A Computer is a machine that manipulates data according to a set of instructions. Computers are able to do mathematical calculations. Modern computers can do complex mathematical computations -- billions per minute. Computers have been used to control industrial operations, which used to be routine clerical work. Recently, they have spread to the home, where they are used for media, web browsing and desktop applications.
History of computing.
It is difficult to identify any particular device as the earliest computer. This is because the meaning of the word "computer" has changed over time. Originally, the word referred to a person who did numerical calculations (a human computer). Human computers often used mechanical calculating devices to help them solve their problems.
The history of the modern computer begins with two separate technologies - that of automated calculation and that of programmability.
Examples of early mechanical calculating devices include the abacus, the slide rule and arguably the astrolabe and the Antikythera mechanism (which dates from about 150-100 BC). Hero of Alexandria (c. 10â€'70 AD) built a mechanical theater which performed a play lasting 10 minutes and was operated by a complex system of ropes and drums that might be considered to be a means of deciding which parts of the mechanism performed which actions and when. This is the essence of programmability.
The "castle clock", an astronomical clock invented by Al-Jazari in 1206, is considered to be the earliest programmable analog computer. It displayed the zodiac, the solar and lunar orbits, a crescent moon-shaped pointer travelling across a gateway causing automatic doors to open every hour, and five robotic musicians who play music when struck by levers operated by a camshaft attached to a water wheel. The length of day and night could be re-programmed every day in order to account for the changing lengths of day and night throughout the year.
At the end of the Middle Ages, European mathematics and engineering became more important. In 1623, Wilhelm Schickard constructed a device that is seen as the earliest of a number of mechanical calculators constructed by European engineers. None of these devices fit the modern definition of a computer, because they could not be programmed.
In 1801, Joseph Marie Jacquard made an improvement to the textile loom that used a series of punched paper cards as a template to allow his loom to weave intricate patterns automatically. The resulting Jacquard loom was an important step in the development of computers because the use of punched cards to define woven patterns can be viewed as an early, but limited, form of programmability.
Only when automatic calculation was combined with programmability did the first computers in the modern sense result. In 1837, Charles Babbage was the first to make a design of a fully programmable mechanical computer. He called it the "The Analytical Engine". Because Babbage did not have enough money and could not resist changing the design all the time, he never built his Analytical Engine.
Large-scale automated data processing of punched cards was performed for the U.S. Census in 1890 by tabulating machines designed by Herman Hollerith and manufactured by the Computing Tabulating Recording Corporation, which later became IBM. By the end of the 19th century a number of technologies that would later prove useful in the realization of practical computers had begun to appear: the punched card, Boolean algebra, the vacuum tube (thermionic valve) and the teleprinter.
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.
Several developers of ENIAC saw its problems. They invented a more flexible and elegant design, which is known as "stored program architecture" or von Neumann architecture. This design was first formally described by John von Neumann in the paper "First Draft of a Report on the EDVAC", distributed in 1945. A number of projects to develop computers based on the stored-program architecture started around this time, the first of these was completed in Great Britain. The first to be demonstrated working was the Manchester Small-Scale Experimental Machine (SSEM or "Baby"), while the EDSAC, completed a year after SSEM, was the first practical implementation of the stored program design. Shortly thereafter, the machine originally described by von Neumann's paperâ€'EDVACâ€'was completed but did not see full-time use for an additional two years.
Nearly all modern computers implement the stored-program architecture in some form. It has become the main concept which defines a modern computer. Most of the technologies used to build computers have changed since the 1940s, but many current computers still use the von-Neumann architecture.
Computers that used vacuum tubes as their electronic elements were in use throughout the 1950s. Vacuum tube electronics were largely replaced in the 1960s by transistor-based electronics, which are smaller, faster and cheaper to produce. They also need less power and are more reliable than vacuum tubes. In the 1970s, technologies were based on integrated circuits. Microprocessors, such as the Intel 4004, further decreased size and cost. They also made computers faster and more reliable. By the 1980s, computers became sufficiently small and cheap to replace simple mechanical controls in domestic appliances such as washing machines. The 1980s also saw home computers and the now ubiquitous personal computer. With the evolution of the Internet, personal computers are becoming as common as the television and the telephone in the household.
In 2005 Nokia started to call its top-line smartphones of the N-series "multimedia computers" and after the launch of the Apple iPhone in 2007, many are now starting to add the smartphone category among "real" computers. In 2008, if the category of smartphones are included in the numbers of computers in the world, the biggest computer maker by units sold, is no longer Hewlett-Packard, but rather Nokia.
Kinds of computers.
A "desktop computer" is a small machine which is usually accompanied by a screen (which isn't part of the computer) and used at a household. "Laptop computers" are portable computers that are commonly used for work or personal media purposes. Both laptops and desktops are considered personal computers. "Mainframes" are large computers used for managing businesses or hosting servers. "Embedded computers" are computer systems that cannot be programmed by the user because they are preprogrammed for a specific task and are buried within the equipment they serve. For example, in mobile phones, Automatic Teller Machines, Microwave ovens, CD Players and Cars.
How computers work.
Computers store data and the instructions telling them what to do with the data as numbers, because computers can do things with numbers very quickly. These data are stored as binary symbols (1s and 0s). A 1 or a 0 symbol stored by a computer is called a bit, which comes from the words binary digit. Computers can use many bits together to represent instructions and the data that these instructions use. A list of these instructions is called a program and stored on the computer's hard disk. Computers use "memory" called "RAM" as a space to carry out the instructions and store data while it is doing these instructions. When the computer wants to store the results of the instructions for later, it uses the hard disk.
An operating system tells the computer how to understand what jobs it has to do, how to do these jobs, and how to tell people the results. It tells the electronics inside the computer, or "hardware", how to work to get the results it needs. This lets most computers have the same operating system, or list of orders to tell it how to talk to the user, while each computer can have its own computer programs or list of jobs to do what its user needs. Having different programs and operating systems makes it easy to learn how to use computers for new things. When a user needs to use a computer for something different, the user can learn how to use a new program.
Computers and the Internet.
One of the most important jobs that computers do for people is helping with communication. Communication is how people share information. Computers have helped people move forward in science, medicine, business, and learning, because they let experts from anywhere in the world work with each other and share information. They also let other people communicate with each other, do their jobs almost anywhere, learn about almost anything, or share their opinions with each other. The Internet is the thing that lets people communicate between their computers.
Blogs are used by many people to say what they want on the Internet. Some people spend most of their time reading and writing blogs. Many people from all over the world use them. Some people use them to write about things that happen to them. Experts can use them to help people learn more. Some blogs are used by companies to sell things.
Computers and waste.
A computer is now almost always an electronic device. It usually contains materials that will become toxic waste when disposed of. When a new computer is bought in some places, laws require that the cost of its waste management must also be paid for. This is called product stewardship.
Computers can become obsolete quickly, depending on what programs the user runs. Very often, they are thrown away within two or three years, because newer programs require a more powerful computer. This makes the problem worse, so computer recycling happens a lot. Many projects try to send working computers to developing nations so they can be re-used and will not become waste as quickly, as most people do not need to run new programs.
The main hardware in a computer.
Computers come different forms, but most of them have a common architecture.
A computer has several main parts. When comparing a computer to a human body, the CPU is like a brain. It does most of the 'thinking' and tells the rest of the computer how to work. The CPU is on the Motherboard, which is like the skeleton. It provides the basis for where the other parts go, and carries the nerves that connect them to each other and the CPU. The motherboard is connected to a power supply, which provides electricity to the entire computer. The various drives (CD drive, floppy drive, and on many newer computers, USB drive) act like
eyes, ears, and fingers, and allow the computer to read different types of storage, in the same way that a human can read different types of books. The hard drive is like a human's memory, and keeps track of all the data stored on the computer. Most computers have a sound card or another method of making sound, which is like vocal cords, or a voice box. Connected to the sound card are speakers, which are like a mouth, and are where the sound comes out. Computers might also have a graphics card, which helps the computer to create visual effects, such as 3D environments, or more realistic colors, and more powerful graphics cards can make more realistic or more advanced images, in the same way a well trained artist can.

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