HISTORY OF COMPUTERS
Historically, the most important early computing instrument is the abacus, which has been known and widely used for more than 2,000 years. Another computing instrument, the astrolabe, was also in use about 2,000 years ago for navigation.
Blaise Pascal is widely credited with building the first "digital calculating machine" in 1642. It performed only additions of numbers entered by means of dials and was intended to help Pascal's father, who was a tax collector. In 1671, Gottfried Wilhelm von Leibniz invented a computer that was built in 1694; it could add and, by successive adding and shifting, multiply. Leibniz invented a special "stepped gear" mechanism for introducing the addend digits, and this mechanism is still in use. The prototypes built by Leibniz and Pascal were not widely used but remained curiosities until more than a century later, when Tomas of Colmar (Charles Xavier Thomas) developed (1820) the first commercially successful mechanical calculator that could add, subtract, multiply, and divide. A succession of improved "desk-top" mechanical calculators by various inventors followed, so that by about 1890 the available built-in operations included accumulation of partial results, storage and reintroduction of past results, and printing of results, each requiring manual initiation. These improvements were made primarily to suit commercial users, with little attention given to the needs of science.
While Tomas of Colmar was developing the desktop calculator Charles Babbage initiated a series of very remarkable developments in computers in Cambridge, England. Babbage realized (1812) that many long computations, especially those needed to prepare mathematical tables, consisted of routine operations that were regularly repeated; from this he surmised that it ought to be possible to do these operations automatically. He began to design an automatic mechanical calculating machine, which he called a "difference engine," and by 1822 he had built a small working model for demonstration. With financial help from the British government, Babbage started construction of a full-scale difference engine in 1823. It was intended to be steam-powered; fully automatic, even to the printing of the resulting tables; and commanded by a fixed instruction program.
The difference engine, although of limited flexibility and applicability, was conceptually a great advance. Babbage continued work on it for 10 years, but in 1833 he lost interest because he had a "better idea" the construction of what today would be described as a general-purpose, fully program-controlled, automatic mechanical digital computer. Babbage called his machine an "analytical engine"; the characteristics aimed at by this design show true prescience, although this could not be fully appreciated until more than a century later. The plans for the analytical engine specified a parallel decimal computer operating on numbers (words) of 50 decimal digits and provided with a storage capacity (memory) of 1,000 such numbers. Built-in operations were to include everything that a modern general-purpose computer would need, even the all-important "conditional control transfer" capability, which would allow instructions to be executed in any order, not just in numerical sequence. The analytical engine was to use punched cards (similar to those used on a Jacquard loom), which were to be read into the machine from any of several reading stations. It was designed to operate automatically, by steam power, with only one attendant.
Babbage's computers were never completed. Various reasons are advanced for his failure, most frequently the lack of precision machining techniques at the time. Another conjecture is that Babbage was working on the solution of a problem that few people in 1840 urgently needed to solve.
After Babbage there was a temporary loss of interest in automatic digital computers. Between 1850 and 1900 great advances were made in mathematical physics, and it came to be understood that most observable dynamic phenomena could be characterized by differential equations, so that ready means for their solution and for the solution of other problems of calculus would be helpful. Moreover, from a practical standpoint, the availability of steam power caused manufacturing, transportation, and commerce to thrive and led to a period of great engineering achievement. The designing of railroads and the construction of steamships, textile mills, and bridges required differential calculus to determine such quantities as centers of gravity, centers of buoyancy, moments of inertia, and stress distributions; even the evaluation of the power output of a steam engine required practical mathematical integration. A strong need thus developed for a machine that could rapidly perform many repetitive calculations.
A step toward automated computation was the introduction of punched cards, which were first successfully used in connection with computing in 1890 by Herman Hollerith and James Powers, working for the U.S. Census Bureau. They developed devices that could automatically read the information that had been punched into cards, without human intermediation. Reading errors were consequently greatly reduced, workflow was increased, and, more important, stacks of punched cards could be used as an accessible memory store of almost unlimited capacity; furthermore, different problems could be stored on different batches of cards and worked on as needed.
These advantages were noted by commercial interests and soon led to the development of improved punch-card business-machine systems by International Business Machines (IBM), Remington-Rand, Burroughs, and other corporations. These systems used electromechanical devices, in which electrical power provided mechanical motion such as for turning the wheels of an adding machine. Such systems soon included features to feed in automatically a specified number of cards from a "read-in" station; perform such operations as addition, multiplication, and sorting; and feed out cards punched with results. The machines were slow, typically processing from 50 to 250 cards per minute, with each card holding up to 80 decimal numbers. At the time, however, punched cards were an enormous step forward.
Automatic Digital Computers
By the late 1930s punched-card machine techniques had become well established and reliable, and several research groups strove to build automatic digital computers. An IBM team led by Howard Hathaway Aiken built one promising machine, constructed of standard electromechanical parts. Aiken's machine, called the Harvard Mark I, handled 23-decimal-place numbers (words) and could perform all four arithmetic operations. Moreover, it had special built-in programs, or subroutines, to handle logarithms and trigonometric functions. The Mark I was originally controlled from prepunched paper tape without provision for reversal, so that automatic "transfer of control" instructions could not be programmed. Output was by cardpunch and electric typewriter. Although the Mark I used IBM rotating counter wheels as key components in addition to electromagnetic relays, the machine was classified as a relay computer. It was slow, requiring 3 to 5 seconds for a multiplication, but it was fully automatic and could complete long computations. Mark I was the first of a series of computers designed and built under Aiken's direction.
Electronic Digital Computers
The outbreak of World War II produced a desperate need for computing capability, especially for the military. New weapons systems were produced for which trajectory tables and other essential data were lacking. In 1942, J. Presper Eckert, John W. Mauchly, and their associates at the Moore School of Electrical Engineering of the University of Pennsylvania decided to build a high-speed electronic computer to do the job. This machine became known as ENIAC, for Electronic Numerical Integrator and Computer (or Calculator). The size of its numerical word was 10 decimal digits, and it could multiply two such numbers at the rate of 300 products per second, by finding the value of each product from a multiplication table stored in its memory. Although difficult to operate, ENIAC was still many times faster than the previous generation of relay computers.
ENIAC used 18,000 standard vacuum tubes, occupied 167.3 m6 (1,800 ft6) of floor space and consumed about 180,000 watts of electrical power. It had punched-card input and output and arithmetically had 1 multiplier, 1 divider square rooter, and 20 adders employing decimal "ring counters," which served as adders and also as quick-access (0.0002 seconds) read-write register storage. The executable instructions composing a program were embodied in the separate units of ENIAC, which were plugged together to form a route through the machine for the flow of computations. These connections had to be redone for each different problem, together with presetting function tables and switches. This "wire-your-own" instruction technique was inconvenient, and only with some license could ENIAC be considered programmable; it was, however, efficient in handling the particular programs for which it had been designed. ENIAC is generally acknowledged to be the first successful high-speed electronic digital computer (EDC) and was productively used from 1946 to 1955. A controversy developed in 1971, however, over the patent ability of ENIAC's basic digital concepts, the claim being made that another U.S. physicist, John V. Atanasoff, had already used the same ideas in a simpler vacuum-tube device he built in the 1930s at Iowa State College. In 1973 the court found in favor of the company using the Atanasoff claim.
The Modern "Stored Program" EDC
Intrigued by the success of ENIAC, the mathematician John von Neumann undertook (1945) a theoretical study of computation that demonstrated that a computer could have a very simple, fixed physical structure and yet be able to execute any kind of computation effectively by means of proper programmed control without the need for any changes in hardware. Von Neumann contributed a new understanding of how practical fast computers should be organized and built; these ideas, often referred to as the stored-program technique, became fundamental for future generations of high-speed digital computers.
The stored-program technique involves many features of computer design and function besides the one named; in combination, these features make very-high-speed operation feasible. Details cannot be given here, but considering what 1,000 arithmetic operations per second imply may provide a glimpse. If each instruction in a job program were used only once in consecutive order, no human programmer could generate enough instructions to keep the computer busy. Arrangements must be made, therefore, for parts of the job program called subroutines to be used repeatedly in a manner that depends on how the computation progresses. Also, it would clearly be helpful if instructions could be altered as needed during a computation to make them behave differently. Von Neumann met these two needs by providing a special type of machine instruction called conditional control transfer who permitted the program sequence to be interrupted and reinitiated at any point and by storing all instruction programs together with data in the same memory unit, so that, when desired, instructions could be arithmetically modified in the same way as data.
Computing and programming became faster, more flexible, and more efficient, with the instructions in subroutines performing far more computational work. Frequently used subroutines did not have to be reprogrammed for each new problem but could be kept intact in "libraries" and read into memory when needed. Thus, much of a given program could be assembled from the subroutine library. The all-purpose computer memory became the assembly place in which parts of a long computation were stored, worked on piecewise, and assembled to form the final results. The computer control served as an errand runner for the overall process. As soon as the advantages of these techniques became clear, the techniques became standard practice.
The first generation of modern programmed electronic computers to take advantage of these improvements appeared in 1947. This group included computers using random access memory (RAM), which is a memory designed to give almost constant access to any particular piece of information. These machines had punched card or punched-tape input and output devices and RAMs of 1,000-word capacity with an access time of 0.5 microseconds (0.5? 10¦ sec); some of them could perform multiplications in 2 to 4 microseconds. Physically, they were much more compact than ENIAC: some were about the size of a grand piano and required 2,500 small electron tubes, far fewer than required by the earlier machines. The first-generation stored-program computers required considerable maintenance, attained perhaps 70% to 80% reliable operation, and were used for 8 to 12 years. Typically, they were programmed directly in machine language, although by the mid-1950s progress had been made in aspects of advanced programming. These machines included EDVAC and UNIVAC, the first commercially available computers.
Advances in the 1950s
Early in the 1950s two important engineering discoveries changed the image of the field, from one of fast but often unreliable hardware to an image of relatively high reliability and even greater capability. These discoveries were the magnetic-core memory and the transistor-circuit element.
These new technical discoveries rapidly found their way into new models of digital computers; RAM capacities increased from 8,000 to 64,000 words in commercially available machines by the early 1960s, with access times of 2 or 3 microseconds. These machines were very expensive to purchase or to rent and were especially expensive to operate because of the cost of expanding programming. Such computers were typically found in large computer centers operated by industry, government, and private laboratories staffed with many programmers and support personnel. This situation led to modes of operation enabling the sharing of the high capability available; one such mode is batch processing, in which problems are prepared and then held ready for computation on a relatively inexpensive storage medium, such as magnetic drums, magnetic-disk packs, or magnetic tapes. When the computer finishes with a problem, it typically "dumps" the whole problem program and results on one of these peripheral storage units and takes in a new problem. Another mode of use for fast, powerful machines is called time-sharing. In time-sharing the computer processes many waiting jobs in such rapid succession that each job progresses as quickly as if the other jobs did not exist, thus keeping each customer satisfied. Such operating modes require elaborate "executive" programs to attend to the administration of the various tasks.
Advances in the 1960s
In the 1960s efforts to design and develop the fastest possible computers with the greatest capacity reached a turning point with the completion of the LARC machine for Livermore Radiation Laboratories of the University of California by the Sperry-Rand Corporation, and the Stretch computer by IBM. The LARC had a core memory of 98,000 words and multiplied in 10 microseconds. Stretch was provided with several ranks of memory having slower access for the ranks of greater capacity, the fastest access time being less than 1 microsecond and the total capacity about 100 million words.
During this period the major computer manufacturers began to offer a range of computer capabilities and costs, as well as various peripheral equipment such input means as consoles and card feeders; such output means as page printers, cathode-ray-tube displays, and graphing devices; and optional magnetic-tape and magnetic-disk file storage. These found wide use in business for such applications as accounting, payroll, inventory control, ordering supplies, and billing. Central processing units (CPUs) for such purposes did not need to be very fast arithmetically and were primarily used to access large amounts of records on file, keeping these up to date. Most computer systems were delivered for the more modest applications, such as in hospitals for keeping track of patient records, medications, and treatments given. They are also used in automated library systems, such as MEDLARS, the National Medical Library retrieval system, and in the Chemical Abstracts system, where computer records now on file cover nearly all known chemical compounds.
The trend during the 1970s was, to some extent, away from extremely powerful, centralized computational centers and toward a broader range of applications for less-costly computer systems. Most continuous-process manufacturing, such as petroleum refining and electrical-power distribution systems, now use computers of relatively modest capability for controlling and regulating their activities. In the 1960s the programming of applications problems was an obstacle to the self-sufficiency of moderate-size on-site computer installations, but great advances in applications programming languages are removing these obstacles. Applications languages are now available for controlling a great range of manufacturing processes, for computer operation of machine tools, and for many other tasks.
Moreover, a revolution in computer hardware came about that involved miniaturization of computer-logic circuitry and of component manufacture by large-scale integration, or LSI, techniques. In the 1950s it was realized that "scaling down" the size of electronic digital computer circuits and parts would increase speed and efficiency and thereby improve performance if only manufacturing methods were available to do this. About 1960, photo printing of conductive circuit boards to eliminate wiring became highly developed. It then became possible to build resistors and capacitors into the circuitry by photographic means (see printed circuit).
In the 1970s vacuum deposition of transistors became common, and entire assemblies, such as adders, shifting registers, and counters, became available on tiny "chips." During this decade many companies, some new to the computer field, introduced programmable minicomputers supplied with software packages. The size-reduction trend continued with the introduction of personal computers, which are programmable machines small enough and inexpensive enough to be purchased and used by individuals (see computer, personal). Many companies, such as Apple Computer and Radio Shack, introduced very successful personal computers. Augmented in part by a fad in computer, or video, games, development of these small computers expanded rapidly.
In the 1980s, very large-scale integration (VLSI), in which hundreds of thousands of transistors are placed on a single chip, became increasingly common. During that decade the Japanese government announced a massive plan to design and build a new generation the so-called fifth generation of supercomputers that would employ new technologies in very large-scale integration. This project, however, was abandoned by the early 1990s (see artificial intelligence). The enormous success of the personal computer and resultant advances in microprocessor technology initiated a process of attrition among giants of the computer industry. That is, as a result of advances continually being made in the manufacture of chips, rapidly increasing amounts of computing power could be purchased for the same basic costs. Microprocessors equipped with ROM, or read-only memory (which stores constantly used, unchanging programs), now were also performing an increasing number of process-control, testing, monitoring, and diagnostic functions, as in automobile ignition-system, engine, and production line inspection tasks.
In the 1990s these changes were forcing the computer industry as a whole to make striking adjustments. Long-established and more recent giants of the field were reducing their work staffs, shutting down factories, and dropping subsidiaries. At the same time competition in the hardware field intensified and producers of personal computers continued to proliferate, as did specialty companies, each company devoting itself to some special area of manufacture, distribution, or customer service.
Computers continue to dwindle to increasingly convenient sizes for use in offices, schools, and homes. Programming productivity has not increased as rapidly, and as a result software has become the major cost of many systems. However, programming techniques such as object-oriented programming have been developed to help alleviate this problem. The computer field as a whole continues to experience tremendous growth. As computer and telecommunications technologies continue to integrate, computer networking, electronic mail, and electronic publishing are just a few of the applications that have matured in recent years. The most phenomenal growth has been in the development of the Internet, with attendant ramifications in software manufacture and other areas.
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