in the electronic computer came with the replacement of the vacuum tube by the transistor. The transistor is smaller, cheaper, and dissipates less heat than a vacuum tube but can be used in the same way as a vacuum tube to construct computers. Unlike the vacuum tube, which requires wires, metal plates, a glass
capsule, and a vacuum, the transistor is a solid-state device, made from silicon. The transistor was invented at Bell Labs in 1947 and by the 1950s had launched an electronic revolution. It was not until the late 1950s, however, that fully transistorized computers were commercially available. IBM again was not the first company to deliver the new technology. NCR and, more successfully, RCA were the front-runners with some small transistor machines. IBM followed shortly with the 7000 series.


3. The Third Generation: Integrated Circuits

A single, self-contained transistor is called a discrete component. Throughout the 1950s and early 1960s, electronic equipment was composed largely of discrete components— transistors, resistors, capacitors, and so on. Discrete components were manufactured separately, packaged in their own containers, and soldered or wired together onto masonite-like circuit boards, which were then installed in computers, oscilloscopes, and other electronic equipment.Whenever an electronic device called for a transistor, a little tube of metal containing a pinhead-sized piece of silicon had to be soldered to a circuit board. The entire manufacturing process, from transistor to circuit board, was expensive and cumbersome. These facts of life were beginning to create problems in the computer industry. Early second-generation computers contained about 10,000 transistors. This figure grew to the hundreds of thousands, making the manufacture of newer, more powerful machines increasingly difficult. In 1958 came the achievement that revolutionized electronics and started the era of microelectronics: the invention of the integrated circuit. It is the integrated circuit that defines the third generation of computers.


4. Later Generations

Beyond the third generation there is less general agreement on defining generations of computers. Table 2.2 suggests that there have been a number of later generations, based on advances in integrated circuit technology. With the introduction of large scale integration (LSI), more than 1000 components can be placed on a single integrated
circuit chip. Very-large-scale integration (VLSI) achieved more than 10,000 components per chip, while current ultra-large-scale integration (ULSI) chips can contain more than one million components. With the rapid pace of technology, the high rate of introduction of new products, and the importance of software and communications as well as hardware, the classification by generation becomes less clear and less meaningful. It could be said that the commercial application of new developments resulted in a major change in the early 1970s and that the results of these changes are still being worked out. In this section, we mention two of the most important of these results.

SEMICONDUCTOR MEMORY : The first application of integrated circuit technology to computers was construction of the processor (the control unit and the arithmetic and logic unit) out of integrated circuit chips. But it was also found that this same technology could be used to construct memories.

MICROPROCESSORS : Just as the density of elements on memory chips has continued to rise, so has the density of elements on processor chips.As time went on, more and more elements were placed on each chip, so that fewer and fewer chips were needed to construct a single computer processor.
A breakthrough was achieved in 1971, when Intel developed its 4004.The 4004 was the first chip to contain all of the components of a CPU on a single chip:The microprocessor was born.

The next major step in the evolution of the microprocessor was the introduction in 1972 of the Intel 8008. This was the first 8-bit microprocessor and was almost twice as complex as the 4004. Neither of these steps was to have the impact of the next major event: the introduction in 1974 of the Intel 8080. This was the first general-purpose microprocessor. Whereas the 4004 and the 8008 had been designed for specific applications, the 8080 was designed to be the CPU of a general-purpose microcomputer. Like the 8008, the 8080 is an 8-bit microprocessor. The 8080, however, is faster, has a richer instruction set, and has a large addressing capability.


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