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قديم December 14, 2008, 12:19 AM
 
Computer The Computer

A Computer : is a machine that manipulates data according to a list of instructions.
The first devices that resemble modern computers date to the mid-20th century (1940–1945), although the computer concept and various machines similar to computers existed earlier. Early electronic computers were the size of a large room, consuming as much power as several hundred modern personal computers(PC).[1] Modern computers are based on tiny integrated circuits and are millions to billions of times more capable while occupying a fraction of the space.[2] Today, simple computers may be made small enough to fit into a wristwatch and be powered from a watch battery. Personal computers, in various forms, are icons of the Information Age and are what most people think of as "a computer"; however, the most common form of computer in use today is the embedded computer. Embedded computers are small, simple devices that are used to control other devices — for example, they may be found in machines ranging from fighter aircraft to industrial robots, digital cameras, and children's toys.
The ability to store and execute lists of instructions called programs makes computers extremely versatile and distinguishes them from calculators. The Church–Turing thesis is a mathematical statement of this versatility: any computer with a certain minimum capability is, in principle, capable of performing the same tasks that any other computer can perform. Therefore, computers with capability and complexity ranging from that of a personal digital assistant to a supercomputer are all able to perform the same computational tasks given enough time and storage capacity.
History Of Computing
Main article: History of computer hardware




























The Jacquard loom was one of the first programmable devices.
It is difficult to identify any one device as the earliest computer, partly because the term "computer" has been subject to varying interpretations over time. Originally, the term "computer" referred to a person who performed numerical calculations (a human computer), often with the aid of a mechanical calculating device.
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 included the abacus, the slide rule and arguably the astrolabe and the Antikythera mechanism (which dates from about 150-100 BC). Hero of Alexandria (c. 10–70 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.[3] 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.[4] 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,[5][6] 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.[4]
The end of the Middle Ages saw a re-invigoration of European mathematics and engineering, and Wilhelm Schickard's 1623 device was the first of a number of mechanical calculators constructed by European engineers. However, none of those devices fit the modern definition of a computer because they could not be programmed.
In 1801, Joseph Marie Jacquard made an improvement to the ****ile 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, albeit limited, form of programmability.
It was the fusion of automatic calculation with programmability that produced the first recognizable computers. In 1837, Charles Babbage was the first to conceptualize and design a fully programmable mechanical computer that he called "The Analytical Engine".[7] Due to limited finances, and an inability to resist tinkering with the design, Babbage never actually 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.
Defining characteristics of some early digital computers of the 1940s (In the history of computing hardware)

Name First operational Numeral system Computing mechanism Programming
Turing complete

Zuse Z3 (Germany) May 1941 Binary
Electro-mechanical
Program-controlled by punched film stock
Yes (1998)

Atanasoff–Berry Computer (US)
mid-1941 Binary
Electronic
Not programmable—single purpose No
Colossus (UK)
January 1944 Binary
Electronic
Program-controlled by patch cables and switches No
Harvard Mark I – IBM ASCC (US) 1944 Decimal
Electro-mechanical
Program-controlled by 24-channel punched paper tape (but no conditional branch) No
ENIAC (US)
November 1945 Decimal
Electronic
Program-controlled by patch cables and switches Yes
Manchester Small-Scale Experimental Machine (UK)
June 1948 Binary
Electronic
Stored-program in Williams cathode ray tube memory
Yes
Modified ENIAC (US)
September 1948 Decimal
Electronic
Program-controlled by patch cables and switches plus a primitive read-only stored programming mechanism using the Function Tables as program ROM
Yes
EDSAC (UK)
May 1949 Binary
Electronic
Stored-program in mercury delay line memory
Yes
Manchester Mark I (UK)
October 1949 Binary
Electronic
Stored-program in Williams cathode ray tube memory and magnetic drum memory
Yes
CSIRAC (Australia) November 1949 Binary
Electronic
Stored-program in mercury delay line memory
Yes
A succession of steadily more powerful and flexible computing devices were constructed in the 1930s and 1940s, gradually adding the key features that are seen in modern computers. The use of digital electronics (largely invented by Claude Shannon in 1937) and more flexible programmability were vitally important steps, but defining one point along this road as "the first digital electronic computer" is difficult (Shannon 1940). Notable achievements include:





EDSAC was one of the first computers to implement the stored program (von Neumann) architecture.
• Konrad Zuse's electromechanical "Z machines". The Z3 (1941) was the first working machine featuring binary arithmetic, including floating point arithmetic and a measure of programmability. In 1998 the Z3 was proved to be Turing complete, therefore being the world's first operational computer.
• The non-programmable Atanasoff–Berry Computer (1941) which used vacuum tube based computation, binary numbers, and regenerative capacitor memory.
• The secret British Colossus computers (1943)[8], which had limited programmability but demonstrated that a device using thousands of tubes could be reasonably reliable and electronically reprogrammable. It was used for breaking German wartime codes.
• The Harvard Mark I (1944), a large-scale electromechanical computer with limited programmability.
• The U.S. Army's Ballistics Research Laboratory ENIAC (1946), which used decimal arithmetic and is sometimes called the first general purpose electronic computer (since Konrad Zuse's Z3 of 1941 used electromagnets instead of electronics). Initially, however, ENIAC had an inflexible architecture which essentially required rewiring to change its programming.
Several developers of ENIAC, recognizing its flaws, came up with a far more flexible and elegant design, which came to be known as the "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 commenced around this time, the first of these being 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 paper—EDVAC—was completed but did not see full-time use for an additional two years.
Nearly all modern computers implement some form of the stored-program architecture, making it the single trait by which the word "computer" is now defined. While the technologies used in computers have changed dramatically since the first electronic, general-purpose computers of the 1940s, most still use the von Neumann architecture.


Microprocessors are miniaturized devices that often implement stored program CPUs.
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, cheaper to produce, require less power, and are more reliable. In the 1970s, integrated circuit technology and the subsequent creation of microprocessors, such as the Intel 4004, further decreased size and cost and further increased speed and reliability of computers. By the 1980s, computers became sufficiently small and cheap to replace simple mechanical controls in domestic appliances such as washing machines. The 1980s also witnessed 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.
How computers work
Main articles: Central processing unit and Microprocessor
A general purpose computer has four main sections: the arithmetic and logic unit (ALU), the control unit, the memory, and the input and output devices (collectively termed I/O). These parts are interconnected by busses, often made of groups of wires.
The control unit, ALU, registers, and basic I/O (and often other hardware closely linked with these) are collectively known as a central processing unit (CPU). Early CPUs were composed of many separate components but since the mid-1970s CPUs have typically been constructed on a single integrated circuit called a microprocessor.
Why computer is important in the modren world?
In: Computers
[Edit]


Anthony lee perception ......
Computer is important in the modern world reason been is that it helpes to simpifies life. If it was't for computer there would still be a lot of hidden information, people woul not get to communicate so easy, fast and efficiently, hopwever it is not like that because of computer we now get previllage of al these things.
The Many Uses of Computer
Computers are helpful because they offer a wide range of s functions and services that are not available anywhere else. There are four main uses: word processing, internet/communications, digital video/audio composition, and desktop publishing. Although one can create a typed paper with a typewriter, the computer has more features
to do it with. Internet and communications, digital video and audio composition, and desktop publishing are all features that are only offered on computers. With these tools human society has progressed exponentially.

The word processing capabilities of computers are amazing. They can automatically correct your spelling and grammar mistakes. The cutting and pasting features are incredibly simple and very useful for revision. Plus it is easier to read a word-processed ******** than one written by hand. Having a digital backup is an added benefit. All of these things help writers get the job done. If you want to add pictures to your writing, numerous software titles are available for desktop publishing. With desktop publishing, you can create page layouts for entire books on your home computer. For example, high school yearbook classes now use desktop publishing software for the creation and design
of their yearbooks. Most of this cannot be done by hand, and if so, then it is painstakingly laborious.

The Internet is one of the greatest inventions of humanity. It is a massive network of computers, each with the ability to access any of the others. Ungodly amounts of information can be found on the Internet. It is the ultimate form of media, a combination of newspaper, radio, and as the average bandwidth is increasing, television. Using
the Internet, any two people anywhere can communicate for free, whether it is with **** or voice. Video conferencing tools are becoming readily available to the public. New uses are being found for the Internet every day.

Audio/video editing and composition have been made much easier by computers. Cutting and pasting is no longer comprised of using scissors and tape on large reels of film. It no longer costs thousands of dollars of equipment to make a film or to compose music. Now emerging musicians have the ability to compose their own songs and publish them without having to obtain a record contract. Amateur filmmakers can produce work from their own homes. Graphics engineers can use computers to create three-dimensional models, or even to generate short or full-length films. Anybody who owns a computer can now enter the field of media production.

Computers have so many uses that cannot be found anywhere else. Word processors are the perfect writing device because you can compose quickly and make changes easily. The Internet provides a fast, free, and unique way to get information or to communicate with others. Computers supply an affordable solution to nonprofessional audio and video composition. These reasons are why computers are so helpful in modern society. With the aid of computers, humankind is entering a new era of enlightenmeComputers - Possible Negative Effects Of Computer Use, Possible Positive Effects Of Computer Use, Developmentally Appropriate Uses Of Computers
Computers are ubiquitous. As computers have become less expensive they have been purchased by more and more families for their homes. Because of this, many children begin to use computers at an early age. Even if computers are not available in their home, children almost certainly will begin to come into contact with computers in school.
Some adults are amazed by how readily young children use computers. Many children find that using computers gives them a sense of power and accomplishment. And, unlike many adults whose first or primary contact with computers is work related, most children first use computers for entertainment purposes and games. This is by no means the only use that children have for computers. Children also use computers for accessing information, as well as for writing stories and research papers.
In addition, children use a variety of learning programs, which either seek to teach or reinforce basic skills in math, language, reading, and other subjects. Other software allows children to draw pictures or create visual works of art and self-expression. Communication with others is growing as an application of computers by children, particularly as more homes and schools gain access to the Internet. As computers continue to become more powerful, increasing numbers of children are using computers to create multimedia presentations and even web sites that include pictures, ****, audio, and even video.
Because computer use is promoted in schools, and because computers are so ubiquitous, children have a great deal of exposure to them. Not everyone, however, is comfortable with the use of computers by young children. Some, including the Alliance for Childhood, have called for a halt to the use of computers by young children. Such groups cite the costs as well as possible health effects that using computers may have on children. The true impact that early computer use has on children is uncertain. Even though there is not enough information to state authoritatively that computers have any negative effects on children, the possible adverse effects that have been cited are serious enough to warrant consideration.
Conclusion
Children can use computers in effective and positive ways. Positive uses of computers by children are developmentally appropriate and can reinforce the attainment of desirable skills and traits such as math mastery, verbal language use, and cooperation skills. Computers, however, can also be used in ways that may be harmful to the child. Possible harmful effects from computers, such as repetitive motion injuries and eyestrain, most often stem from

overuse of computers and use of computers that are positioned inappropriately for children. If children are to use computers, they should be taught to limit their computer use to reasonable might expose them to inappropriate
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