An analog computer is a type of computer that uses physical rather than digital variables to solve problems. It uses continuously varying physical phenomena such as electrical, mechanical, or hydraulic quantities to model the problem being solved. Analog computers store information in physical quantities in a continuous format and use measurements to perform computation. They are suitable for measuring data that cannot be translated into numbers or codes. Any physical process that models some computation can be interpreted as an analog computer.

Analog computers were used long before the invention of digital computers. They were especially well-suited to simulating dynamic systems and could conduct simulations in real-time or at greatly accelerated rates, allowing experimentation by repeated runs. In the early 1970s, analog computer manufacturers tried to tie together their analog computer with a digital computer to get the advantages of the two techniques. In such systems, the digital computer controlled the analog computer, providing initial set-up, initiating multiple analog runs, and automatically feeding and collecting data.

Analog computing has largely been superseded by digital computing in industrial and scientific applications such as control systems and airplanes due to the wide range of complexities involved. However, analog computing holds great promise for the future, as it could offer higher computational power than todays supercomputers at comparable energy consumption or could be used in areas where only tiny amounts of energy are available, like implanted controllers in medicine and other embedded systems.