Before the development of the general-purpose computer, most calculations were done by humans. Tools to help humans calculate were then called "calculating machines", by proprietary names, or even as they are now, calculators. It was those humans who used the machines who were then called computers; there are pictures of enormous rooms filled with desks at which computers (often young women) used their machines to jointly perform calculations, as for instance, aerodynamic ones required for in aircraft design.
Calculators have continued to develop, but computers add the critical element of conditional response and larger memory, allowing automation of both numerical calculation and in general, automation of many symbol-manipulation tasks. Computer technology has undergone profound changes every decade since the 1940s.
Computing hardware has become a platform for uses other than mere computation, such as process automation, electronic communications, equipment control, entertainment, education, etc. Each field in turn has imposed its own requirements on the hardware, which has evolved in response to those requirements, such as the role of the touch screen to create a more intuitive and natural user interface.
Aside from written numerals, the first aids to computation were purely mechanical devices which required the operator to set up the initial values of an elementary arithmetic operation, then manipulate the device through manual manipulations to obtain the result. A sophisticated (and comparatively recent) example is the slide rule in which numbers are represented as lengths on a logarithmic scale and computation is performed by setting a cursor and aligning sliding scales, thus adding those lengths. Numbers could be represented in a continuous "analog" form, for instance a voltage or some other physical property was set to be proportional to the number. Analog computers, like those designed and built by Vannevar Bush before World War II were of this type. Or, numbers could be represented in the form of digits, automatically manipulated by a mechanical mechanism. Although this last approach required more complex mechanisms in many cases, it made for greater precision of results.
Both analog and digital mechanical techniques continued to be developed, producing many practical computing machines. Electrical methods rapidly improved the speed and precision of calculating machines, at first by providing motive power for mechanical calculating devices, and later directly as the medium for representation of numbers. Numbers could be represented by voltages or currents and manipulated by linear electronic amplifiers. Or, numbers could be represented as discrete binary or decimal digits, and electrically controlled switches and combinational circuits could perform mathematical operations.
The invention of electronic amplifiers made calculating machines much faster than their mechanical or electromechanical predecessors. Vacuum tube (thermionic valve) amplifiers gave way to solid state transistors, and then rapidly to integrated circuits which continue to improve, placing millions of electrical switches (typically transistors) on a single elaborately manufactured piece of semi-conductor the size of a fingernail. By defeating the tyranny of numbers, integrated circuits made high-speed and low-cost digital computers a widespread commodity. Scottish mathematician and physicist John Napier noted multiplication and division of numbers could be performed by addition and subtraction, respectively, of logarithms of those numbers. While producing the first logarithmic tables Napier needed to perform many multiplications, and it was at this point that he designed Napier's bones, an abacus-like device used for multiplication and division. Since real numbers can be represented as distances or intervals on a line, the slide rule was invented in the 1620s to allow multiplication and division operations to be carried out significantly faster than was previously possible.Slide rules were used by generations of engineers and other mathematically involved professional workers, until the invention of the pocket calculator.
Yazu Arithmometer. Patented in Japan in 1903. Note the lever for turning the gears of the calculator.
Wilhelm Schickard, a German polymath, designed a calculating clock in 1623, unfortunately a fire destroyed it during its construction in 1624 and Schickard abandoned the project. Two sketches of it were discovered in 1957; too late to have any impact on the development of mechanical calculators.
In 1642, while still a teenager, Blaise Pascal started some pioneering work on calculating machines and after three years of effort and 50 prototypes he invented the mechanical calculator.He built twenty of these machines (called the Pascaline) in the following ten years.
Gottfried Wilhelm von Leibniz invented the Stepped Reckoner and his famous cylinders around 1672 while adding direct multiplication and division to the Pascaline. Leibniz once said "It is unworthy of excellent men to lose hours like slaves in the labour of calculation which could safely be relegated to anyone else if machines were used."
Around 1820, Charles Xavier Thomas created the first successful, mass-produced mechanical calculator, the Thomas Arithmometer, that could add, subtract, multiply, and divide. It was mainly based on Leibniz' work. Mechanical calculators, like the base-ten addiator, the comptometer, the Monroe, the Curta and the Addo-X remained in use until the 1970s. Leibniz also described the binary numeral system,a central ingredient of all modern computers. However, up to the 1940s, many subsequent designs (including Charles Babbage's machines of the 1822 and even ENIAC of 1945) were based on the decimal system; ENIAC's ring counters emulated the operation of the digit wheels of a mechanical adding machine.
In Japan, Ryōichi Yazu patented a mechanical calculator called the Yazu Arithmometer in 1903. It consisted of a single cylinder and 22 gears, and employed the mixed base-2 and base-5 number system familiar to users to the soroban (Japanese abacus). Carry and end of calculation were determined automatically. More than 200 units were sold, mainly to government agencies such as the Ministry of War and agricultural experiment stations
In 1801, Joseph-Marie Jacquard developed a loom in which the pattern being woven was controlled by punched cards. The series of cards could be changed without changing the mechanical design of the loom. This was a landmark achievement in programmability. His machine was an improvement over similar weaving looms. Punch cards were preceded by punch bands like as in the machine proposed by Basile Bouchon. These bands would inspire information recording for automatic pianos and more recently NC machine-tools.
In 1833, Charles Babbage moved on from developing his difference engine (for navigational calculations) to a general purpose design, the Analytical Engine, which drew directly on Jacquard's punched cards for its program storage. In 1835, Babbage described his analytical engine. It was a general-purpose programmable computer, employing punch cards for input and a steam engine for power, using the positions of gears and shafts to represent numbers. His initial idea was to use punch-cards to control a machine that could calculate and print logarithmic tables with huge precision (a special purpose machine). Babbage's idea soon developed into a general-purpose programmable computer. While his design was sound and the plans were probably correct, or at least debuggable, the project was slowed by various problems including disputes with the chief machinist building parts for it. Babbage was a difficult man to work with and argued with everyone. All the parts for his machine had to be made by hand. Small errors in each item might sometimes sum to cause large discrepancies. In a machine with thousands of parts, which required these parts to be much better than the usual tolerances needed at the time, this was a major problem. The project dissolved in disputes with the artisan who built parts and ended with the decision of the British Government to cease funding. Ada Lovelace, Lord Byron's daughter, translated and added notes to the "Sketch of the Analytical Engine" by Federico Luigi, Conte Menabrea. This appears to be the first published description of programming.
A reconstruction of the Difference Engine II, an earlier, more limited design, has been operational since 1991 at the London Science Museum. With a few trivial changes, it works exactly as Babbage designed it and shows that Babbage's design ideas were correct, merely too far ahead of his time. The museum used computer-controlled machine tools to construct the necessary parts, using tolerances a good machinist of the period would have been able to achieve. Babbage's failure to complete the analytical engine can be chiefly attributed to difficulties not only of politics and financing, but also to his desire to develop an increasingly sophisticated computer and to move ahead faster than anyone else could follow.
Following Babbage, although unaware of his earlier work, was Percy Ludgate, an accountant from Dublin, Ireland. He independently designed a programmable mechanical computer, which he described in a work that was published in 1909.
In the late 1880s, the American Herman Hollerith invented data storage on a medium that could then be read by a machine. Prior uses of machine readable media had been for control (automatons such as piano rolls or looms), not data. "After some initial trials with paper tape, he settled on punched cards..." Hollerith came to use punched cards after observing how railroad conductors encoded personal characteristics of each passenger with punches on their tickets. To process these punched cards he invented the tabulator, and the key punch machine. These three inventions were the foundation of the modern information processing industry. His machines used mechanical relays (and solenoids) to increment mechanical counters. Hollerith's method was used in the 1890 United States Census and the completed results were "... finished months ahead of schedule and far under budget". Indeed years faster than the prior census had required. Hollerith's company eventually became the core of IBM. IBM developed punch card technology into a powerful tool for business data-processing and produced an extensive line of unit record equipment. By 1950, the IBM card had become ubiquitous in industry and government. The warning printed on most cards intended for circulation as documents (checks, for example), "Do not fold, spindle or mutilate," became a catch phrase for the post-World War II era.
Leslie Comrie's articles on punched card methods and W.J. Eckert's publication of Punched Card Methods in Scientific Computation in 1940, described punch card techniques sufficiently advanced to solve some differential equations or perform multiplication and division using floating point representations, all on punched cards and unit record machines. Those same machines had been used during World War II for cryptographic statistical processing. In the image of the tabulator (see left), note the patch panel, which is visible on the right side of the tabulator. A row of toggle switches is above the patch panel. The Thomas J. Watson Astronomical Computing Bureau, Columbia University performed astronomical calculations representing the state of the art in computing. Computer programming in the punch card era was centered in the "computer center". Computer users, for example science and engineering students at universities, would submit their programming assignments to their local computer center in the form of a stack of punched cards, one card per program line. They then had to wait for the program to be read in, queued for processing, compiled, and executed. In due course, a printout of any results, marked with the submitter's identification, would be placed in an output tray, typically in the computer center lobby. In many cases these results would be only a series of error messages, requiring yet another edit-punch-compile-run cycle. Punched cards are still used and manufactured to this day, and their distinctive dimensions (and 80-column capacity) can still be recognized in forms, records, and programs around the world. They are the size of American paper currency in Hollerith's time, a choice he made because there was already equipment available to handle bills.
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