Back in the day before we had microcomputers, PLC's and DCS controlling our generators we had other systems. Initially these were mechanical and hydraulic based later moving to transistor equipment. Here we have a picture of such an automation system used to control a gas turbine. As you can see the controller is made up of many cards each performing a analogue electronic function. These may be addition, subtraction, integration, differentiation and various logic tasks. The whole lot is then interfaced through relays to the process plant. These systems took significant skill and time to design, commission and maintain. Imagine working with this and not having anywhere to plug a laptop in! In these days we used oscilloscopes and multi meters with resistance boxes and power supplies. And yet this was an improvement on the previous flapper and nozzle air systems.