Chapter 3 The computer space 39
Nevertheless, the term is useful in stressing that the history of computer systems is not just a story of particular men discovering or building particular things, but of a somewhat more impersonal and widespread series of advances that have changed computer systems radically.
The generations are best defined solely in terms of logic technology: The first generation is that of vacuum tubes (1945 ~ 1958), the second generation is that of transistors (1958 ~ 1966), and the third generation is that of integrated circuits (1966~). In fact, current usage describes hybrid logic technology machines, such as the IBM System/360, as third generation, and so this extension must be included. What will be called fourth generation is yet to emerge; most likely it will be medium and large scale integrated circuits with possibly integrated circuit primary memory.
It is a measure of American industry's generally ahistorical view of things that the title of "first" generation has been allowed to be attached to a collection of machines which were some generations removed from the beginnings by any reasonable accounting. Mechanical and electromechanical computers existed prior to electronic ones. Furthermore, they were the functional equivalents of electronic computers and were realized to be such. They were also separated by a wide gap in performance and structure, both from each other and from vacuum tube machines. Thus, by reasonable reckoning, we are currently in the fifth generation of computers, not the third. But usage is now too well established to change.
Actually, it was not always viewed thus. Figure 1 reproduces a genealogical tree of the early computers prepared by the Na-
Fig. 1. The "family tree" of computer design. The remarkable growth of electronic computing systems in the Western world began primarily through government support of research and development in the universities. The need for data-processing facilities of increased capacity inspired further support for their development in both educational institutions and private industry. The current generation of computers is predominantly the result of development by private industry. The tree lists many of the machines developed in these ways. At the roots are the contributions of many existing technologies to the rapid growth from electromechanical to electronic systems. Some of the milestones are ENIAC (Electronic Numerical Integrator and Computer), the first electronic computer; EDVAC (Electronic Discrete Variable Automatic Computer), the first internally stored- program computer and first acoustic delay-line storage; MADM (Manchester Automatic Digital Machine), the first index registers (B lines) and first cathode-ray-tube electrostatic storage; MTC (Memory Test Computer), the first core-storage computer. (Courtesy of National Science Foundation.)