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A computer is a digital electronic machine that can be programmed to carry out sequences of arithmetic or logical operations computation automatically. Modern computers can perform generic sets of operations known as programs. These programs enable computers to perform a wide range of tasks. A computer system is a "complete" computer that includes the hardware , operating system main software , and peripheral equipment needed and used for "full" operation. This term may also refer to a group of computers that are linked and function together, such as a computer network or computer cluster.
A broad range of industrial and consumer products use computers as control systems. Simple special-purpose devices like microwave ovens and remote controls are included, as are factory devices like industrial robots and computer-aided design , as well as general-purpose devices like personal computers and mobile devices like smartphones. Computers power the Internet , which links billions of other computers and users. Early computers were meant to be used only for calculations.
Simple manual instruments like the abacus have aided people in doing calculations since ancient times. Early in the Industrial Revolution , some mechanical devices were built to automate long tedious tasks, such as guiding patterns for looms. More sophisticated electrical machines did specialized analog calculations in the early 20th century.
The first digital electronic calculating machines were developed during World War II. The first semiconductor transistors in the late s were followed by the silicon -based MOSFET MOS transistor and monolithic integrated circuit IC chip technologies in the late s, leading to the microprocessor and the microcomputer revolution in the s.
The speed, power and versatility of computers have been increasing dramatically ever since then, with transistor counts increasing at a rapid pace as predicted by Moore's law , leading to the Digital Revolution during the late 20th to early 21st centuries. Conventionally, a modern computer consists of at least one processing element , typically a central processing unit CPU in the form of a microprocessor , along with some type of computer memory , typically semiconductor memory chips.
The processing element carries out arithmetic and logical operations, and a sequencing and control unit can change the order of operations in response to stored information.
Peripheral devices include input devices keyboards, mice, joystick , etc. Peripheral devices allow information to be retrieved from an external source and they enable the result of operations to be saved and retrieved. According to the Oxford English Dictionary , the first known use of computer was in a book called The Yong Mans Gleanings by the English writer Richard Brathwait : "I haue [ sic ] read the truest computer of Times, and the best Arithmetician that euer [sic] breathed, and he reduceth thy dayes into a short number.
The word continued with the same meaning until the middle of the 20th century. During the latter part of this period women were often hired as computers because they could be paid less than their male counterparts. The Online Etymology Dictionary gives the first attested use of computer in the s, meaning 'one who calculates'; this is an "agent noun from compute v.
The Online Etymology Dictionary states that the use of the term to mean " 'calculating machine' of any type is from Devices have been used to aid computation for thousands of years, mostly using one-to-one correspondence with fingers.
The earliest counting device was probably a form of tally stick. Later record keeping aids throughout the Fertile Crescent included calculi clay spheres, cones, etc. The abacus was initially used for arithmetic tasks. The Roman abacus was developed from devices used in Babylonia as early as BC. Since then, many other forms of reckoning boards or tables have been invented. In a medieval European counting house , a checkered cloth would be placed on a table, and markers moved around on it according to certain rules, as an aid to calculating sums of money.
The Antikythera mechanism is believed to be the earliest known mechanical analog computer , according to Derek J. It was discovered in in the Antikythera wreck off the Greek island of Antikythera , between Kythera and Crete , and has been dated to approximately c.
Devices of comparable complexity to the Antikythera mechanism would not reappear until the fourteenth century. Many mechanical aids to calculation and measurement were constructed for astronomical and navigation use. A combination of the planisphere and dioptra , the astrolabe was effectively an analog computer capable of working out several different kinds of problems in spherical astronomy. An astrolabe incorporating a mechanical calendar computer [9] [10] and gear -wheels was invented by Abi Bakr of Isfahan , Persia in The sector , a calculating instrument used for solving problems in proportion, trigonometry, multiplication and division, and for various functions, such as squares and cube roots, was developed in the late 16th century and found application in gunnery, surveying and navigation.
The planimeter was a manual instrument to calculate the area of a closed figure by tracing over it with a mechanical linkage. The slide rule was invented around — by the English clergyman William Oughtred , shortly after the publication of the concept of the logarithm. It is a hand-operated analog computer for doing multiplication and division.
As slide rule development progressed, added scales provided reciprocals, squares and square roots, cubes and cube roots, as well as transcendental functions such as logarithms and exponentials, circular and hyperbolic trigonometry and other functions.
Slide rules with special scales are still used for quick performance of routine calculations, such as the E6B circular slide rule used for time and distance calculations on light aircraft. In the s, Pierre Jaquet-Droz , a Swiss watchmaker , built a mechanical doll automaton that could write holding a quill pen. By switching the number and order of its internal wheels different letters, and hence different messages, could be produced.
In effect, it could be mechanically "programmed" to read instructions. In —, mathematician and engineer Giovanni Plana devised a Perpetual Calendar machine , which, through a system of pulleys and cylinders and over, could predict the perpetual calendar for every year from AD 0 that is, 1 BC to AD , keeping track of leap years and varying day length. The tide-predicting machine invented by the Scottish scientist Sir William Thomson in was of great utility to navigation in shallow waters. It used a system of pulleys and wires to automatically calculate predicted tide levels for a set period at a particular location.
The differential analyser , a mechanical analog computer designed to solve differential equations by integration , used wheel-and-disc mechanisms to perform the integration. In , Sir William Thomson had already discussed the possible construction of such calculators, but he had been stymied by the limited output torque of the ball-and-disk integrators. The torque amplifier was the advance that allowed these machines to work. Starting in the s, Vannevar Bush and others developed mechanical differential analyzers.
Charles Babbage , an English mechanical engineer and polymath , originated the concept of a programmable computer. Considered the " father of the computer ", [17] he conceptualized and invented the first mechanical computer in the early 19th century.
After working on his revolutionary difference engine , designed to aid in navigational calculations, in he realized that a much more general design, an Analytical Engine , was possible. The input of programs and data was to be provided to the machine via punched cards , a method being used at the time to direct mechanical looms such as the Jacquard loom. For output, the machine would have a printer, a curve plotter and a bell.
The machine would also be able to punch numbers onto cards to be read in later. The Engine incorporated an arithmetic logic unit , control flow in the form of conditional branching and loops , and integrated memory , making it the first design for a general-purpose computer that could be described in modern terms as Turing-complete.
The machine was about a century ahead of its time. All the parts for his machine had to be made by hand — this was a major problem for a device with thousands of parts. Eventually, the project was dissolved with the decision of the British Government to cease funding. Babbage's failure to complete the analytical engine can be chiefly attributed to political and financial difficulties as well as his desire to develop an increasingly sophisticated computer and to move ahead faster than anyone else could follow.
Nevertheless, his son, Henry Babbage , completed a simplified version of the analytical engine's computing unit the mill in He gave a successful demonstration of its use in computing tables in During the first half of the 20th century, many scientific computing needs were met by increasingly sophisticated analog computers , which used a direct mechanical or electrical model of the problem as a basis for computation.
However, these were not programmable and generally lacked the versatility and accuracy of modern digital computers. The differential analyser , a mechanical analog computer designed to solve differential equations by integration using wheel-and-disc mechanisms, was conceptualized in by James Thomson , the elder brother of the more famous Sir William Thomson.
The art of mechanical analog computing reached its zenith with the differential analyzer , built by H. This built on the mechanical integrators of James Thomson and the torque amplifiers invented by H. A dozen of these devices were built before their obsolescence became obvious. By the s, the success of digital electronic computers had spelled the end for most analog computing machines, but analog computers remained in use during the s in some specialized applications such as education slide rule and aircraft control systems.
By , the United States Navy had developed an electromechanical analog computer small enough to use aboard a submarine. This was the Torpedo Data Computer , which used trigonometry to solve the problem of firing a torpedo at a moving target. During World War II similar devices were developed in other countries as well.
Early digital computers were electromechanical ; electric switches drove mechanical relays to perform the calculation. These devices had a low operating speed and were eventually superseded by much faster all-electric computers, originally using vacuum tubes. The Z2 , created by German engineer Konrad Zuse in , was one of the earliest examples of an electromechanical relay computer.
In , Zuse followed his earlier machine up with the Z3 , the world's first working electromechanical programmable , fully automatic digital computer. It was quite similar to modern machines in some respects, pioneering numerous advances such as floating-point numbers. Rather than the harder-to-implement decimal system used in Charles Babbage 's earlier design , using a binary system meant that Zuse's machines were easier to build and potentially more reliable, given the technologies available at that time.
Zuse's next computer, the Z4 , became the world's first commercial computer; after initial delay due to the Second World War, it was completed in and delivered to the ETH Zurich.
Purely electronic circuit elements soon replaced their mechanical and electromechanical equivalents, at the same time that digital calculation replaced analog. The engineer Tommy Flowers , working at the Post Office Research Station in London in the s, began to explore the possible use of electronics for the telephone exchange.
Experimental equipment that he built in went into operation five years later, converting a portion of the telephone exchange network into an electronic data processing system, using thousands of vacuum tubes. The German encryption machine, Enigma , was first attacked with the help of the electro-mechanical bombes which were often run by women.
Colossus was the world's first electronic digital programmable computer. It had paper-tape input and was capable of being configured to perform a variety of boolean logical operations on its data, but it was not Turing-complete.
Colossus Mark I contained 1, thermionic valves tubes , but Mark II with 2, valves, was both five times faster and simpler to operate than Mark I, greatly speeding the decoding process. Like the Colossus, a "program" on the ENIAC was defined by the states of its patch cables and switches, a far cry from the stored program electronic machines that came later.
Once a program was written, it had to be mechanically set into the machine with manual resetting of plugs and switches. It combined the high speed of electronics with the ability to be programmed for many complex problems.
It could add or subtract times a second, a thousand times faster than any other machine. It also had modules to multiply, divide, and square root.
High speed memory was limited to 20 words about 80 bytes. Built under the direction of John Mauchly and J. The machine was huge, weighing 30 tons, using kilowatts of electric power and contained over 18, vacuum tubes, 1, relays, and hundreds of thousands of resistors, capacitors, and inductors.
The principle of the modern computer was proposed by Alan Turing in his seminal paper, [42] On Computable Numbers.
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