An analog computer is a type of computer that uses physical rather than digital variables to solve problems. They can be made up of entirely mechanical, electrical, or hydraulic components that represent the problem being solved using continuous variation aspects of physical phenomena. 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. Analog computers were used long before the invention of digital computers and were especially well-suited to simulating dynamic systems. They could conduct simulations in real-time or at greatly accelerated rates, allowing experimentation by repeated runs with altered variables. Some key features of analog computers include:

• Operational Amplifiers: These are devices whose output current is proportional to its input potential difference. By causing this output current to flow through appropriate components, further potential differences were obtained, and a wide variety of mathematical operations, including inversion, summation, differentiation, and integration, could be carried out on them.

• VLSI Analog Chips: In a 2005 paper, Glenn E. R. Cowan described a Very-Large-Scale-Integrated Analog Computer (VLSI), i.e. an analog computer on a chip, so to speak. This chip delivered whopping 21 gigaflops per watt for a certain class of differential equations, which is better than today’s most power-efficient system in the Green500-list.

• Programming: Programming analog computers differs completely from everything students learn about programming digital computers.

Analog computers have largely been superseded by digital computers in industrial and scientific applications such as control systems and airplanes. However, analog computing holds great promise for the future. Analog computers could offer higher computational power than today’s 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.