# SPOTLIGHT ON SIZE

We’re used to the idea of digital computers varying in size from a laptop to a supercomputer, and analogue computers also varied in size. Desktop machines were aimed at the educational market, while ones occupying several large racks were used for more demanding applications. However, while the size of a digital computer has some a bearing on its speed of operation, things are quite different in the analogue domain.

Analogue computers aren’t universal computers but, even within their niche of simulation, no one machine is capable of solving any possible set of differential equations. For a start, the simplest of machines, like our emulator, didn’t have multipliers, and this limited what they could do. Other functional units that might not be available on small analogue computers include diode function generators and even some simple logic elements. However, there’s a more fundamental issue. Any analogue computer is limited by its number of functional units and the characteristics of those units – for example, how many inputs a summer or integrator has. So, the four integrators in our emulator allow it to solve, at most, four first-order differential equations, two second-order differential equations, two first-order and a secondorder differential equation, and so on. But this isn’t guaranteed as it also depends on how many potentiometers and summers are required. A large analogue computer – containing more functional units – could solve more complicated problems, but it wouldn’t be any faster.