Any automatic device for the processing of information received in a prescribed and acceptable form according to a set of instructions. The instructions and information are stored in memory. The most widely used and most versatile of these devices is the digital computer, which can manipulate large amounts of information at high speed. Its input must be discrete rather than continuous and may consist of combinations of numbers, characters, and special symbols. Instructions – the program – are written in an appropriate programming language. The information is represented internally in binary form.
The development of microelectronics has allowed the corresponding development of a wide range of computers varying in size and complexity according to the required applications. Modern computers range from the microcomputer that contains typically a few billion logic circuits and a few billion words of memory to very large mainframe computers typically containing trillions of logic circuits and words of memory. The most powerful such devices are capable of performing over ten thousand trillion operations per second and can serve many users at the same time. Constant improvements in packing densities and subsequent miniaturization of circuits, coupled with improvements in speed of operation of the logic circuits is resulting in ever more powerful microcomputers and dramatic reductions in the physical size of mainframe computers.
Most computer systems consist of three basic elements: the central processing unit (CPU), the main memory, and peripheral devices involved with input/output and permanent storage of information. The CPU controls the operation of the system and performs arithmetic and logic operations on the data. The main memory stores the program and the data in units of bytes or words, each of which has a unique address, so that they may be retrieved quickly by the CPU. A cache memory is employed by high-performance systems: it interacts directly with the CPU and transfers information at extremely high speed. The information currently in active use is held in the cache. A complete computer system consists of the hardware – the electronic and other devices – and complementary software – the set of programs and data. A recent development that affects all computers from the smartphone upwards is that the CPU typically contains multiple processor cores, with internal memory, data buses, and caching.
The analogue computer is a device that accepts data as a continuously varying quantity rather than as a set of discrete items required by the digital computer. It is used in scientific experiments, simulation processes, and in the control of industrial processes where a constantly varying quantity can be monitored. A problem is solved by physical analogy, usually electrical. The magnitudes of the variables in an equation are represented by voltages fed to circuit elements connected in such a way that the input voltages interact according to the same equation as the original variables. The output voltage is then proportional to the numerical solution of the problem. It can solve or analyse many types of differential equations.