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The modern electronic digital computer is the result of a long series of developments, which started some 5000 years ago with the abacus. The first mechanical adding device was developed in 1642 by the French scientist-philosopher, Pascal. His ‘arithmetic machine’, was followed by the ‘stepped reckoner’ invented by Leibnitz in 1671, which was capable of also doing multiplication, division, and the evaluation of square roots by a series of stepped additions, not unlike the methods used in modern digital computers. In 1835, Charles Babbage formulated his concept of an ‘analytical machine’ which combined arithmetic processes with decisions based on the results of the computations. This was really the forerunner of the modern digital computer, in that it combined the principles of sequential control, branching, looping, and storage units.

In the later 19th-c, George Boole developed the symbolic binary logic which led to Boolean algebra and the binary switching methodology used in modern computers. Herman Hollerith (1860–1929), a US statistician, developed punched card techniques, mainly to aid with the US census at the beginning of the 20th-c; this advanced the concept of automatic processing, but major developments awaited the availability of suitable electronic devices. J Presper Eckert (1919–95) and John W Mauchly (1907–80) produced the first all-electronic digital computer, ENIAC (Electronic Numerical Integrator and Calculator), at the University of Pennsylvania in 1946, which was 1000 times faster than the mechanical computers. Their development of ENIAC led to one of the first commercial computers, UNIVAC I, in the early 1950s, which was able to handle both numerical and alphabetical information. Very significant contributions were made around this time by Johann von Neumann, who converted the ENIAC principles to give the EDVAC computer (Electronic Discrete Variable Automatic Computer) which could modify its own programs in much the same way as suggested by Babbage.

The first stored program digital computer to run an actual program was built at Manchester University, UK, and first performed successfully in 1948. This computer was later developed into the Ferranti Mark I computer, widely sold. The first digital computer (EDSAC) to be able to be offered as a service to users was developed at Cambridge University, UK, and ran in the spring of 1949. The EDSAC design was used as the basis of the first business computer system, the Lyons Electronic Office. Advances followed rapidly from the 1950s, and were further accelerated from the mid-1960s by the successful development of miniaturization techniques in the electronics industry. The first microprocessor, which might be regarded as a computer on a chip, appeared in 1971, and nowadays the power of even the most modest personal computer can equal or outstrip the early electronic computers of the 1940s. The key elements in computing today are miniaturization and communications. Hand-held computers, with input via a stylus, can be linked to central systems through a mobile telephone.

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A computer is a machine for manipulating data according to a list of instructions known as a program.

Computers are extremely versatile. According to the Church?Turing thesis, a computer with a certain minimum threshold capability is in principle capable of performing the tasks of any other computer. Therefore, computers with capabilities ranging from those of a personal digital assistant to a supercomputer may all perform the same tasks, as long as time and memory capacity are not considerations. Therefore, the same computer designs may be adapted for tasks ranging from processing company payrolls to controlling unmanned spaceflights. Due to technological advancement, modern electronic computers are exponentially more capable than those of preceding generations (a phenomenon partially described by Moore's Law).

Computers take numerous physical forms. Early electronic computers were the size of a large room, while entire modern embedded computers may be smaller than a deck of playing cards. Even today, enormous computing facilities still exist for specialized scientific computation and for the transaction processing requirements of large organizations. Smaller computers designed for individual use are called personal computers. Along with its portable equivalent, the laptop computer, the personal computer is the ubiquitous information processing and communication tool, and is usually what is meant by "a computer". However, the most common form of computer in use today is the embedded computer. They may control machines from fighter aircraft to industrial robots to digital cameras.

History of computing

Originally, the term "computer" referred to a person who performed numerical calculations, often with the aid of a mechanical calculating device or analog computer. Examples of these early devices, the ancestors of the computer, included the abacus and the Antikythera mechanism, an ancient Greek device for calculating the movements of planets which dates from about 87 BC. The end of the Middle Ages saw a reinvigoration of European mathematics and engineering, and Wilhelm Schickard's 1623 device was the first of a number of mechanical calculators constructed by European engineers.

In 1801, Joseph Marie Jacquard made an improvement to existing loom designs that used a series of punched paper cards as a program to weave intricate patterns. The resulting Jacquard loom is not considered a true computer but it was an important step in the development of modern digital computers.

Charles Babbage was the first to conceptualize and design a fully programmable computer as early as 1820, but due to a combination of the limits of the technology of the time, limited finance, and an inability to resist tinkering with his design, the device was never actually constructed in his lifetime. By the end of the 19th century a number of technologies that would later prove useful in computing had appeared, such as the punch card and the vacuum tube, and large-scale automated data processing using punch cards was performed by tabulating machines designed by Hermann Hollerith.

During the first half of the 20th century, many scientific computing needs were met by increasingly sophisticated special-purpose analog computers, which used a direct mechanical or electrical model of the problem as a basis for computation (they became increasingly rare after the development of the programmable digital computer). A succession of steadily more powerful and flexible computing devices were constructed in the 1930s and 1940s, gradually adding the key features of modern computers.

The use of digital electronics was introduced by Claude Shannon in 1937Shannon, Claude Elwood (1940). He came up with the idea while studying the relay circuits of Vannevar Bush's Differential Analyzer.{scienceworld.wolfram.com/biography/Shannon.html Biography of Claude Elwood Shannon] - URL retrieved September 26, 2006 This point marked the beginning of binary digital circuit design and the use of logic gates. Precursors of this idea were Almon Strowger, who patented a device containing a logic gate switch circuit, Nikola Tesla who filed for patents of devices containing logic gate circuits in 1898 (see List of Tesla patents), and Lee De Forest's modification, in 1907, who replaced relays with vacuum tubes.

Defining one point along this road as "the first digital electronic computer" is exceedingly difficult.
On 12 May, 1941 Konrad Zuse completed his electromechanical Z3, being the first working machine featuring automatic binary arithmetic and feasible programmability (therefore the first digital operational programmable computer, although not electronic); other notable achievements include the Atanasoff-Berry Computer (shown working around Summer 1941), a special-purpose machine that used valve-driven (vacuum tube) computation, binary numbers, and regenerative memory; the Harvard Mark I, a large-scale electromechanical computer with limited programmability (shown working around 1944); which was the first general purpose electronic computer, but originally had an inflexible architecture that meant reprogramming it essentially required it to be rewired.

The team who developed ENIAC, recognizing its flaws, came up with a far more flexible and elegant design, which has become known as the Von Neumann architecture (or "stored program architecture"). The first to be up and running was the Small-Scale Experimental Machine, but the EDSAC was perhaps the first practical version that was developed.

Valve (tube) driven computer designs were in use throughout the 1950s, but were eventually replaced with transistor-based computers, which were smaller, faster, cheaper, and much more reliable, thus allowing them to be commercially produced, in the 1960s. By the 1970s, the adoption of integrated circuit technology had enabled computers to be produced at a low enough cost to allow individuals to own personal computers.

How computers work: the stored program architecture

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While the technologies used in computers have changed dramatically since the first electronic, general-purpose computers of the 1940s, most still use the stored program architecture (sometimes called the von Neumann architecture). rewrite -->
The architecture describes a computer with four main sections: the arithmetic and logic unit (ALU), the control circuitry, the memory, and the input and output devices (collectively termed I/O). These parts are interconnected by bundles of wires (called "buses" when the same bundle supports more than one data path) and are usually driven by a timer or clock (although other events could drive the control circuitry).

Conceptually, a computer's memory can be viewed as a list of cells. This information can either be an instruction, telling the computer what to do, or data, the information which the computer is to process using the instructions that have been placed in the memory. In principle, any cell can be used to store either instructions or data.

The ALU is in many senses the heart of the computer. On a typical personal computer, input devices include objects like the keyboard and mouse, and output devices include computer monitors, printers and the like, but as will be discussed later a huge variety of devices can be connected to a computer and serve as I/O devices.

The control system ties this all together. typically, this is incremented each time an instruction is executed, unless the instruction itself indicates that the next instruction should be at some other location (allowing the computer to repeatedly execute the same instructions).

Since the 1980s the ALU and control unit (collectively called a central processing unit or CPU) have typically been located on a single integrated circuit called a microprocessor.

The functioning of such a computer is in principle quite straightforward.

Instructions, like data, are represented within the computer as binary code ? The particular instruction set that a specific computer supports is known as that computer's machine language.

More powerful computers such as minicomputers, mainframe computers and servers may differ from the model above by dividing their work between more than one main CPU. Multiprocessor and multicore personal and laptop computers are also beginning to become available.

Supercomputers often have highly unusual architectures significantly different from the basic stored-program architecture, sometimes featuring thousands of CPUs, but such designs tend to be useful only for specialized tasks. At the other end of the size scale, some microcontrollers use the Harvard architecture that ensures that program and data memory are logically separate.

Digital circuits

The conceptual design above could be implemented using a variety of different technologies. As previously mentioned, a stored program computer could be designed entirely of mechanical components like Babbage's devices or the Digi-Comp I. However, digital circuits allow Boolean logic and arithmetic using binary numerals to be implemented using relays ? when electricity is provided to one of the pins, current can flow through between the other two.

Through arrangements of logic gates, one can build digital circuits to do more complex tasks, for instance, an adder, which implements in electronics the same method ? in computer terminology, an algorithm ? Therefore, by the 1960s they were replaced by the transistor, a new device which performed the same task as the tube but was much smaller, faster operating, reliable, used much less power, and was far cheaper.

In the 1960s and 1970s, the transistor itself was gradually replaced by the integrated circuit, which placed multiple transistors (and other components) and the wires connecting them on a single, solid piece of silicon. By the 1970s, the entire ALU and control unit, the combination becoming known as a CPU, were being placed on a single "chip" called a microprocessor. as of 2006, the Intel Core Duo processor contains 151 million transistors.

Tubes, transistors, and transistors on integrated circuits can be used as the "storage" component of the stored-program architecture, using a circuit design known as a flip-flop, and indeed flip-flops are used for small amounts of very high-speed storage. Instead, earliest computers stored data in Williams tubes ? These results can either be viewed directly by a user, or they can be sent to another machine, whose control has been assigned to the computer: In a robot, for instance, the controlling computer's major output device is the robot itself.

The first generation of computers were equipped with a fairly limited range of input devices. A punch card reader, or something similar, was used to enter instructions and data into the computer's memory, and some kind of printer, usually a modified teletype, was used to record the results. For the personal computer, for instance, keyboards and mice are the primary ways people directly enter information into the computer; and monitors are the primary way in which information from the computer is presented back to the user, though printers, speakers, and headphones are common, too. The first class is that of secondary storage devices, such as hard disks, CD-ROMs, key drives and the like, which represent comparatively slow, but high-capacity devices, where information can be stored for later retrieval;

Programs

Computer programs are simply lists of instructions for the computer to execute. Rather, they do millions of simple instructions arranged by people known as programmers.

In practice, people do not normally write the instructions for computers directly in machine language. Instead, programmers describe the desired actions in a "high level" programming language which is then translated into the machine language automatically by special computer programs (interpreters and compilers). The language chosen for a particular task depends on the nature of the task, the skill set of the programmers, tool availability and, often, the requirements of the customers (for instance, projects for the US military were often required to be in the Ada programming language).

Computer software is an alternative term for computer programs; A computer application is a piece of computer software provided to many computer users, often in a retail environment. The stereotypical modern example of an application is perhaps the office suite, a set of interrelated programs for performing common office tasks.

Going from the extremely simple capabilities of a single machine language instruction to the myriad capabilities of application programs means that many computer programs are extremely large and complex. A typical example is Windows XP, created from roughly 40 million lines of computer code in the C++ programming language;Tanenbaum, Andrew S. the discipline of software engineering has attempted, with some success, to make the process quicker and more productive and improve the quality of the end product.

A problem or a model is computational if it is formalized in such way that can be transformed to the form of a computer program. the classic example of this type of early operating system was OS/360 by IBM.

The next major development in operating systems was timesharing ? Security access controls, allowing computer users access only to files, directories and programs they had permissions to use, were also common.

Perhaps the last major addition to the operating system was tools to provide programs with a standardized graphical user interface. For instance, Apple's Mac OS X ships with a digital video editor application.

Operating systems for smaller computers may not provide all of these functions. The operating systems for early microcomputers with limited memory and processing capability did not, and Embedded computers typically have specialized operating systems or no operating system at all, with their custom application programs performing the tasks that might otherwise be delegated to an operating system. The ENIAC was originally designed to calculate ballistics-firing tables for artillery, but it was also used to calculate neutron cross-sectional densities to help in the design of the hydrogen bomb significantly speeding up its development. (Many of the most powerful supercomputers available today are also used for nuclear weapons simulations.) The CSIR Mk I, the first Australian stored-program computer, was amongst many other tasks used for the evaluation of rainfall patterns for the catchment area of the Snowy Mountains Scheme, a large hydroelectric generation projectThe last of the first : CSIRAC : Australia's first computer, Doug McCann and Peter Thorne, ISBN 0-7340-2024-4. Others were used in cryptanalysis, for example the first programmable (though not general-purpose) digital electronic computer, Colossus, built in 1943 during World War II. The LEO, a stored program-computer built by in the United Kingdom, was operational and being used for inventory management and other purposes 3 years before IBM built their first commercial stored-program computer. In the 1980s, personal computers became popular for many tasks, including book-keeping, writing and printing documents, calculating forecasts and other repetitive mathematical tasks involving spreadsheets.

As computers have become less expensive, they have been used extensively in the creative arts as well. Sound, still pictures, and video are now routinely created (through synthesizers, computer graphics and computer animation), and near-universally edited by computer. They have also been used for entertainment, with the video game becoming a huge industry.

Computers have been used to control mechanical devices since they became small and cheap enough to do so; indeed, a major spur for integrated circuit technology was building a computer small enough to guide the Apollo missions two of the first major applications for embedded computers. Industrial robots have become commonplace in mass production, but general-purpose human-like robots have not lived up to the promise of their fictional counterparts and remain either toys or research projects.

Robotics, indeed, is the physical expression of the field of artificial intelligence, a discipline whose exact boundaries are fuzzy but to some degree involves attempting to give computers capabilities that they do not currently possess but humans do.

Networking and the Internet

Computers have been used to coordinate information in multiple locations since the 1950s, with the US military's SAGE system the first large-scale example of such a system, which led to a number of special-purpose commercial systems like Sabre.

In the 1970s, computer engineers at research institutions throughout the US began to link their computers together using telecommunications technology. This effort was funded by ARPA, and the computer network that it produced was called the ARPANET. In the phrase of John Gage and Bill Joy (of Sun Microsystems), "the network is the computer". Initially these facilities were available primarily to people working in high-tech environments, but in the 1990s the spread of applications like e-mail and the World Wide Web, combined with the development of cheap, fast networking technologies like Ethernet and ADSL saw computer networking become ubiquitous almost everywhere. A very large proportion of personal computers regularly connect to the Internet to communicate and receive information. "Wireless" networking, often utilizing mobile phone networks, has meant networking is becoming increasingly ubiquitous even in mobile computing environments. Therefore, there has been research interest in some computer models that use biological processes, or the oddities of quantum physics, to tackle these types of problems. However, such a system is limited by the maximum practical mass of DNA that can be handled.

Quantum computers, as the name implies, take advantage of the unusual world of quantum physics.

These alternative models for computation remain research projects at the present time, and will likely find application only for those problems where conventional computers are inadequate.

See also Unconventional computing. Terminology for different professional disciplines is still somewhat fluid and new fields emerge from time to time: however, some of the major groupings are as follows:

• Computer engineering is the branch of electrical engineering that focuses both on hardware and software design, and the interaction between the two.
  
• Computer science is a traditional name of the academic study of the processes related to computers and computation, such as developing efficient algorithms to perform specific class of tasks. one of many examples is experts in geographical information systems who apply computer technology to problems of managing geographical information.
  

There are three major professional societies dedicated to computers, the British Computer Society the Association for Computing Machinery and IEEE Computer Society.

See also

• Association for Computing Machinery
  
• The British Computer Society
  
• IEEE Computer Society
  
• Operating system
  
• Computer hardware
  
• Computability theory
  
• Computer datasheet
  
• Computer expo
  
• Computer science
  
• Computer types: analog computer, hybrid computer, supercomputer (along with the minisupercomputer), mainframe computer, workstation computers, laptop, roll-away computer, embedded computer, cart computer, tablet pc, handheld computer, subnotebook, thin client, minicomputer (and the supermini), microcomputer, computer terminal, and server
  
• Computing
  
• Computers in fiction
  
• Computer music
  
• Computer security and Computer insecurity challenges such as: malware, phishing, spam (electronic), and how to solve them, such as firewall, computer security audit
  
• Digital
  
• History of computing
  
• List of computer term etymologies
  
• List of computing topics
  
• Personal computer
  
• Word processing
  
• Internet
  
• Computer programming
  

Other computers

• Analog computer
  
• Chemical computer
  
• DNA computer
  
• Human computer
  
• Molecular computer
  
• Optical computer
  
• Quantum computer
  
• Wetware computer
  

See also Unconventional computing.

Notes and references