HYBRID COMPUTERS

We’ve painted a picture of analogue and digital computers as being totally unconnected, but this wasn’t always the case. An analogue computer can be connected to a digital computer, and the combination is referred to as a hybrid computer. These first appeared in the early ’60s and continued to be used until pure digital computers became fast enough to displace analogue computing.

The analogue computer part generally carried out the simulation by solving differential equations, while the digital computer provided overall control. This was possible by permitting the digital computer to read the outputs of the summers and integrators using analogueto-digital converters, to adjust potentiometer values, and to switch the operational mode of the analogue computer – for example, between Run, Hold (not included in our emulator, this mode stopped integrators integrating, thus halting the computation) and IC. A classic example is an optimisation problem. Let’s say we have a mathematical model of the trajectory of a projectile, and we want to adjust the angle of launch until we achieve a particular range. This is a trial and error process, but doing it manually on a pure analogue computer could be a laborious and timeconsuming sequence of setting the angle, running the simulation, observing the result, resetting the angle, running another simulation, and so on. All this changes with a hybrid computer. Although it would do the same sort of thing, it would do some more quickly by eliminating the need for human intervention.