Computers

A computer is a device capable of processing data according to a program — a list of instructions. The data to be processed may represent many types of information including numbers, text, pictures, or sound. more...

Computers can be extremely versatile. In fact, they are universal information processing machines. 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, from those of a personal digital assistant to a supercomputer. Therefore, the same computer designs have been adapted for tasks from processing company payrolls to controlling industrial robots. Modern electronic computers also have enormous speed and capacity for information processing compared to earlier designs, and they have become exponentially more powerful over the years (a phenomenon known as Moore's Law).

Computers are available in many physical forms. The original computers were the size of a large room, and such enormous computing facilities still exist for specialized scientific computation - supercomputers - and for the transaction processing requirements of large companies, generally called mainframes. Smaller computers for individual use, called personal computers, and their portable equivalent, the notebook computer, are ubiquitous information-processing and communication tools and are perhaps what most non-experts think of as "a computer". However, the most common form of computer in use today is the embedded computer, small computers used to control another device. Embedded computers control machines from fighter planes to digital cameras.

History of computing

Originally, a "computer" was a person who performed numerical calculations under the direction of a mathematician, often with the aid of a variety of mechanical calculating devices from the abacus onward. An example of an early computing device was the Antikythera mechanism, an ancient Greek device for calculating the movements of planets, dating from about 87 BCE. The technology responsible for this mysterious device seems to have been lost at some point.

The end of the Middle Ages saw a reinvigoration of European mathematics and engineering, and by the early 17th century a succession of mechanical calculating devices had been constructed using clockwork technology. A considerable number of technologies that would later prove vital for the digital computer were developed in the late 19th and early 20th centuries, such as the punched card and the vacuum tube ((or valve). Charles Babbage was the first to conceptualize and design a fully programmable computer as early as 1837, 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 (a trait that would in time doom thousands of computer-related engineering projects), the device was never actually constructed in his lifetime.

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 physical or electrical model of the problem as a basis for computation. These became increasingly rare after the development of the 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, such as the use of digital electronics (invented by Claude Shannon in 1937) and more flexible programmability. Defining one point along this road as "the first computer" is exceedingly difficult. Notable achievements include the Atanasoff Berry Computer, a special-purpose machine that used valve-driven computation and binary numbers; Konrad Zuse's Z machines; the secret British Colossus computer, which had limited programmability but demonstrated that a device using thousands of valves could be made reliable and reprogrammed electronically; and the American ENIAC — the first general purpose machine, but with 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 stored program architecture, which is the basis from which virtually all modern computers were derived. A number of projects to develop computers based on the stored program architecture commenced in the late 1940s; the first of these to be up and running was the Small-Scale Experimental Machine, but the EDSAC was perhaps the first practical version.

Valve-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 a personal computer of the type familiar today.

How computers work: the stored program architecture

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; as the article describes the primary inventors were probably ENIAC designers J. Presper Eckert and John William Mauchly). The design made the universal computer a practical reality.

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 a bundle of wires (a "bus") 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. Each cell has a numbered "address" and can store a small, fixed amount of information. 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.

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