The term is used in distinction to digital computers, in which physical or mechanical phenomena are used to construct a finite-state machine which is then used to model the problem being solved. There is an intermediate group, Hybrid computers, in which a digital computer is used to control and organize inputs and outputs to and from attached analogue devices; for instance analogue devices might be used to help generate initial values for iterations.
Some examples:
Electronic analog computers are generally limited by noise and bandwidth considerations, and have been replaced by digital computers for almost all calculations. It may be stretching a point to regard physical simulations such as wind tunnels as analog computers.
A simple form of analog computation still in regular use is the nomogram.
These are examples of analog computers that have been constructed or practically used:
Computer theorists often refer to idealised analog computers as real computers (so called because they operate on the set of real numbers).
These idealised computers can in theory enable solve problems that are inextricable on digital computers.
Real analog computers are far from attaining this ideal, with noise and other errors completely swamping any hypothetical computation-theoretic advantages.
Also see signals, set theory, computability theory, differential equation, dynamical systems, chaos theory.
Practical analog computers
Analog synthesizers can also be viewed as a form of analog computer, and their technology was originally based on electronic analog computer technology.Idealised analog computers