A computer is a general purpose device that can be programmed to carry out a set of arithmetic or logical operations automatically. Since a sequence of operations can be readily changed, the computer can solve more than one kind of problem.
Conventionally, a computer consists of at least one processing element, typically a central processing unit (CPU), and some form of memory. The processing element carries out arithmetic and logic operations, and a sequencing and control unit can change the order of operations in response to stored information. Peripheral devices allow information to be retrieved from an external source, and the result of operations saved and retrieved.
Mechanical analog computers started appearing in the first century and were later used in the medieval era for astronomical calculations. In World War II, mechanical analog computers were used for specialized military applications such as calculating torpedo aiming. During this time the first electronic digital computers were developed. Originally they were the size of a large room, consuming as much power as several hundred modern personal computers (PCs).
Modern computers based on integrated circuits are millions to billions of times more capable than the early machines, and occupy a fraction of the space. Computers are small enough to fit into mobile devices, and mobile computers can be powered by small batteries. Personal computers in their various forms are icons of the Information Age and are generally considered as “computers”. However, the embedded computers found in many devices from MP3 players to fighter aircraft and from electronic toys to industrial robots are the most numerous.
Modern Computers Defined
Modern computers are electronic and digital. The actual machinery — wires, transistors, and circuits — is called hardware; the instructions and data are called software.
All general-purpose computers require the following hardware components:
Memory: enables a computer to store, at least temporarily, data and programs.
Mass storage device: allows a computer to permanently retain large amounts of data. Common mass storage devices include disk drives and tape drives.
Input device: usually a keyboard and mouse, the input device is the conduit through which data and instructions enter a computer.
Output device: a display screen, printer, or other device that lets you see what the computer has accomplished.
Central processing unit (CPU): the heart of the computer, this is the component that actually executes instructions.
In addition to these components, many others make it possible for the basic components to work together efficiently. For example, every computer requires a bus that transmits data from one part of the computer to another.
Computer Classification: By Size and Power
Computers can be generally classified by size and power as follows, though there is considerable overlap:
Personal computer: a small, single-user computer based on a microprocessor. In addition to the microprocessor, a personal computer has a keyboard for entering data, a monitor for displaying information, and a storage device for saving data.
Workstation: a powerful, single-user computer. A workstation is like a personal computer, but it has a more powerful microprocessor and a higher-quality monitor.
Minicomputer: a multi-user computer capable of supporting from 10 to hundreds of users simultaneously.
Mainframe: a powerful multi-user computer capable of supporting many hundreds or thousands of users simultaneously.
Supercomputer: an extremely fast computer that can perform hundreds of millions of instructions per second.
The First Digital Computer (USA)
The first digital computer in the United States, the ENIAC machine (John W. Mauchly and J. Presper Eckert at the University of Pennsylvania) used 18,000 vacuum tubes and trequired 167 square meters (1800 square feet) of floor space.